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fuchsia / third_party / rust / 6e1d94708a0a4a35ca7e46c6cac98adf62fe800e / . / compiler / rustc_borrowck / src / diagnostics / conflict_errors.rs
blob: 6f0bd0543293cff02d76abb1760e8ee576c19602 [file] [log] [blame]
// ignore-tidy-filelength
#![allow(rustc::diagnostic_outside_of_impl)]
#![allow(rustc::untranslatable_diagnostic)]
use either::Either;
use hir::ClosureKind;
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{walk_block, walk_expr, Map, Visitor};
use rustc_hir::{CoroutineDesugaring, PatField};
use rustc_hir::{CoroutineKind, CoroutineSource, LangItem};
use rustc_middle::bug;
use rustc_middle::hir::nested_filter::OnlyBodies;
use rustc_middle::mir::tcx::PlaceTy;
use rustc_middle::mir::{
self, AggregateKind, BindingForm, BorrowKind, CallSource, ClearCrossCrate, ConstraintCategory,
FakeBorrowKind, FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, MutBorrowKind,
Operand, Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator,
TerminatorKind, VarBindingForm,
};
use rustc_middle::ty::{
self, suggest_constraining_type_params, PredicateKind, ToPredicate, Ty, TyCtxt,
TypeSuperVisitable, TypeVisitor,
};
use rustc_middle::util::CallKind;
use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
use rustc_span::def_id::DefId;
use rustc_span::def_id::LocalDefId;
use rustc_span::hygiene::DesugaringKind;
use rustc_span::symbol::{kw, sym, Ident};
use rustc_span::{BytePos, Span, Symbol};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;
use rustc_trait_selection::traits::error_reporting::FindExprBySpan;
use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
use std::iter;
use crate::borrow_set::TwoPhaseActivation;
use crate::borrowck_errors;
use crate::diagnostics::conflict_errors::StorageDeadOrDrop::LocalStorageDead;
use crate::diagnostics::{find_all_local_uses, CapturedMessageOpt};
use crate::{
borrow_set::BorrowData, diagnostics::Instance, prefixes::IsPrefixOf,
InitializationRequiringAction, MirBorrowckCtxt, WriteKind,
};
use super::{
explain_borrow::{BorrowExplanation, LaterUseKind},
DescribePlaceOpt, RegionName, RegionNameSource, UseSpans,
};
#[derive(Debug)]
struct MoveSite {
/// Index of the "move out" that we found. The `MoveData` can
/// then tell us where the move occurred.
moi: MoveOutIndex,
/// `true` if we traversed a back edge while walking from the point
/// of error to the move site.
traversed_back_edge: bool,
}
/// Which case a StorageDeadOrDrop is for.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum StorageDeadOrDrop<'tcx> {
LocalStorageDead,
BoxedStorageDead,
Destructor(Ty<'tcx>),
}
impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
pub(crate) fn report_use_of_moved_or_uninitialized(
&mut self,
location: Location,
desired_action: InitializationRequiringAction,
(moved_place, used_place, span): (PlaceRef<'tcx>, PlaceRef<'tcx>, Span),
mpi: MovePathIndex,
) {
debug!(
"report_use_of_moved_or_uninitialized: location={:?} desired_action={:?} \
moved_place={:?} used_place={:?} span={:?} mpi={:?}",
location, desired_action, moved_place, used_place, span, mpi
);
let use_spans =
self.move_spans(moved_place, location).or_else(|| self.borrow_spans(span, location));
let span = use_spans.args_or_use();
let (move_site_vec, maybe_reinitialized_locations) = self.get_moved_indexes(location, mpi);
debug!(
"report_use_of_moved_or_uninitialized: move_site_vec={:?} use_spans={:?}",
move_site_vec, use_spans
);
let move_out_indices: Vec<_> =
move_site_vec.iter().map(|move_site| move_site.moi).collect();
if move_out_indices.is_empty() {
let root_place = PlaceRef { projection: &[], ..used_place };
if !self.uninitialized_error_reported.insert(root_place) {
debug!(
"report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
root_place
);
return;
}
let err = self.report_use_of_uninitialized(
mpi,
used_place,
moved_place,
desired_action,
span,
use_spans,
);
self.buffer_error(err);
} else {
if let Some((reported_place, _)) = self.has_move_error(&move_out_indices) {
if used_place.is_prefix_of(*reported_place) {
debug!(
"report_use_of_moved_or_uninitialized place: error suppressed mois={:?}",
move_out_indices
);
return;
}
}
let is_partial_move = move_site_vec.iter().any(|move_site| {
let move_out = self.move_data.moves[(*move_site).moi];
let moved_place = &self.move_data.move_paths[move_out.path].place;
// `*(_1)` where `_1` is a `Box` is actually a move out.
let is_box_move = moved_place.as_ref().projection == [ProjectionElem::Deref]
&& self.body.local_decls[moved_place.local].ty.is_box();
!is_box_move
&& used_place != moved_place.as_ref()
&& used_place.is_prefix_of(moved_place.as_ref())
});
let partial_str = if is_partial_move { "partial " } else { "" };
let partially_str = if is_partial_move { "partially " } else { "" };
let mut err = self.cannot_act_on_moved_value(
span,
desired_action.as_noun(),
partially_str,
self.describe_place_with_options(
moved_place,
DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
),
);
let reinit_spans = maybe_reinitialized_locations
.iter()
.take(3)
.map(|loc| {
self.move_spans(self.move_data.move_paths[mpi].place.as_ref(), *loc)
.args_or_use()
})
.collect::<Vec<Span>>();
let reinits = maybe_reinitialized_locations.len();
if reinits == 1 {
err.span_label(reinit_spans[0], "this reinitialization might get skipped");
} else if reinits > 1 {
err.span_note(
MultiSpan::from_spans(reinit_spans),
if reinits <= 3 {
format!("these {reinits} reinitializations might get skipped")
} else {
format!(
"these 3 reinitializations and {} other{} might get skipped",
reinits - 3,
if reinits == 4 { "" } else { "s" }
)
},
);
}
let closure = self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
let mut is_loop_move = false;
let mut in_pattern = false;
let mut seen_spans = FxIndexSet::default();
for move_site in &move_site_vec {
let move_out = self.move_data.moves[(*move_site).moi];
let moved_place = &self.move_data.move_paths[move_out.path].place;
let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
let move_span = move_spans.args_or_use();
let is_move_msg = move_spans.for_closure();
let is_loop_message = location == move_out.source || move_site.traversed_back_edge;
if location == move_out.source {
is_loop_move = true;
}
if !seen_spans.contains(&move_span) {
if !closure {
self.suggest_ref_or_clone(mpi, &mut err, &mut in_pattern, move_spans);
}
let msg_opt = CapturedMessageOpt {
is_partial_move,
is_loop_message,
is_move_msg,
is_loop_move,
maybe_reinitialized_locations_is_empty: maybe_reinitialized_locations
.is_empty(),
};
self.explain_captures(
&mut err,
span,
move_span,
move_spans,
*moved_place,
msg_opt,
);
}
seen_spans.insert(move_span);
}
use_spans.var_path_only_subdiag(self.dcx(), &mut err, desired_action);
if !is_loop_move {
err.span_label(
span,
format!(
"value {} here after {partial_str}move",
desired_action.as_verb_in_past_tense(),
),
);
}
let ty = used_place.ty(self.body, self.infcx.tcx).ty;
let needs_note = match ty.kind() {
ty::Closure(id, _) => {
self.infcx.tcx.closure_kind_origin(id.expect_local()).is_none()
}
_ => true,
};
let mpi = self.move_data.moves[move_out_indices[0]].path;
let place = &self.move_data.move_paths[mpi].place;
let ty = place.ty(self.body, self.infcx.tcx).ty;
// If we're in pattern, we do nothing in favor of the previous suggestion (#80913).
// Same for if we're in a loop, see #101119.
if is_loop_move & !in_pattern && !matches!(use_spans, UseSpans::ClosureUse { .. }) {
if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
// We have a `&mut` ref, we need to reborrow on each iteration (#62112).
err.span_suggestion_verbose(
span.shrink_to_lo(),
format!(
"consider creating a fresh reborrow of {} here",
self.describe_place(moved_place)
.map(|n| format!("`{n}`"))
.unwrap_or_else(|| "the mutable reference".to_string()),
),
"&mut *",
Applicability::MachineApplicable,
);
}
}
let opt_name = self.describe_place_with_options(
place.as_ref(),
DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
);
let note_msg = match opt_name {
Some(name) => format!("`{name}`"),
None => "value".to_owned(),
};
if self.suggest_borrow_fn_like(&mut err, ty, &move_site_vec, &note_msg)
|| if let UseSpans::FnSelfUse { kind, .. } = use_spans
&& let CallKind::FnCall { fn_trait_id, self_ty } = kind
&& let ty::Param(_) = self_ty.kind()
&& ty == self_ty
&& Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait()
{
// this is a type parameter `T: FnOnce()`, don't suggest `T: FnOnce() + Clone`.
true
} else {
false
}
{
// Suppress the next suggestion since we don't want to put more bounds onto
// something that already has `Fn`-like bounds (or is a closure), so we can't
// restrict anyways.
} else {
let copy_did = self.infcx.tcx.require_lang_item(LangItem::Copy, Some(span));
self.suggest_adding_bounds(&mut err, ty, copy_did, span);
}
if needs_note {
if let Some(local) = place.as_local() {
let span = self.body.local_decls[local].source_info.span;
err.subdiagnostic(
self.dcx(),
crate::session_diagnostics::TypeNoCopy::Label {
is_partial_move,
ty,
place: &note_msg,
span,
},
);
} else {
err.subdiagnostic(
self.dcx(),
crate::session_diagnostics::TypeNoCopy::Note {
is_partial_move,
ty,
place: &note_msg,
},
);
};
}
if let UseSpans::FnSelfUse {
kind: CallKind::DerefCoercion { deref_target, deref_target_ty, .. },
..
} = use_spans
{
err.note(format!(
"{} occurs due to deref coercion to `{deref_target_ty}`",
desired_action.as_noun(),
));
// Check first whether the source is accessible (issue #87060)
if self.infcx.tcx.sess.source_map().is_span_accessible(deref_target) {
err.span_note(deref_target, "deref defined here");
}
}
self.buffer_move_error(move_out_indices, (used_place, err));
}
}
fn suggest_ref_or_clone(
&self,
mpi: MovePathIndex,
err: &mut Diag<'tcx>,
in_pattern: &mut bool,
move_spans: UseSpans<'tcx>,
) {
let move_span = match move_spans {
UseSpans::ClosureUse { capture_kind_span, .. } => capture_kind_span,
_ => move_spans.args_or_use(),
};
struct ExpressionFinder<'hir> {
expr_span: Span,
expr: Option<&'hir hir::Expr<'hir>>,
pat: Option<&'hir hir::Pat<'hir>>,
parent_pat: Option<&'hir hir::Pat<'hir>>,
hir: rustc_middle::hir::map::Map<'hir>,
}
impl<'hir> Visitor<'hir> for ExpressionFinder<'hir> {
type NestedFilter = OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.hir
}
fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
if e.span == self.expr_span {
self.expr = Some(e);
}
hir::intravisit::walk_expr(self, e);
}
fn visit_pat(&mut self, p: &'hir hir::Pat<'hir>) {
if p.span == self.expr_span {
self.pat = Some(p);
}
if let hir::PatKind::Binding(hir::BindingMode::NONE, _, i, sub) = p.kind {
if i.span == self.expr_span || p.span == self.expr_span {
self.pat = Some(p);
}
// Check if we are in a situation of `ident @ ident` where we want to suggest
// `ref ident @ ref ident` or `ref ident @ Struct { ref ident }`.
if let Some(subpat) = sub
&& self.pat.is_none()
{
self.visit_pat(subpat);
if self.pat.is_some() {
self.parent_pat = Some(p);
}
return;
}
}
hir::intravisit::walk_pat(self, p);
}
}
let hir = self.infcx.tcx.hir();
if let Some(body_id) = hir.maybe_body_owned_by(self.mir_def_id()) {
let expr = hir.body(body_id).value;
let place = &self.move_data.move_paths[mpi].place;
let span = place.as_local().map(|local| self.body.local_decls[local].source_info.span);
let mut finder = ExpressionFinder {
expr_span: move_span,
expr: None,
pat: None,
parent_pat: None,
hir,
};
finder.visit_expr(expr);
if let Some(span) = span
&& let Some(expr) = finder.expr
{
for (_, expr) in hir.parent_iter(expr.hir_id) {
if let hir::Node::Expr(expr) = expr {
if expr.span.contains(span) {
// If the let binding occurs within the same loop, then that
// loop isn't relevant, like in the following, the outermost `loop`
// doesn't play into `x` being moved.
// ```
// loop {
// let x = String::new();
// loop {
// foo(x);
// }
// }
// ```
break;
}
if let hir::ExprKind::Loop(.., loop_span) = expr.kind {
err.span_label(loop_span, "inside of this loop");
}
}
}
let typeck = self.infcx.tcx.typeck(self.mir_def_id());
let parent = self.infcx.tcx.parent_hir_node(expr.hir_id);
let (def_id, args, offset) = if let hir::Node::Expr(parent_expr) = parent
&& let hir::ExprKind::MethodCall(_, _, args, _) = parent_expr.kind
&& let Some(def_id) = typeck.type_dependent_def_id(parent_expr.hir_id)
{
(def_id.as_local(), args, 1)
} else if let hir::Node::Expr(parent_expr) = parent
&& let hir::ExprKind::Call(call, args) = parent_expr.kind
&& let ty::FnDef(def_id, _) = typeck.node_type(call.hir_id).kind()
{
(def_id.as_local(), args, 0)
} else {
(None, &[][..], 0)
};
if let Some(def_id) = def_id
&& let node = self.infcx.tcx.hir_node_by_def_id(def_id)
&& let Some(fn_sig) = node.fn_sig()
&& let Some(ident) = node.ident()
&& let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
&& let Some(arg) = fn_sig.decl.inputs.get(pos + offset)
{
let mut span: MultiSpan = arg.span.into();
span.push_span_label(
arg.span,
"this parameter takes ownership of the value".to_string(),
);
let descr = match node.fn_kind() {
Some(hir::intravisit::FnKind::ItemFn(..)) | None => "function",
Some(hir::intravisit::FnKind::Method(..)) => "method",
Some(hir::intravisit::FnKind::Closure) => "closure",
};
span.push_span_label(ident.span, format!("in this {descr}"));
err.span_note(
span,
format!(
"consider changing this parameter type in {descr} `{ident}` to borrow \
instead if owning the value isn't necessary",
),
);
}
let place = &self.move_data.move_paths[mpi].place;
let ty = place.ty(self.body, self.infcx.tcx).ty;
if let hir::Node::Expr(parent_expr) = parent
&& let hir::ExprKind::Call(call_expr, _) = parent_expr.kind
&& let hir::ExprKind::Path(hir::QPath::LangItem(LangItem::IntoIterIntoIter, _)) =
call_expr.kind
{
// Do not suggest `.clone()` in a `for` loop, we already suggest borrowing.
} else if let UseSpans::FnSelfUse { kind: CallKind::Normal { .. }, .. } = move_spans
{
// We already suggest cloning for these cases in `explain_captures`.
} else if let UseSpans::ClosureUse {
closure_kind:
ClosureKind::Coroutine(CoroutineKind::Desugared(_, CoroutineSource::Block)),
..
} = move_spans
{
self.suggest_cloning(err, ty, expr, None, Some(move_spans));
} else if self.suggest_hoisting_call_outside_loop(err, expr) {
// The place where the type moves would be misleading to suggest clone.
// #121466
self.suggest_cloning(err, ty, expr, None, Some(move_spans));
}
}
if let Some(pat) = finder.pat {
*in_pattern = true;
let mut sugg = vec![(pat.span.shrink_to_lo(), "ref ".to_string())];
if let Some(pat) = finder.parent_pat {
sugg.insert(0, (pat.span.shrink_to_lo(), "ref ".to_string()));
}
err.multipart_suggestion_verbose(
"borrow this binding in the pattern to avoid moving the value",
sugg,
Applicability::MachineApplicable,
);
}
}
}
fn report_use_of_uninitialized(
&self,
mpi: MovePathIndex,
used_place: PlaceRef<'tcx>,
moved_place: PlaceRef<'tcx>,
desired_action: InitializationRequiringAction,
span: Span,
use_spans: UseSpans<'tcx>,
) -> Diag<'tcx> {
// We need all statements in the body where the binding was assigned to later find all
// the branching code paths where the binding *wasn't* assigned to.
let inits = &self.move_data.init_path_map[mpi];
let move_path = &self.move_data.move_paths[mpi];
let decl_span = self.body.local_decls[move_path.place.local].source_info.span;
let mut spans = vec![];
for init_idx in inits {
let init = &self.move_data.inits[*init_idx];
let span = init.span(self.body);
if !span.is_dummy() {
spans.push(span);
}
}
let (name, desc) = match self.describe_place_with_options(
moved_place,
DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
) {
Some(name) => (format!("`{name}`"), format!("`{name}` ")),
None => ("the variable".to_string(), String::new()),
};
let path = match self.describe_place_with_options(
used_place,
DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
) {
Some(name) => format!("`{name}`"),
None => "value".to_string(),
};
// We use the statements were the binding was initialized, and inspect the HIR to look
// for the branching codepaths that aren't covered, to point at them.
let map = self.infcx.tcx.hir();
let body_id = map.body_owned_by(self.mir_def_id());
let body = map.body(body_id);
let mut visitor = ConditionVisitor { spans: &spans, name: &name, errors: vec![] };
visitor.visit_body(body);
let mut show_assign_sugg = false;
let isnt_initialized = if let InitializationRequiringAction::PartialAssignment
| InitializationRequiringAction::Assignment = desired_action
{
// The same error is emitted for bindings that are *sometimes* initialized and the ones
// that are *partially* initialized by assigning to a field of an uninitialized
// binding. We differentiate between them for more accurate wording here.
"isn't fully initialized"
} else if !spans.iter().any(|i| {
// We filter these to avoid misleading wording in cases like the following,
// where `x` has an `init`, but it is in the same place we're looking at:
// ```
// let x;
// x += 1;
// ```
!i.contains(span)
// We filter these to avoid incorrect main message on `match-cfg-fake-edges.rs`
&& !visitor
.errors
.iter()
.map(|(sp, _)| *sp)
.any(|sp| span < sp && !sp.contains(span))
}) {
show_assign_sugg = true;
"isn't initialized"
} else {
"is possibly-uninitialized"
};
let used = desired_action.as_general_verb_in_past_tense();
let mut err = struct_span_code_err!(
self.dcx(),
span,
E0381,
"{used} binding {desc}{isnt_initialized}"
);
use_spans.var_path_only_subdiag(self.dcx(), &mut err, desired_action);
if let InitializationRequiringAction::PartialAssignment
| InitializationRequiringAction::Assignment = desired_action
{
err.help(
"partial initialization isn't supported, fully initialize the binding with a \
default value and mutate it, or use `std::mem::MaybeUninit`",
);
}
err.span_label(span, format!("{path} {used} here but it {isnt_initialized}"));
let mut shown = false;
for (sp, label) in visitor.errors {
if sp < span && !sp.overlaps(span) {
// When we have a case like `match-cfg-fake-edges.rs`, we don't want to mention
// match arms coming after the primary span because they aren't relevant:
// ```
// let x;
// match y {
// _ if { x = 2; true } => {}
// _ if {
// x; //~ ERROR
// false
// } => {}
// _ => {} // We don't want to point to this.
// };
// ```
err.span_label(sp, label);
shown = true;
}
}
if !shown {
for sp in &spans {
if *sp < span && !sp.overlaps(span) {
err.span_label(*sp, "binding initialized here in some conditions");
}
}
}
err.span_label(decl_span, "binding declared here but left uninitialized");
if show_assign_sugg {
struct LetVisitor {
decl_span: Span,
sugg_span: Option<Span>,
}
impl<'v> Visitor<'v> for LetVisitor {
fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
if self.sugg_span.is_some() {
return;
}
// FIXME: We make sure that this is a normal top-level binding,
// but we could suggest `todo!()` for all uninitialized bindings in the pattern pattern
if let hir::StmtKind::Let(hir::LetStmt { span, ty, init: None, pat, .. }) =
&ex.kind
&& let hir::PatKind::Binding(..) = pat.kind
&& span.contains(self.decl_span)
{
self.sugg_span = ty.map_or(Some(self.decl_span), |ty| Some(ty.span));
}
hir::intravisit::walk_stmt(self, ex);
}
}
let mut visitor = LetVisitor { decl_span, sugg_span: None };
visitor.visit_body(body);
if let Some(span) = visitor.sugg_span {
self.suggest_assign_value(&mut err, moved_place, span);
}
}
err
}
fn suggest_assign_value(
&self,
err: &mut Diag<'_>,
moved_place: PlaceRef<'tcx>,
sugg_span: Span,
) {
let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
debug!("ty: {:?}, kind: {:?}", ty, ty.kind());
let Some(assign_value) = self.infcx.err_ctxt().ty_kind_suggestion(self.param_env, ty)
else {
return;
};
err.span_suggestion_verbose(
sugg_span.shrink_to_hi(),
"consider assigning a value",
format!(" = {assign_value}"),
Applicability::MaybeIncorrect,
);
}
fn suggest_borrow_fn_like(
&self,
err: &mut Diag<'_>,
ty: Ty<'tcx>,
move_sites: &[MoveSite],
value_name: &str,
) -> bool {
let tcx = self.infcx.tcx;
// Find out if the predicates show that the type is a Fn or FnMut
let find_fn_kind_from_did = |(pred, _): (ty::Clause<'tcx>, _)| {
if let ty::ClauseKind::Trait(pred) = pred.kind().skip_binder()
&& pred.self_ty() == ty
{
if Some(pred.def_id()) == tcx.lang_items().fn_trait() {
return Some(hir::Mutability::Not);
} else if Some(pred.def_id()) == tcx.lang_items().fn_mut_trait() {
return Some(hir::Mutability::Mut);
}
}
None
};
// If the type is opaque/param/closure, and it is Fn or FnMut, let's suggest (mutably)
// borrowing the type, since `&mut F: FnMut` iff `F: FnMut` and similarly for `Fn`.
// These types seem reasonably opaque enough that they could be instantiated with their
// borrowed variants in a function body when we see a move error.
let borrow_level = match *ty.kind() {
ty::Param(_) => tcx
.explicit_predicates_of(self.mir_def_id().to_def_id())
.predicates
.iter()
.copied()
.find_map(find_fn_kind_from_did),
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => tcx
.explicit_item_super_predicates(def_id)
.iter_instantiated_copied(tcx, args)
.find_map(|(clause, span)| find_fn_kind_from_did((clause, span))),
ty::Closure(_, args) => match args.as_closure().kind() {
ty::ClosureKind::Fn => Some(hir::Mutability::Not),
ty::ClosureKind::FnMut => Some(hir::Mutability::Mut),
_ => None,
},
_ => None,
};
let Some(borrow_level) = borrow_level else {
return false;
};
let sugg = move_sites
.iter()
.map(|move_site| {
let move_out = self.move_data.moves[(*move_site).moi];
let moved_place = &self.move_data.move_paths[move_out.path].place;
let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
let move_span = move_spans.args_or_use();
let suggestion = borrow_level.ref_prefix_str().to_owned();
(move_span.shrink_to_lo(), suggestion)
})
.collect();
err.multipart_suggestion_verbose(
format!("consider {}borrowing {value_name}", borrow_level.mutably_str()),
sugg,
Applicability::MaybeIncorrect,
);
true
}
/// In a move error that occurs on a call within a loop, we try to identify cases where cloning
/// the value would lead to a logic error. We infer these cases by seeing if the moved value is
/// part of the logic to break the loop, either through an explicit `break` or if the expression
/// is part of a `while let`.
fn suggest_hoisting_call_outside_loop(&self, err: &mut Diag<'_>, expr: &hir::Expr<'_>) -> bool {
let tcx = self.infcx.tcx;
let mut can_suggest_clone = true;
// If the moved value is a locally declared binding, we'll look upwards on the expression
// tree until the scope where it is defined, and no further, as suggesting to move the
// expression beyond that point would be illogical.
let local_hir_id = if let hir::ExprKind::Path(hir::QPath::Resolved(
_,
hir::Path { res: hir::def::Res::Local(local_hir_id), .. },
)) = expr.kind
{
Some(local_hir_id)
} else {
// This case would be if the moved value comes from an argument binding, we'll just
// look within the entire item, that's fine.
None
};
/// This will allow us to look for a specific `HirId`, in our case `local_hir_id` where the
/// binding was declared, within any other expression. We'll use it to search for the
/// binding declaration within every scope we inspect.
struct Finder {
hir_id: hir::HirId,
found: bool,
}
impl<'hir> Visitor<'hir> for Finder {
fn visit_pat(&mut self, pat: &'hir hir::Pat<'hir>) {
if pat.hir_id == self.hir_id {
self.found = true;
}
hir::intravisit::walk_pat(self, pat);
}
fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
if ex.hir_id == self.hir_id {
self.found = true;
}
hir::intravisit::walk_expr(self, ex);
}
}
// The immediate HIR parent of the moved expression. We'll look for it to be a call.
let mut parent = None;
// The top-most loop where the moved expression could be moved to a new binding.
let mut outer_most_loop: Option<&hir::Expr<'_>> = None;
for (_, node) in tcx.hir().parent_iter(expr.hir_id) {
let e = match node {
hir::Node::Expr(e) => e,
hir::Node::LetStmt(hir::LetStmt { els: Some(els), .. }) => {
let mut finder = BreakFinder { found_breaks: vec![], found_continues: vec![] };
finder.visit_block(els);
if !finder.found_breaks.is_empty() {
// Don't suggest clone as it could be will likely end in an infinite
// loop.
// let Some(_) = foo(non_copy.clone()) else { break; }
// --- ^^^^^^^^ -----
can_suggest_clone = false;
}
continue;
}
_ => continue,
};
if let Some(&hir_id) = local_hir_id {
let mut finder = Finder { hir_id, found: false };
finder.visit_expr(e);
if finder.found {
// The current scope includes the declaration of the binding we're accessing, we
// can't look up any further for loops.
break;
}
}
if parent.is_none() {
parent = Some(e);
}
match e.kind {
hir::ExprKind::Let(_) => {
match tcx.parent_hir_node(e.hir_id) {
hir::Node::Expr(hir::Expr {
kind: hir::ExprKind::If(cond, ..), ..
}) => {
let mut finder = Finder { hir_id: expr.hir_id, found: false };
finder.visit_expr(cond);
if finder.found {
// The expression where the move error happened is in a `while let`
// condition Don't suggest clone as it will likely end in an
// infinite loop.
// while let Some(_) = foo(non_copy.clone()) { }
// --------- ^^^^^^^^
can_suggest_clone = false;
}
}
_ => {}
}
}
hir::ExprKind::Loop(..) => {
outer_most_loop = Some(e);
}
_ => {}
}
}
let loop_count: usize = tcx
.hir()
.parent_iter(expr.hir_id)
.map(|(_, node)| match node {
hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Loop(..), .. }) => 1,
_ => 0,
})
.sum();
let sm = tcx.sess.source_map();
if let Some(in_loop) = outer_most_loop {
let mut finder = BreakFinder { found_breaks: vec![], found_continues: vec![] };
finder.visit_expr(in_loop);
// All of the spans for `break` and `continue` expressions.
let spans = finder
.found_breaks
.iter()
.chain(finder.found_continues.iter())
.map(|(_, span)| *span)
.filter(|span| {
!matches!(
span.desugaring_kind(),
Some(DesugaringKind::ForLoop | DesugaringKind::WhileLoop)
)
})
.collect::<Vec<Span>>();
// All of the spans for the loops above the expression with the move error.
let loop_spans: Vec<_> = tcx
.hir()
.parent_iter(expr.hir_id)
.filter_map(|(_, node)| match node {
hir::Node::Expr(hir::Expr { span, kind: hir::ExprKind::Loop(..), .. }) => {
Some(*span)
}
_ => None,
})
.collect();
// It is possible that a user written `break` or `continue` is in the wrong place. We
// point them out at the user for them to make a determination. (#92531)
if !spans.is_empty() && loop_count > 1 {
// Getting fancy: if the spans of the loops *do not* overlap, we only use the line
// number when referring to them. If there *are* overlaps (multiple loops on the
// same line) then we use the more verbose span output (`file.rs:col:ll`).
let mut lines: Vec<_> =
loop_spans.iter().map(|sp| sm.lookup_char_pos(sp.lo()).line).collect();
lines.sort();
lines.dedup();
let fmt_span = |span: Span| {
if lines.len() == loop_spans.len() {
format!("line {}", sm.lookup_char_pos(span.lo()).line)
} else {
sm.span_to_diagnostic_string(span)
}
};
let mut spans: MultiSpan = spans.into();
// Point at all the `continue`s and explicit `break`s in the relevant loops.
for (desc, elements) in [
("`break` exits", &finder.found_breaks),
("`continue` advances", &finder.found_continues),
] {
for (destination, sp) in elements {
if let Ok(hir_id) = destination.target_id
&& let hir::Node::Expr(expr) = tcx.hir().hir_node(hir_id)
&& !matches!(
sp.desugaring_kind(),
Some(DesugaringKind::ForLoop | DesugaringKind::WhileLoop)
)
{
spans.push_span_label(
*sp,
format!("this {desc} the loop at {}", fmt_span(expr.span)),
);
}
}
}
// Point at all the loops that are between this move and the parent item.
for span in loop_spans {
spans.push_span_label(sm.guess_head_span(span), "");
}
// note: verify that your loop breaking logic is correct
// --> $DIR/nested-loop-moved-value-wrong-continue.rs:41:17
// |
// 28 | for foo in foos {
// | ---------------
// ...
// 33 | for bar in &bars {
// | ----------------
// ...
// 41 | continue;
// | ^^^^^^^^ this `continue` advances the loop at line 33
err.span_note(spans, "verify that your loop breaking logic is correct");
}
if let Some(parent) = parent
&& let hir::ExprKind::MethodCall(..) | hir::ExprKind::Call(..) = parent.kind
{
// FIXME: We could check that the call's *parent* takes `&mut val` to make the
// suggestion more targeted to the `mk_iter(val).next()` case. Maybe do that only to
// check for whether to suggest `let value` or `let mut value`.
let span = in_loop.span;
if !finder.found_breaks.is_empty()
&& let Ok(value) = sm.span_to_snippet(parent.span)
{
// We know with high certainty that this move would affect the early return of a
// loop, so we suggest moving the expression with the move out of the loop.
let indent = if let Some(indent) = sm.indentation_before(span) {
format!("\n{indent}")
} else {
" ".to_string()
};
err.multipart_suggestion(
"consider moving the expression out of the loop so it is only moved once",
vec![
(parent.span, "value".to_string()),
(span.shrink_to_lo(), format!("let mut value = {value};{indent}")),
],
Applicability::MaybeIncorrect,
);
}
}
}
can_suggest_clone
}
/// We have `S { foo: val, ..base }`, and we suggest instead writing
/// `S { foo: val, bar: base.bar.clone(), .. }` when valid.
fn suggest_cloning_on_functional_record_update(
&self,
err: &mut Diag<'_>,
ty: Ty<'tcx>,
expr: &'cx hir::Expr<'cx>,
) {
let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
let hir::ExprKind::Struct(struct_qpath, fields, Some(base)) = expr.kind else { return };
let hir::QPath::Resolved(_, path) = struct_qpath else { return };
let hir::def::Res::Def(_, def_id) = path.res else { return };
let Some(expr_ty) = typeck_results.node_type_opt(expr.hir_id) else { return };
let ty::Adt(def, args) = expr_ty.kind() else { return };
let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = base.kind else { return };
let (hir::def::Res::Local(_)
| hir::def::Res::Def(
DefKind::Const | DefKind::ConstParam | DefKind::Static { .. } | DefKind::AssocConst,
_,
)) = path.res
else {
return;
};
let Ok(base_str) = self.infcx.tcx.sess.source_map().span_to_snippet(base.span) else {
return;
};
// 1. look for the fields of type `ty`.
// 2. check if they are clone and add them to suggestion
// 3. check if there are any values left to `..` and remove it if not
// 4. emit suggestion to clone the field directly as `bar: base.bar.clone()`
let mut final_field_count = fields.len();
let Some(variant) = def.variants().iter().find(|variant| variant.def_id == def_id) else {
// When we have an enum, look for the variant that corresponds to the variant the user
// wrote.
return;
};
let mut sugg = vec![];
for field in &variant.fields {
// In practice unless there are more than one field with the same type, we'll be
// suggesting a single field at a type, because we don't aggregate multiple borrow
// checker errors involving the functional record update sytnax into a single one.
let field_ty = field.ty(self.infcx.tcx, args);
let ident = field.ident(self.infcx.tcx);
if field_ty == ty && fields.iter().all(|field| field.ident.name != ident.name) {
// Suggest adding field and cloning it.
sugg.push(format!("{ident}: {base_str}.{ident}.clone()"));
final_field_count += 1;
}
}
let (span, sugg) = match fields {
[.., last] => (
if final_field_count == variant.fields.len() {
// We'll remove the `..base` as there aren't any fields left.
last.span.shrink_to_hi().with_hi(base.span.hi())
} else {
last.span.shrink_to_hi()
},
format!(", {}", sugg.join(", ")),
),
// Account for no fields in suggestion span.
[] => (
expr.span.with_lo(struct_qpath.span().hi()),
if final_field_count == variant.fields.len() {
// We'll remove the `..base` as there aren't any fields left.
format!(" {{ {} }}", sugg.join(", "))
} else {
format!(" {{ {}, ..{base_str} }}", sugg.join(", "))
},
),
};
let prefix = if !self.implements_clone(ty) {
let msg = format!("`{ty}` doesn't implement `Copy` or `Clone`");
if let ty::Adt(def, _) = ty.kind() {
err.span_note(self.infcx.tcx.def_span(def.did()), msg);
} else {
err.note(msg);
}
format!("if `{ty}` implemented `Clone`, you could ")
} else {
String::new()
};
let msg = format!(
"{prefix}clone the value from the field instead of using the functional record update \
syntax",
);
err.span_suggestion_verbose(span, msg, sugg, Applicability::MachineApplicable);
}
pub(crate) fn suggest_cloning(
&self,
err: &mut Diag<'_>,
ty: Ty<'tcx>,
mut expr: &'cx hir::Expr<'cx>,
mut other_expr: Option<&'cx hir::Expr<'cx>>,
use_spans: Option<UseSpans<'tcx>>,
) {
if let hir::ExprKind::Struct(_, _, Some(_)) = expr.kind {
// We have `S { foo: val, ..base }`. In `check_aggregate_rvalue` we have a single
// `Location` that covers both the `S { ... }` literal, all of its fields and the
// `base`. If the move happens because of `S { foo: val, bar: base.bar }` the `expr`
// will already be correct. Instead, we see if we can suggest writing.
self.suggest_cloning_on_functional_record_update(err, ty, expr);
return;
}
if let Some(some_other_expr) = other_expr
&& let Some(parent_binop) =
self.infcx.tcx.hir().parent_iter(expr.hir_id).find_map(|n| {
if let (hir_id, hir::Node::Expr(e)) = n
&& let hir::ExprKind::AssignOp(_binop, target, _arg) = e.kind
&& target.hir_id == expr.hir_id
{
Some(hir_id)
} else {
None
}
})
&& let Some(other_parent_binop) =
self.infcx.tcx.hir().parent_iter(some_other_expr.hir_id).find_map(|n| {
if let (hir_id, hir::Node::Expr(expr)) = n
&& let hir::ExprKind::AssignOp(..) = expr.kind
{
Some(hir_id)
} else {
None
}
})
&& parent_binop == other_parent_binop
{
// Explicitly look for `expr += other_expr;` and avoid suggesting
// `expr.clone() += other_expr;`, instead suggesting `expr += other_expr.clone();`.
other_expr = Some(expr);
expr = some_other_expr;
}
'outer: {
if let ty::Ref(..) = ty.kind() {
// We check for either `let binding = foo(expr, other_expr);` or
// `foo(expr, other_expr);` and if so we don't suggest an incorrect
// `foo(expr, other_expr).clone()`
if let Some(other_expr) = other_expr
&& let Some(parent_let) =
self.infcx.tcx.hir().parent_iter(expr.hir_id).find_map(|n| {
if let (hir_id, hir::Node::LetStmt(_) | hir::Node::Stmt(_)) = n {
Some(hir_id)
} else {
None
}
})
&& let Some(other_parent_let) =
self.infcx.tcx.hir().parent_iter(other_expr.hir_id).find_map(|n| {
if let (hir_id, hir::Node::LetStmt(_) | hir::Node::Stmt(_)) = n {
Some(hir_id)
} else {
None
}
})
&& parent_let == other_parent_let
{
// Explicitly check that we don't have `foo(&*expr, other_expr)`, as cloning the
// result of `foo(...)` won't help.
break 'outer;
}
// We're suggesting `.clone()` on an borrowed value. See if the expression we have
// is an argument to a function or method call, and try to suggest cloning the
// *result* of the call, instead of the argument. This is closest to what people
// would actually be looking for in most cases, with maybe the exception of things
// like `fn(T) -> T`, but even then it is reasonable.
let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
let mut prev = expr;
while let hir::Node::Expr(parent) = self.infcx.tcx.parent_hir_node(prev.hir_id) {
if let hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) = parent.kind
&& let Some(call_ty) = typeck_results.node_type_opt(parent.hir_id)
&& let call_ty = call_ty.peel_refs()
&& (!call_ty
.walk()
.any(|t| matches!(t.unpack(), ty::GenericArgKind::Lifetime(_)))
|| if let ty::Alias(ty::Projection, _) = call_ty.kind() {
// FIXME: this isn't quite right with lifetimes on assoc types,
// but ignore for now. We will only suggest cloning if
// `<Ty as Trait>::Assoc: Clone`, which should keep false positives
// down to a managable ammount.
true
} else {
false
})
&& self.implements_clone(call_ty)
&& self.suggest_cloning_inner(err, call_ty, parent)
{
return;
}
prev = parent;
}
}
}
let ty = ty.peel_refs();
if self.implements_clone(ty) {
self.suggest_cloning_inner(err, ty, expr);
} else if let ty::Adt(def, args) = ty.kind()
&& def.did().as_local().is_some()
&& def.variants().iter().all(|variant| {
variant
.fields
.iter()
.all(|field| self.implements_clone(field.ty(self.infcx.tcx, args)))
})
{
let ty_span = self.infcx.tcx.def_span(def.did());
let mut span: MultiSpan = ty_span.into();
span.push_span_label(ty_span, "consider implementing `Clone` for this type");
span.push_span_label(expr.span, "you could clone this value");
err.span_note(
span,
format!("if `{ty}` implemented `Clone`, you could clone the value"),
);
} else if let ty::Param(param) = ty.kind()
&& let Some(_clone_trait_def) = self.infcx.tcx.lang_items().clone_trait()
&& let generics = self.infcx.tcx.generics_of(self.mir_def_id())
&& let generic_param = generics.type_param(*param, self.infcx.tcx)
&& let param_span = self.infcx.tcx.def_span(generic_param.def_id)
&& if let Some(UseSpans::FnSelfUse { kind, .. }) = use_spans
&& let CallKind::FnCall { fn_trait_id, self_ty } = kind
&& let ty::Param(_) = self_ty.kind()
&& ty == self_ty
&& [
self.infcx.tcx.lang_items().fn_once_trait(),
self.infcx.tcx.lang_items().fn_mut_trait(),
self.infcx.tcx.lang_items().fn_trait(),
]
.contains(&Some(fn_trait_id))
{
// Do not suggest `F: FnOnce() + Clone`.
false
} else {
true
}
{
let mut span: MultiSpan = param_span.into();
span.push_span_label(
param_span,
"consider constraining this type parameter with `Clone`",
);
span.push_span_label(expr.span, "you could clone this value");
err.span_help(
span,
format!("if `{ty}` implemented `Clone`, you could clone the value"),
);
}
}
pub(crate) fn implements_clone(&self, ty: Ty<'tcx>) -> bool {
let Some(clone_trait_def) = self.infcx.tcx.lang_items().clone_trait() else { return false };
self.infcx
.type_implements_trait(clone_trait_def, [ty], self.param_env)
.must_apply_modulo_regions()
}
/// Given an expression, check if it is a method call `foo.clone()`, where `foo` and
/// `foo.clone()` both have the same type, returning the span for `.clone()` if so.
pub(crate) fn clone_on_reference(&self, expr: &hir::Expr<'_>) -> Option<Span> {
let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
if let hir::ExprKind::MethodCall(segment, rcvr, args, span) = expr.kind
&& let Some(expr_ty) = typeck_results.node_type_opt(expr.hir_id)
&& let Some(rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id)
&& rcvr_ty == expr_ty
&& segment.ident.name == sym::clone
&& args.is_empty()
{
Some(span)
} else {
None
}
}
fn in_move_closure(&self, expr: &hir::Expr<'_>) -> bool {
for (_, node) in self.infcx.tcx.hir().parent_iter(expr.hir_id) {
if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(closure), .. }) = node
&& let hir::CaptureBy::Value { .. } = closure.capture_clause
{
// `move || x.clone()` will not work. FIXME: suggest `let y = x.clone(); move || y`
return true;
}
}
false
}
fn suggest_cloning_inner(
&self,
err: &mut Diag<'_>,
ty: Ty<'tcx>,
expr: &hir::Expr<'_>,
) -> bool {
let tcx = self.infcx.tcx;
if let Some(_) = self.clone_on_reference(expr) {
// Avoid redundant clone suggestion already suggested in `explain_captures`.
// See `tests/ui/moves/needs-clone-through-deref.rs`
return false;
}
if self.in_move_closure(expr) {
return false;
}
// Try to find predicates on *generic params* that would allow copying `ty`
let suggestion =
if let Some(symbol) = tcx.hir().maybe_get_struct_pattern_shorthand_field(expr) {
format!(": {symbol}.clone()")
} else {
".clone()".to_owned()
};
let mut sugg = Vec::with_capacity(2);
let mut inner_expr = expr;
// Remove uses of `&` and `*` when suggesting `.clone()`.
while let hir::ExprKind::AddrOf(.., inner) | hir::ExprKind::Unary(hir::UnOp::Deref, inner) =
&inner_expr.kind
{
if let hir::ExprKind::AddrOf(_, hir::Mutability::Mut, _) = inner_expr.kind {
// We assume that `&mut` refs are desired for their side-effects, so cloning the
// value wouldn't do what the user wanted.
return false;
}
inner_expr = inner;
}
if inner_expr.span.lo() != expr.span.lo() {
sugg.push((expr.span.with_hi(inner_expr.span.lo()), String::new()));
}
let span = if inner_expr.span.hi() != expr.span.hi() {
// Account for `(*x)` to suggest `x.clone()`.
expr.span.with_lo(inner_expr.span.hi())
} else {
expr.span.shrink_to_hi()
};
sugg.push((span, suggestion));
let msg = if let ty::Adt(def, _) = ty.kind()
&& [tcx.get_diagnostic_item(sym::Arc), tcx.get_diagnostic_item(sym::Rc)]
.contains(&Some(def.did()))
{
"clone the value to increment its reference count"
} else {
"consider cloning the value if the performance cost is acceptable"
};
err.multipart_suggestion_verbose(msg, sugg, Applicability::MachineApplicable);
true
}
fn suggest_adding_bounds(&self, err: &mut Diag<'_>, ty: Ty<'tcx>, def_id: DefId, span: Span) {
let tcx = self.infcx.tcx;
let generics = tcx.generics_of(self.mir_def_id());
let Some(hir_generics) = tcx
.typeck_root_def_id(self.mir_def_id().to_def_id())
.as_local()
.and_then(|def_id| tcx.hir().get_generics(def_id))
else {
return;
};
// Try to find predicates on *generic params* that would allow copying `ty`
let ocx = ObligationCtxt::new(self.infcx);
let cause = ObligationCause::misc(span, self.mir_def_id());
ocx.register_bound(cause, self.param_env, ty, def_id);
let errors = ocx.select_all_or_error();
// Only emit suggestion if all required predicates are on generic
let predicates: Result<Vec<_>, _> = errors
.into_iter()
.map(|err| match err.obligation.predicate.kind().skip_binder() {
PredicateKind::Clause(ty::ClauseKind::Trait(predicate)) => {
match *predicate.self_ty().kind() {
ty::Param(param_ty) => Ok((
generics.type_param(param_ty, tcx),
predicate.trait_ref.print_only_trait_path().to_string(),
)),
_ => Err(()),
}
}
_ => Err(()),
})
.collect();
if let Ok(predicates) = predicates {
suggest_constraining_type_params(
tcx,
hir_generics,
err,
predicates
.iter()
.map(|(param, constraint)| (param.name.as_str(), &**constraint, None)),
None,
);
}
}
pub(crate) fn report_move_out_while_borrowed(
&mut self,
location: Location,
(place, span): (Place<'tcx>, Span),
borrow: &BorrowData<'tcx>,
) {
debug!(
"report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
location, place, span, borrow
);
let value_msg = self.describe_any_place(place.as_ref());
let borrow_msg = self.describe_any_place(borrow.borrowed_place.as_ref());
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.args_or_use();
let move_spans = self.move_spans(place.as_ref(), location);
let span = move_spans.args_or_use();
let mut err = self.cannot_move_when_borrowed(
span,
borrow_span,
&self.describe_any_place(place.as_ref()),
&borrow_msg,
&value_msg,
);
borrow_spans.var_path_only_subdiag(
self.dcx(),
&mut err,
crate::InitializationRequiringAction::Borrow,
);
move_spans.var_subdiag(self.dcx(), &mut err, None, |kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => MoveUseInCoroutine { var_span },
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
MoveUseInClosure { var_span }
}
}
});
self.explain_why_borrow_contains_point(location, borrow, None)
.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
Some(borrow_span),
None,
);
self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
if let Some(expr) = self.find_expr(borrow_span)
&& let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
{
self.suggest_cloning(&mut err, ty, expr, self.find_expr(span), Some(move_spans));
}
self.buffer_error(err);
}
pub(crate) fn report_use_while_mutably_borrowed(
&self,
location: Location,
(place, _span): (Place<'tcx>, Span),
borrow: &BorrowData<'tcx>,
) -> Diag<'tcx> {
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.args_or_use();
// Conflicting borrows are reported separately, so only check for move
// captures.
let use_spans = self.move_spans(place.as_ref(), location);
let span = use_spans.var_or_use();
// If the attempted use is in a closure then we do not care about the path span of the place we are currently trying to use
// we call `var_span_label` on `borrow_spans` to annotate if the existing borrow was in a closure
let mut err = self.cannot_use_when_mutably_borrowed(
span,
&self.describe_any_place(place.as_ref()),
borrow_span,
&self.describe_any_place(borrow.borrowed_place.as_ref()),
);
borrow_spans.var_subdiag(self.dcx(), &mut err, Some(borrow.kind), |kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
let place = &borrow.borrowed_place;
let desc_place = self.describe_any_place(place.as_ref());
match kind {
hir::ClosureKind::Coroutine(_) => {
BorrowUsePlaceCoroutine { place: desc_place, var_span, is_single_var: true }
}
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
BorrowUsePlaceClosure { place: desc_place, var_span, is_single_var: true }
}
}
});
self.explain_why_borrow_contains_point(location, borrow, None)
.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
None,
None,
);
err
}
pub(crate) fn report_conflicting_borrow(
&self,
location: Location,
(place, span): (Place<'tcx>, Span),
gen_borrow_kind: BorrowKind,
issued_borrow: &BorrowData<'tcx>,
) -> Diag<'tcx> {
let issued_spans = self.retrieve_borrow_spans(issued_borrow);
let issued_span = issued_spans.args_or_use();
let borrow_spans = self.borrow_spans(span, location);
let span = borrow_spans.args_or_use();
let container_name = if issued_spans.for_coroutine() || borrow_spans.for_coroutine() {
"coroutine"
} else {
"closure"
};
let (desc_place, msg_place, msg_borrow, union_type_name) =
self.describe_place_for_conflicting_borrow(place, issued_borrow.borrowed_place);
let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
let second_borrow_desc = if explanation.is_explained() { "second " } else { "" };
// FIXME: supply non-"" `opt_via` when appropriate
let first_borrow_desc;
let mut err = match (gen_borrow_kind, issued_borrow.kind) {
(
BorrowKind::Shared | BorrowKind::Fake(FakeBorrowKind::Deep),
BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
) => {
first_borrow_desc = "mutable ";
let mut err = self.cannot_reborrow_already_borrowed(
span,
&desc_place,
&msg_place,
"immutable",
issued_span,
"it",
"mutable",
&msg_borrow,
None,
);
self.suggest_slice_method_if_applicable(
&mut err,
place,
issued_borrow.borrowed_place,
span,
issued_span,
);
err
}
(
BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
BorrowKind::Shared | BorrowKind::Fake(FakeBorrowKind::Deep),
) => {
first_borrow_desc = "immutable ";
let mut err = self.cannot_reborrow_already_borrowed(
span,
&desc_place,
&msg_place,
"mutable",
issued_span,
"it",
"immutable",
&msg_borrow,
None,
);
self.suggest_slice_method_if_applicable(
&mut err,
place,
issued_borrow.borrowed_place,
span,
issued_span,
);
self.suggest_binding_for_closure_capture_self(&mut err, &issued_spans);
self.suggest_using_closure_argument_instead_of_capture(
&mut err,
issued_borrow.borrowed_place,
&issued_spans,
);
err
}
(
BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
) => {
first_borrow_desc = "first ";
let mut err = self.cannot_mutably_borrow_multiply(
span,
&desc_place,
&msg_place,
issued_span,
&msg_borrow,
None,
);
self.suggest_slice_method_if_applicable(
&mut err,
place,
issued_borrow.borrowed_place,
span,
issued_span,
);
self.suggest_using_closure_argument_instead_of_capture(
&mut err,
issued_borrow.borrowed_place,
&issued_spans,
);
self.explain_iterator_advancement_in_for_loop_if_applicable(
&mut err,
span,
&issued_spans,
);
err
}
(
BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
) => {
first_borrow_desc = "first ";
self.cannot_uniquely_borrow_by_two_closures(span, &desc_place, issued_span, None)
}
(BorrowKind::Mut { .. }, BorrowKind::Fake(FakeBorrowKind::Shallow)) => {
if let Some(immutable_section_description) =
self.classify_immutable_section(issued_borrow.assigned_place)
{
let mut err = self.cannot_mutate_in_immutable_section(
span,
issued_span,
&desc_place,
immutable_section_description,
"mutably borrow",
);
borrow_spans.var_subdiag(
self.dcx(),
&mut err,
Some(BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }),
|kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => BorrowUsePlaceCoroutine {
place: desc_place,
var_span,
is_single_var: true,
},
hir::ClosureKind::Closure
| hir::ClosureKind::CoroutineClosure(_) => BorrowUsePlaceClosure {
place: desc_place,
var_span,
is_single_var: true,
},
}
},
);
return err;
} else {
first_borrow_desc = "immutable ";
self.cannot_reborrow_already_borrowed(
span,
&desc_place,
&msg_place,
"mutable",
issued_span,
"it",
"immutable",
&msg_borrow,
None,
)
}
}
(BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }, _) => {
first_borrow_desc = "first ";
self.cannot_uniquely_borrow_by_one_closure(
span,
container_name,
&desc_place,
"",
issued_span,
"it",
"",
None,
)
}
(
BorrowKind::Shared | BorrowKind::Fake(FakeBorrowKind::Deep),
BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
) => {
first_borrow_desc = "first ";
self.cannot_reborrow_already_uniquely_borrowed(
span,
container_name,
&desc_place,
"",
"immutable",
issued_span,
"",
None,
second_borrow_desc,
)
}
(BorrowKind::Mut { .. }, BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }) => {
first_borrow_desc = "first ";
self.cannot_reborrow_already_uniquely_borrowed(
span,
container_name,
&desc_place,
"",
"mutable",
issued_span,
"",
None,
second_borrow_desc,
)
}
(
BorrowKind::Shared | BorrowKind::Fake(FakeBorrowKind::Deep),
BorrowKind::Shared | BorrowKind::Fake(_),
)
| (
BorrowKind::Fake(FakeBorrowKind::Shallow),
BorrowKind::Mut { .. } | BorrowKind::Shared | BorrowKind::Fake(_),
) => {
unreachable!()
}
};
if issued_spans == borrow_spans {
borrow_spans.var_subdiag(
self.dcx(),
&mut err,
Some(gen_borrow_kind),
|kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => BorrowUsePlaceCoroutine {
place: desc_place,
var_span,
is_single_var: false,
},
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
BorrowUsePlaceClosure {
place: desc_place,
var_span,
is_single_var: false,
}
}
}
},
);
} else {
issued_spans.var_subdiag(
self.dcx(),
&mut err,
Some(issued_borrow.kind),
|kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
let borrow_place = &issued_borrow.borrowed_place;
let borrow_place_desc = self.describe_any_place(borrow_place.as_ref());
match kind {
hir::ClosureKind::Coroutine(_) => {
FirstBorrowUsePlaceCoroutine { place: borrow_place_desc, var_span }
}
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
FirstBorrowUsePlaceClosure { place: borrow_place_desc, var_span }
}
}
},
);
borrow_spans.var_subdiag(
self.dcx(),
&mut err,
Some(gen_borrow_kind),
|kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => {
SecondBorrowUsePlaceCoroutine { place: desc_place, var_span }
}
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
SecondBorrowUsePlaceClosure { place: desc_place, var_span }
}
}
},
);
}
if union_type_name != "" {
err.note(format!(
"{msg_place} is a field of the union `{union_type_name}`, so it overlaps the field {msg_borrow}",
));
}
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
first_borrow_desc,
None,
Some((issued_span, span)),
);
self.suggest_using_local_if_applicable(&mut err, location, issued_borrow, explanation);
self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
err
}
fn suggest_copy_for_type_in_cloned_ref(&self, err: &mut Diag<'tcx>, place: Place<'tcx>) {
let tcx = self.infcx.tcx;
let hir = tcx.hir();
let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
struct FindUselessClone<'tcx> {
tcx: TyCtxt<'tcx>,
typeck_results: &'tcx ty::TypeckResults<'tcx>,
pub clones: Vec<&'tcx hir::Expr<'tcx>>,
}
impl<'tcx> FindUselessClone<'tcx> {
pub fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
Self { tcx, typeck_results: tcx.typeck(def_id), clones: vec![] }
}
}
impl<'tcx> Visitor<'tcx> for FindUselessClone<'tcx> {
fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) {
if let hir::ExprKind::MethodCall(..) = ex.kind
&& let Some(method_def_id) =
self.typeck_results.type_dependent_def_id(ex.hir_id)
&& self.tcx.lang_items().clone_trait() == Some(self.tcx.parent(method_def_id))
{
self.clones.push(ex);
}
hir::intravisit::walk_expr(self, ex);
}
}
let mut expr_finder = FindUselessClone::new(tcx, self.mir_def_id());
let body = hir.body(body_id).value;
expr_finder.visit_expr(body);
pub struct Holds<'tcx> {
ty: Ty<'tcx>,
holds: bool,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Holds<'tcx> {
type Result = std::ops::ControlFlow<()>;
fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
if t == self.ty {
self.holds = true;
}
t.super_visit_with(self)
}
}
let mut types_to_constrain = FxIndexSet::default();
let local_ty = self.body.local_decls[place.local].ty;
let typeck_results = tcx.typeck(self.mir_def_id());
let clone = tcx.require_lang_item(LangItem::Clone, Some(body.span));
for expr in expr_finder.clones {
if let hir::ExprKind::MethodCall(_, rcvr, _, span) = expr.kind
&& let Some(rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id)
&& let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
&& rcvr_ty == ty
&& let ty::Ref(_, inner, _) = rcvr_ty.kind()
&& let inner = inner.peel_refs()
&& let mut v = (Holds { ty: inner, holds: false })
&& let _ = v.visit_ty(local_ty)
&& v.holds
&& let None = self.infcx.type_implements_trait_shallow(clone, inner, self.param_env)
{
err.span_label(
span,
format!(
"this call doesn't do anything, the result is still `{rcvr_ty}` \
because `{inner}` doesn't implement `Clone`",
),
);
types_to_constrain.insert(inner);
}
}
for ty in types_to_constrain {
self.suggest_adding_bounds_or_derive(err, ty, clone, body.span);
}
}
pub(crate) fn suggest_adding_bounds_or_derive(
&self,
err: &mut Diag<'_>,
ty: Ty<'tcx>,
trait_def_id: DefId,
span: Span,
) {
self.suggest_adding_bounds(err, ty, trait_def_id, span);
if let ty::Adt(..) = ty.kind() {
// The type doesn't implement the trait.
let trait_ref =
ty::Binder::dummy(ty::TraitRef::new(self.infcx.tcx, trait_def_id, [ty]));
let obligation = Obligation::new(
self.infcx.tcx,
ObligationCause::dummy(),
self.param_env,
trait_ref,
);
self.infcx.err_ctxt().suggest_derive(
&obligation,
err,
trait_ref.to_predicate(self.infcx.tcx),
);
}
}
#[instrument(level = "debug", skip(self, err))]
fn suggest_using_local_if_applicable(
&self,
err: &mut Diag<'_>,
location: Location,
issued_borrow: &BorrowData<'tcx>,
explanation: BorrowExplanation<'tcx>,
) {
let used_in_call = matches!(
explanation,
BorrowExplanation::UsedLater(LaterUseKind::Call | LaterUseKind::Other, _call_span, _)
);
if !used_in_call {
debug!("not later used in call");
return;
}
let use_span =
if let BorrowExplanation::UsedLater(LaterUseKind::Other, use_span, _) = explanation {
Some(use_span)
} else {
None
};
let outer_call_loc =
if let TwoPhaseActivation::ActivatedAt(loc) = issued_borrow.activation_location {
loc
} else {
issued_borrow.reserve_location
};
let outer_call_stmt = self.body.stmt_at(outer_call_loc);
let inner_param_location = location;
let Some(inner_param_stmt) = self.body.stmt_at(inner_param_location).left() else {
debug!("`inner_param_location` {:?} is not for a statement", inner_param_location);
return;
};
let Some(&inner_param) = inner_param_stmt.kind.as_assign().map(|(p, _)| p) else {
debug!(
"`inner_param_location` {:?} is not for an assignment: {:?}",
inner_param_location, inner_param_stmt
);
return;
};
let inner_param_uses = find_all_local_uses::find(self.body, inner_param.local);
let Some((inner_call_loc, inner_call_term)) =
inner_param_uses.into_iter().find_map(|loc| {
let Either::Right(term) = self.body.stmt_at(loc) else {
debug!("{:?} is a statement, so it can't be a call", loc);
return None;
};
let TerminatorKind::Call { args, .. } = &term.kind else {
debug!("not a call: {:?}", term);
return None;
};
debug!("checking call args for uses of inner_param: {:?}", args);
args.iter()
.map(|a| &a.node)
.any(|a| a == &Operand::Move(inner_param))
.then_some((loc, term))
})
else {
debug!("no uses of inner_param found as a by-move call arg");
return;
};
debug!("===> outer_call_loc = {:?}, inner_call_loc = {:?}", outer_call_loc, inner_call_loc);
let inner_call_span = inner_call_term.source_info.span;
let outer_call_span = match use_span {
Some(span) => span,
None => outer_call_stmt.either(|s| s.source_info, |t| t.source_info).span,
};
if outer_call_span == inner_call_span || !outer_call_span.contains(inner_call_span) {
// FIXME: This stops the suggestion in some cases where it should be emitted.
// Fix the spans for those cases so it's emitted correctly.
debug!(
"outer span {:?} does not strictly contain inner span {:?}",
outer_call_span, inner_call_span
);
return;
}
err.span_help(
inner_call_span,
format!(
"try adding a local storing this{}...",
if use_span.is_some() { "" } else { " argument" }
),
);
err.span_help(
outer_call_span,
format!(
"...and then using that local {}",
if use_span.is_some() { "here" } else { "as the argument to this call" }
),
);
}
pub(crate) fn find_expr(&self, span: Span) -> Option<&hir::Expr<'_>> {
let tcx = self.infcx.tcx;
let body_id = tcx.hir_node(self.mir_hir_id()).body_id()?;
let mut expr_finder = FindExprBySpan::new(span, tcx);
expr_finder.visit_expr(tcx.hir().body(body_id).value);
expr_finder.result
}
fn suggest_slice_method_if_applicable(
&self,
err: &mut Diag<'_>,
place: Place<'tcx>,
borrowed_place: Place<'tcx>,
span: Span,
issued_span: Span,
) {
let tcx = self.infcx.tcx;
let hir = tcx.hir();
let has_split_at_mut = |ty: Ty<'tcx>| {
let ty = ty.peel_refs();
match ty.kind() {
ty::Array(..) | ty::Slice(..) => true,
ty::Adt(def, _) if tcx.get_diagnostic_item(sym::Vec) == Some(def.did()) => true,
_ if ty == tcx.types.str_ => true,
_ => false,
}
};
if let ([ProjectionElem::Index(index1)], [ProjectionElem::Index(index2)])
| (
[ProjectionElem::Deref, ProjectionElem::Index(index1)],
[ProjectionElem::Deref, ProjectionElem::Index(index2)],
) = (&place.projection[..], &borrowed_place.projection[..])
{
let decl1 = &self.body.local_decls[*index1];
let decl2 = &self.body.local_decls[*index2];
let mut note_default_suggestion = || {
err.help(
"consider using `.split_at_mut(position)` or similar method to obtain two \
mutable non-overlapping sub-slices",
)
.help(
"consider using `.swap(index_1, index_2)` to swap elements at the specified \
indices",
);
};
let Some(index1) = self.find_expr(decl1.source_info.span) else {
note_default_suggestion();
return;
};
let Some(index2) = self.find_expr(decl2.source_info.span) else {
note_default_suggestion();
return;
};
let sm = tcx.sess.source_map();
let Ok(index1_str) = sm.span_to_snippet(index1.span) else {
note_default_suggestion();
return;
};
let Ok(index2_str) = sm.span_to_snippet(index2.span) else {
note_default_suggestion();
return;
};
let Some(object) = hir.parent_id_iter(index1.hir_id).find_map(|id| {
if let hir::Node::Expr(expr) = tcx.hir_node(id)
&& let hir::ExprKind::Index(obj, ..) = expr.kind
{
Some(obj)
} else {
None
}
}) else {
note_default_suggestion();
return;
};
let Ok(obj_str) = sm.span_to_snippet(object.span) else {
note_default_suggestion();
return;
};
let Some(swap_call) = hir.parent_id_iter(object.hir_id).find_map(|id| {
if let hir::Node::Expr(call) = tcx.hir_node(id)
&& let hir::ExprKind::Call(callee, ..) = call.kind
&& let hir::ExprKind::Path(qpath) = callee.kind
&& let hir::QPath::Resolved(None, res) = qpath
&& let hir::def::Res::Def(_, did) = res.res
&& tcx.is_diagnostic_item(sym::mem_swap, did)
{
Some(call)
} else {
None
}
}) else {
let hir::Node::Expr(parent) = tcx.parent_hir_node(index1.hir_id) else { return };
let hir::ExprKind::Index(_, idx1, _) = parent.kind else { return };
let hir::Node::Expr(parent) = tcx.parent_hir_node(index2.hir_id) else { return };
let hir::ExprKind::Index(_, idx2, _) = parent.kind else { return };
if !idx1.equivalent_for_indexing(idx2) {
err.help("use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices");
}
return;
};
err.span_suggestion(
swap_call.span,
"use `.swap()` to swap elements at the specified indices instead",
format!("{obj_str}.swap({index1_str}, {index2_str})"),
Applicability::MachineApplicable,
);
return;
}
let place_ty = PlaceRef::ty(&place.as_ref(), self.body, tcx).ty;
let borrowed_place_ty = PlaceRef::ty(&borrowed_place.as_ref(), self.body, tcx).ty;
if !has_split_at_mut(place_ty) && !has_split_at_mut(borrowed_place_ty) {
// Only mention `split_at_mut` on `Vec`, array and slices.
return;
}
let Some(index1) = self.find_expr(span) else { return };
let hir::Node::Expr(parent) = tcx.parent_hir_node(index1.hir_id) else { return };
let hir::ExprKind::Index(_, idx1, _) = parent.kind else { return };
let Some(index2) = self.find_expr(issued_span) else { return };
let hir::Node::Expr(parent) = tcx.parent_hir_node(index2.hir_id) else { return };
let hir::ExprKind::Index(_, idx2, _) = parent.kind else { return };
if idx1.equivalent_for_indexing(idx2) {
// `let a = &mut foo[0]` and `let b = &mut foo[0]`? Don't mention `split_at_mut`
return;
}
err.help("use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices");
}
/// Suggest using `while let` for call `next` on an iterator in a for loop.
///
/// For example:
/// ```ignore (illustrative)
///
/// for x in iter {
/// ...
/// iter.next()
/// }
/// ```
pub(crate) fn explain_iterator_advancement_in_for_loop_if_applicable(
&self,
err: &mut Diag<'_>,
span: Span,
issued_spans: &UseSpans<'tcx>,
) {
let issue_span = issued_spans.args_or_use();
let tcx = self.infcx.tcx;
let hir = tcx.hir();
let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
let typeck_results = tcx.typeck(self.mir_def_id());
struct ExprFinder<'hir> {
issue_span: Span,
expr_span: Span,
body_expr: Option<&'hir hir::Expr<'hir>>,
loop_bind: Option<&'hir Ident>,
loop_span: Option<Span>,
head_span: Option<Span>,
pat_span: Option<Span>,
head: Option<&'hir hir::Expr<'hir>>,
}
impl<'hir> Visitor<'hir> for ExprFinder<'hir> {
fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
// Try to find
// let result = match IntoIterator::into_iter(<head>) {
// mut iter => {
// [opt_ident]: loop {
// match Iterator::next(&mut iter) {
// None => break,
// Some(<pat>) => <body>,
// };
// }
// }
// };
// corresponding to the desugaring of a for loop `for <pat> in <head> { <body> }`.
if let hir::ExprKind::Call(path, [arg]) = ex.kind
&& let hir::ExprKind::Path(hir::QPath::LangItem(LangItem::IntoIterIntoIter, _)) =
path.kind
&& arg.span.contains(self.issue_span)
{
// Find `IntoIterator::into_iter(<head>)`
self.head = Some(arg);
}
if let hir::ExprKind::Loop(
hir::Block { stmts: [stmt, ..], .. },
_,
hir::LoopSource::ForLoop,
_,
) = ex.kind
&& let hir::StmtKind::Expr(hir::Expr {
kind: hir::ExprKind::Match(call, [_, bind, ..], _),
span: head_span,
..
}) = stmt.kind
&& let hir::ExprKind::Call(path, _args) = call.kind
&& let hir::ExprKind::Path(hir::QPath::LangItem(LangItem::IteratorNext, _)) =
path.kind
&& let hir::PatKind::Struct(path, [field, ..], _) = bind.pat.kind
&& let hir::QPath::LangItem(LangItem::OptionSome, pat_span) = path
&& call.span.contains(self.issue_span)
{
// Find `<pat>` and the span for the whole `for` loop.
if let PatField {
pat: hir::Pat { kind: hir::PatKind::Binding(_, _, ident, ..), .. },
..
} = field
{
self.loop_bind = Some(ident);
}
self.head_span = Some(*head_span);
self.pat_span = Some(pat_span);
self.loop_span = Some(stmt.span);
}
if let hir::ExprKind::MethodCall(body_call, recv, ..) = ex.kind
&& body_call.ident.name == sym::next
&& recv.span.source_equal(self.expr_span)
{
self.body_expr = Some(ex);
}
hir::intravisit::walk_expr(self, ex);
}
}
let mut finder = ExprFinder {
expr_span: span,
issue_span,
loop_bind: None,
body_expr: None,
head_span: None,
loop_span: None,
pat_span: None,
head: None,
};
finder.visit_expr(hir.body(body_id).value);
if let Some(body_expr) = finder.body_expr
&& let Some(loop_span) = finder.loop_span
&& let Some(def_id) = typeck_results.type_dependent_def_id(body_expr.hir_id)
&& let Some(trait_did) = tcx.trait_of_item(def_id)
&& tcx.is_diagnostic_item(sym::Iterator, trait_did)
{
if let Some(loop_bind) = finder.loop_bind {
err.note(format!(
"a for loop advances the iterator for you, the result is stored in `{}`",
loop_bind.name,
));
} else {
err.note(
"a for loop advances the iterator for you, the result is stored in its pattern",
);
}
let msg = "if you want to call `next` on a iterator within the loop, consider using \
`while let`";
if let Some(head) = finder.head
&& let Some(pat_span) = finder.pat_span
&& loop_span.contains(body_expr.span)
&& loop_span.contains(head.span)
{
let sm = self.infcx.tcx.sess.source_map();
let mut sugg = vec![];
if let hir::ExprKind::Path(hir::QPath::Resolved(None, _)) = head.kind {
// A bare path doesn't need a `let` assignment, it's already a simple
// binding access.
// As a new binding wasn't added, we don't need to modify the advancing call.
sugg.push((loop_span.with_hi(pat_span.lo()), "while let Some(".to_string()));
sugg.push((
pat_span.shrink_to_hi().with_hi(head.span.lo()),
") = ".to_string(),
));
sugg.push((head.span.shrink_to_hi(), ".next()".to_string()));
} else {
// Needs a new a `let` binding.
let indent = if let Some(indent) = sm.indentation_before(loop_span) {
format!("\n{indent}")
} else {
" ".to_string()
};
let Ok(head_str) = sm.span_to_snippet(head.span) else {
err.help(msg);
return;
};
sugg.push((
loop_span.with_hi(pat_span.lo()),
format!("let iter = {head_str};{indent}while let Some("),
));
sugg.push((
pat_span.shrink_to_hi().with_hi(head.span.hi()),
") = iter.next()".to_string(),
));
// As a new binding was added, we should change how the iterator is advanced to
// use the newly introduced binding.
if let hir::ExprKind::MethodCall(_, recv, ..) = body_expr.kind
&& let hir::ExprKind::Path(hir::QPath::Resolved(None, ..)) = recv.kind
{
// As we introduced a `let iter = <head>;`, we need to change where the
// already borrowed value was accessed from `<recv>.next()` to
// `iter.next()`.
sugg.push((recv.span, "iter".to_string()));
}
}
err.multipart_suggestion(msg, sugg, Applicability::MaybeIncorrect);
} else {
err.help(msg);
}
}
}
/// Suggest using closure argument instead of capture.
///
/// For example:
/// ```ignore (illustrative)
/// struct S;
///
/// impl S {
/// fn call(&mut self, f: impl Fn(&mut Self)) { /* ... */ }
/// fn x(&self) {}
/// }
///
/// let mut v = S;
/// v.call(|this: &mut S| v.x());
/// // ^\ ^-- help: try using the closure argument: `this`
/// // *-- error: cannot borrow `v` as mutable because it is also borrowed as immutable
/// ```
fn suggest_using_closure_argument_instead_of_capture(
&self,
err: &mut Diag<'_>,
borrowed_place: Place<'tcx>,
issued_spans: &UseSpans<'tcx>,
) {
let &UseSpans::ClosureUse { capture_kind_span, .. } = issued_spans else { return };
let tcx = self.infcx.tcx;
let hir = tcx.hir();
// Get the type of the local that we are trying to borrow
let local = borrowed_place.local;
let local_ty = self.body.local_decls[local].ty;
// Get the body the error happens in
let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
let body_expr = hir.body(body_id).value;
struct ClosureFinder<'hir> {
hir: rustc_middle::hir::map::Map<'hir>,
borrow_span: Span,
res: Option<(&'hir hir::Expr<'hir>, &'hir hir::Closure<'hir>)>,
/// The path expression with the `borrow_span` span
error_path: Option<(&'hir hir::Expr<'hir>, &'hir hir::QPath<'hir>)>,
}
impl<'hir> Visitor<'hir> for ClosureFinder<'hir> {
type NestedFilter = OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.hir
}
fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
if let hir::ExprKind::Path(qpath) = &ex.kind
&& ex.span == self.borrow_span
{
self.error_path = Some((ex, qpath));
}
if let hir::ExprKind::Closure(closure) = ex.kind
&& ex.span.contains(self.borrow_span)
// To support cases like `|| { v.call(|this| v.get()) }`
// FIXME: actually support such cases (need to figure out how to move from the capture place to original local)
&& self.res.as_ref().map_or(true, |(prev_res, _)| prev_res.span.contains(ex.span))
{
self.res = Some((ex, closure));
}
hir::intravisit::walk_expr(self, ex);
}
}
// Find the closure that most tightly wraps `capture_kind_span`
let mut finder =
ClosureFinder { hir, borrow_span: capture_kind_span, res: None, error_path: None };
finder.visit_expr(body_expr);
let Some((closure_expr, closure)) = finder.res else { return };
let typeck_results = tcx.typeck(self.mir_def_id());
// Check that the parent of the closure is a method call,
// with receiver matching with local's type (modulo refs)
if let hir::Node::Expr(parent) = tcx.parent_hir_node(closure_expr.hir_id) {
if let hir::ExprKind::MethodCall(_, recv, ..) = parent.kind {
let recv_ty = typeck_results.expr_ty(recv);
if recv_ty.peel_refs() != local_ty {
return;
}
}
}
// Get closure's arguments
let ty::Closure(_, args) = typeck_results.expr_ty(closure_expr).kind() else {
/* hir::Closure can be a coroutine too */
return;
};
let sig = args.as_closure().sig();
let tupled_params = tcx.instantiate_bound_regions_with_erased(
sig.inputs().iter().next().unwrap().map_bound(|&b| b),
);
let ty::Tuple(params) = tupled_params.kind() else { return };
// Find the first argument with a matching type, get its name
let Some((_, this_name)) =
params.iter().zip(hir.body_param_names(closure.body)).find(|(param_ty, name)| {
// FIXME: also support deref for stuff like `Rc` arguments
param_ty.peel_refs() == local_ty && name != &Ident::empty()
})
else {
return;
};
let spans;
if let Some((_path_expr, qpath)) = finder.error_path
&& let hir::QPath::Resolved(_, path) = qpath
&& let hir::def::Res::Local(local_id) = path.res
{
// Find all references to the problematic variable in this closure body
struct VariableUseFinder {
local_id: hir::HirId,
spans: Vec<Span>,
}
impl<'hir> Visitor<'hir> for VariableUseFinder {
fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
if let hir::ExprKind::Path(qpath) = &ex.kind
&& let hir::QPath::Resolved(_, path) = qpath
&& let hir::def::Res::Local(local_id) = path.res
&& local_id == self.local_id
{
self.spans.push(ex.span);
}
hir::intravisit::walk_expr(self, ex);
}
}
let mut finder = VariableUseFinder { local_id, spans: Vec::new() };
finder.visit_expr(hir.body(closure.body).value);
spans = finder.spans;
} else {
spans = vec![capture_kind_span];
}
err.multipart_suggestion(
"try using the closure argument",
iter::zip(spans, iter::repeat(this_name.to_string())).collect(),
Applicability::MaybeIncorrect,
);
}
fn suggest_binding_for_closure_capture_self(
&self,
err: &mut Diag<'_>,
issued_spans: &UseSpans<'tcx>,
) {
let UseSpans::ClosureUse { capture_kind_span, .. } = issued_spans else { return };
struct ExpressionFinder<'tcx> {
capture_span: Span,
closure_change_spans: Vec<Span>,
closure_arg_span: Option<Span>,
in_closure: bool,
suggest_arg: String,
tcx: TyCtxt<'tcx>,
closure_local_id: Option<hir::HirId>,
closure_call_changes: Vec<(Span, String)>,
}
impl<'hir> Visitor<'hir> for ExpressionFinder<'hir> {
fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
if e.span.contains(self.capture_span) {
if let hir::ExprKind::Closure(&hir::Closure {
kind: hir::ClosureKind::Closure,
body,
fn_arg_span,
fn_decl: hir::FnDecl { inputs, .. },
..
}) = e.kind
&& let hir::Node::Expr(body) = self.tcx.hir_node(body.hir_id)
{
self.suggest_arg = "this: &Self".to_string();
if inputs.len() > 0 {
self.suggest_arg.push_str(", ");
}
self.in_closure = true;
self.closure_arg_span = fn_arg_span;
self.visit_expr(body);
self.in_closure = false;
}
}
if let hir::Expr { kind: hir::ExprKind::Path(path), .. } = e {
if let hir::QPath::Resolved(_, hir::Path { segments: [seg], .. }) = path
&& seg.ident.name == kw::SelfLower
&& self.in_closure
{
self.closure_change_spans.push(e.span);
}
}
hir::intravisit::walk_expr(self, e);
}
fn visit_local(&mut self, local: &'hir hir::LetStmt<'hir>) {
if let hir::Pat { kind: hir::PatKind::Binding(_, hir_id, _ident, _), .. } =
local.pat
&& let Some(init) = local.init
{
if let hir::Expr {
kind:
hir::ExprKind::Closure(&hir::Closure {
kind: hir::ClosureKind::Closure,
..
}),
..
} = init
&& init.span.contains(self.capture_span)
{
self.closure_local_id = Some(*hir_id);
}
}
hir::intravisit::walk_local(self, local);
}
fn visit_stmt(&mut self, s: &'hir hir::Stmt<'hir>) {
if let hir::StmtKind::Semi(e) = s.kind
&& let hir::ExprKind::Call(
hir::Expr { kind: hir::ExprKind::Path(path), .. },
args,
) = e.kind
&& let hir::QPath::Resolved(_, hir::Path { segments: [seg], .. }) = path
&& let Res::Local(hir_id) = seg.res
&& Some(hir_id) == self.closure_local_id
{
let (span, arg_str) = if args.len() > 0 {
(args[0].span.shrink_to_lo(), "self, ".to_string())
} else {
let span = e.span.trim_start(seg.ident.span).unwrap_or(e.span);
(span, "(self)".to_string())
};
self.closure_call_changes.push((span, arg_str));
}
hir::intravisit::walk_stmt(self, s);
}
}
if let hir::Node::ImplItem(hir::ImplItem {
kind: hir::ImplItemKind::Fn(_fn_sig, body_id),
..
}) = self.infcx.tcx.hir_node(self.mir_hir_id())
&& let hir::Node::Expr(expr) = self.infcx.tcx.hir_node(body_id.hir_id)
{
let mut finder = ExpressionFinder {
capture_span: *capture_kind_span,
closure_change_spans: vec![],
closure_arg_span: None,
in_closure: false,
suggest_arg: String::new(),
closure_local_id: None,
closure_call_changes: vec![],
tcx: self.infcx.tcx,
};
finder.visit_expr(expr);
if finder.closure_change_spans.is_empty() || finder.closure_call_changes.is_empty() {
return;
}
let mut sugg = vec![];
let sm = self.infcx.tcx.sess.source_map();
if let Some(span) = finder.closure_arg_span {
sugg.push((sm.next_point(span.shrink_to_lo()).shrink_to_hi(), finder.suggest_arg));
}
for span in finder.closure_change_spans {
sugg.push((span, "this".to_string()));
}
for (span, suggest) in finder.closure_call_changes {
sugg.push((span, suggest));
}
err.multipart_suggestion_verbose(
"try explicitly pass `&Self` into the Closure as an argument",
sugg,
Applicability::MachineApplicable,
);
}
}
/// Returns the description of the root place for a conflicting borrow and the full
/// descriptions of the places that caused the conflict.
///
/// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
/// attempted while a shared borrow is live, then this function will return:
/// ```
/// ("x", "", "")
/// # ;
/// ```
/// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
/// a shared borrow of another field `x.y`, then this function will return:
/// ```
/// ("x", "x.z", "x.y")
/// # ;
/// ```
/// In the more complex union case, where the union is a field of a struct, then if a mutable
/// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
/// another field `x.u.y`, then this function will return:
/// ```
/// ("x.u", "x.u.z", "x.u.y")
/// # ;
/// ```
/// This is used when creating error messages like below:
///
/// ```text
/// cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
/// mutable (via `a.u.s.b`) [E0502]
/// ```
pub(crate) fn describe_place_for_conflicting_borrow(
&self,
first_borrowed_place: Place<'tcx>,
second_borrowed_place: Place<'tcx>,
) -> (String, String, String, String) {
// Define a small closure that we can use to check if the type of a place
// is a union.
let union_ty = |place_base| {
// Need to use fn call syntax `PlaceRef::ty` to determine the type of `place_base`;
// using a type annotation in the closure argument instead leads to a lifetime error.
let ty = PlaceRef::ty(&place_base, self.body, self.infcx.tcx).ty;
ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
};
// Start with an empty tuple, so we can use the functions on `Option` to reduce some
// code duplication (particularly around returning an empty description in the failure
// case).
Some(())
.filter(|_| {
// If we have a conflicting borrow of the same place, then we don't want to add
// an extraneous "via x.y" to our diagnostics, so filter out this case.
first_borrowed_place != second_borrowed_place
})
.and_then(|_| {
// We're going to want to traverse the first borrowed place to see if we can find
// field access to a union. If we find that, then we will keep the place of the
// union being accessed and the field that was being accessed so we can check the
// second borrowed place for the same union and an access to a different field.
for (place_base, elem) in first_borrowed_place.iter_projections().rev() {
match elem {
ProjectionElem::Field(field, _) if union_ty(place_base).is_some() => {
return Some((place_base, field));
}
_ => {}
}
}
None
})
.and_then(|(target_base, target_field)| {
// With the place of a union and a field access into it, we traverse the second
// borrowed place and look for an access to a different field of the same union.
for (place_base, elem) in second_borrowed_place.iter_projections().rev() {
if let ProjectionElem::Field(field, _) = elem {
if let Some(union_ty) = union_ty(place_base) {
if field != target_field && place_base == target_base {
return Some((
self.describe_any_place(place_base),
self.describe_any_place(first_borrowed_place.as_ref()),
self.describe_any_place(second_borrowed_place.as_ref()),
union_ty.to_string(),
));
}
}
}
}
None
})
.unwrap_or_else(|| {
// If we didn't find a field access into a union, or both places match, then
// only return the description of the first place.
(
self.describe_any_place(first_borrowed_place.as_ref()),
"".to_string(),
"".to_string(),
"".to_string(),
)
})
}
/// This means that some data referenced by `borrow` needs to live
/// past the point where the StorageDeadOrDrop of `place` occurs.
/// This is usually interpreted as meaning that `place` has too
/// short a lifetime. (But sometimes it is more useful to report
/// it as a more direct conflict between the execution of a
/// `Drop::drop` with an aliasing borrow.)
#[instrument(level = "debug", skip(self))]
pub(crate) fn report_borrowed_value_does_not_live_long_enough(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
place_span: (Place<'tcx>, Span),
kind: Option<WriteKind>,
) {
let drop_span = place_span.1;
let borrowed_local = borrow.borrowed_place.local;
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.var_or_use_path_span();
let proper_span = self.body.local_decls[borrowed_local].source_info.span;
if self.access_place_error_reported.contains(&(Place::from(borrowed_local), borrow_span)) {
debug!(
"suppressing access_place error when borrow doesn't live long enough for {:?}",
borrow_span
);
return;
}
self.access_place_error_reported.insert((Place::from(borrowed_local), borrow_span));
if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
let err =
self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
self.buffer_error(err);
return;
}
if let StorageDeadOrDrop::Destructor(dropped_ty) =
self.classify_drop_access_kind(borrow.borrowed_place.as_ref())
{
// If a borrow of path `B` conflicts with drop of `D` (and
// we're not in the uninteresting case where `B` is a
// prefix of `D`), then report this as a more interesting
// destructor conflict.
if !borrow.borrowed_place.as_ref().is_prefix_of(place_span.0.as_ref()) {
self.report_borrow_conflicts_with_destructor(
location, borrow, place_span, kind, dropped_ty,
);
return;
}
}
let place_desc = self.describe_place(borrow.borrowed_place.as_ref());
let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
let explanation = self.explain_why_borrow_contains_point(location, borrow, kind_place);
debug!(?place_desc, ?explanation);
let err = match (place_desc, explanation) {
// If the outlives constraint comes from inside the closure,
// for example:
//
// let x = 0;
// let y = &x;
// Box::new(|| y) as Box<Fn() -> &'static i32>
//
// then just use the normal error. The closure isn't escaping
// and `move` will not help here.
(
Some(name),
BorrowExplanation::UsedLater(LaterUseKind::ClosureCapture, var_or_use_span, _),
) if borrow_spans.for_coroutine() || borrow_spans.for_closure() => self
.report_escaping_closure_capture(
borrow_spans,
borrow_span,
&RegionName {
name: self.synthesize_region_name(),
source: RegionNameSource::Static,
},
ConstraintCategory::CallArgument(None),
var_or_use_span,
&format!("`{name}`"),
"block",
),
(
Some(name),
BorrowExplanation::MustBeValidFor {
category:
category @ (ConstraintCategory::Return(_)
| ConstraintCategory::CallArgument(_)
| ConstraintCategory::OpaqueType),
from_closure: false,
ref region_name,
span,
..
},
) if borrow_spans.for_coroutine() || borrow_spans.for_closure() => self
.report_escaping_closure_capture(
borrow_spans,
borrow_span,
region_name,
category,
span,
&format!("`{name}`"),
"function",
),
(
name,
BorrowExplanation::MustBeValidFor {
category: ConstraintCategory::Assignment,
from_closure: false,
region_name:
RegionName {
source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name),
..
},
span,
..
},
) => self.report_escaping_data(borrow_span, &name, upvar_span, upvar_name, span),
(Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
location,
&name,
borrow,
drop_span,
borrow_spans,
explanation,
),
(None, explanation) => self.report_temporary_value_does_not_live_long_enough(
location,
borrow,
drop_span,
borrow_spans,
proper_span,
explanation,
),
};
self.buffer_error(err);
}
fn report_local_value_does_not_live_long_enough(
&self,
location: Location,
name: &str,
borrow: &BorrowData<'tcx>,
drop_span: Span,
borrow_spans: UseSpans<'tcx>,
explanation: BorrowExplanation<'tcx>,
) -> Diag<'tcx> {
debug!(
"report_local_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}, {:?}\
)",
location, name, borrow, drop_span, borrow_spans
);
let borrow_span = borrow_spans.var_or_use_path_span();
if let BorrowExplanation::MustBeValidFor {
category,
span,
ref opt_place_desc,
from_closure: false,
..
} = explanation
{
if let Some(diag) = self.try_report_cannot_return_reference_to_local(
borrow,
borrow_span,
span,
category,
opt_place_desc.as_ref(),
) {
return diag;
}
}
let mut err = self.path_does_not_live_long_enough(borrow_span, &format!("`{name}`"));
if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
let region_name = annotation.emit(self, &mut err);
err.span_label(
borrow_span,
format!("`{name}` would have to be valid for `{region_name}`..."),
);
err.span_label(
drop_span,
format!(
"...but `{}` will be dropped here, when the {} returns",
name,
self.infcx
.tcx
.opt_item_name(self.mir_def_id().to_def_id())
.map(|name| format!("function `{name}`"))
.unwrap_or_else(|| {
match &self.infcx.tcx.def_kind(self.mir_def_id()) {
DefKind::Closure
if self
.infcx
.tcx
.is_coroutine(self.mir_def_id().to_def_id()) =>
{
"enclosing coroutine"
}
DefKind::Closure => "enclosing closure",
kind => bug!("expected closure or coroutine, found {:?}", kind),
}
.to_string()
})
),
);
err.note(
"functions cannot return a borrow to data owned within the function's scope, \
functions can only return borrows to data passed as arguments",
);
err.note(
"to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
references-and-borrowing.html#dangling-references>",
);
if let BorrowExplanation::MustBeValidFor { .. } = explanation {
} else {
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
None,
None,
);
}
} else {
err.span_label(borrow_span, "borrowed value does not live long enough");
err.span_label(drop_span, format!("`{name}` dropped here while still borrowed"));
borrow_spans.args_subdiag(self.dcx(), &mut err, |args_span| {
crate::session_diagnostics::CaptureArgLabel::Capture {
is_within: borrow_spans.for_coroutine(),
args_span,
}
});
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
Some(borrow_span),
None,
);
}
err
}
fn report_borrow_conflicts_with_destructor(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
(place, drop_span): (Place<'tcx>, Span),
kind: Option<WriteKind>,
dropped_ty: Ty<'tcx>,
) {
debug!(
"report_borrow_conflicts_with_destructor(\
{:?}, {:?}, ({:?}, {:?}), {:?}\
)",
location, borrow, place, drop_span, kind,
);
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.var_or_use();
let mut err = self.cannot_borrow_across_destructor(borrow_span);
let what_was_dropped = match self.describe_place(place.as_ref()) {
Some(name) => format!("`{name}`"),
None => String::from("temporary value"),
};
let label = match self.describe_place(borrow.borrowed_place.as_ref()) {
Some(borrowed) => format!(
"here, drop of {what_was_dropped} needs exclusive access to `{borrowed}`, \
because the type `{dropped_ty}` implements the `Drop` trait"
),
None => format!(
"here is drop of {what_was_dropped}; whose type `{dropped_ty}` implements the `Drop` trait"
),
};
err.span_label(drop_span, label);
// Only give this note and suggestion if they could be relevant.
let explanation =
self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
match explanation {
BorrowExplanation::UsedLater { .. }
| BorrowExplanation::UsedLaterWhenDropped { .. } => {
err.note("consider using a `let` binding to create a longer lived value");
}
_ => {}
}
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
None,
None,
);
self.buffer_error(err);
}
fn report_thread_local_value_does_not_live_long_enough(
&self,
drop_span: Span,
borrow_span: Span,
) -> Diag<'tcx> {
debug!(
"report_thread_local_value_does_not_live_long_enough(\
{:?}, {:?}\
)",
drop_span, borrow_span
);
self.thread_local_value_does_not_live_long_enough(borrow_span)
.with_span_label(
borrow_span,
"thread-local variables cannot be borrowed beyond the end of the function",
)
.with_span_label(drop_span, "end of enclosing function is here")
}
#[instrument(level = "debug", skip(self))]
fn report_temporary_value_does_not_live_long_enough(
&self,
location: Location,
borrow: &BorrowData<'tcx>,
drop_span: Span,
borrow_spans: UseSpans<'tcx>,
proper_span: Span,
explanation: BorrowExplanation<'tcx>,
) -> Diag<'tcx> {
if let BorrowExplanation::MustBeValidFor { category, span, from_closure: false, .. } =
explanation
{
if let Some(diag) = self.try_report_cannot_return_reference_to_local(
borrow,
proper_span,
span,
category,
None,
) {
return diag;
}
}
let mut err = self.temporary_value_borrowed_for_too_long(proper_span);
err.span_label(proper_span, "creates a temporary value which is freed while still in use");
err.span_label(drop_span, "temporary value is freed at the end of this statement");
match explanation {
BorrowExplanation::UsedLater(..)
| BorrowExplanation::UsedLaterInLoop(..)
| BorrowExplanation::UsedLaterWhenDropped { .. } => {
// Only give this note and suggestion if it could be relevant.
let sm = self.infcx.tcx.sess.source_map();
let mut suggested = false;
let msg = "consider using a `let` binding to create a longer lived value";
/// We check that there's a single level of block nesting to ensure always correct
/// suggestions. If we don't, then we only provide a free-form message to avoid
/// misleading users in cases like `tests/ui/nll/borrowed-temporary-error.rs`.
/// We could expand the analysis to suggest hoising all of the relevant parts of
/// the users' code to make the code compile, but that could be too much.
/// We found the `prop_expr` by the way to check whether the expression is a `FormatArguments`,
/// which is a special case since it's generated by the compiler.
struct NestedStatementVisitor<'tcx> {
span: Span,
current: usize,
found: usize,
prop_expr: Option<&'tcx hir::Expr<'tcx>>,
call: Option<&'tcx hir::Expr<'tcx>>,
}
impl<'tcx> Visitor<'tcx> for NestedStatementVisitor<'tcx> {
fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
self.current += 1;
walk_block(self, block);
self.current -= 1;
}
fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
if let hir::ExprKind::MethodCall(_, rcvr, _, _) = expr.kind {
if self.span == rcvr.span.source_callsite() {
self.call = Some(expr);
}
}
if self.span == expr.span.source_callsite() {
self.found = self.current;
if self.prop_expr.is_none() {
self.prop_expr = Some(expr);
}
}
walk_expr(self, expr);
}
}
let source_info = self.body.source_info(location);
let proper_span = proper_span.source_callsite();
if let Some(scope) = self.body.source_scopes.get(source_info.scope)
&& let ClearCrossCrate::Set(scope_data) = &scope.local_data
&& let Some(id) = self.infcx.tcx.hir_node(scope_data.lint_root).body_id()
&& let hir::ExprKind::Block(block, _) = self.infcx.tcx.hir().body(id).value.kind
{
for stmt in block.stmts {
let mut visitor = NestedStatementVisitor {
span: proper_span,
current: 0,
found: 0,
prop_expr: None,
call: None,
};
visitor.visit_stmt(stmt);
let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
let expr_ty: Option<Ty<'_>> =
visitor.prop_expr.map(|expr| typeck_results.expr_ty(expr).peel_refs());
let is_format_arguments_item = if let Some(expr_ty) = expr_ty
&& let ty::Adt(adt, _) = expr_ty.kind()
{
self.infcx.tcx.lang_items().get(LangItem::FormatArguments)
== Some(adt.did())
} else {
false
};
if visitor.found == 0
&& stmt.span.contains(proper_span)
&& let Some(p) = sm.span_to_margin(stmt.span)
&& let Ok(s) = sm.span_to_snippet(proper_span)
{
if let Some(call) = visitor.call
&& let hir::ExprKind::MethodCall(path, _, [], _) = call.kind
&& path.ident.name == sym::iter
&& let Some(ty) = expr_ty
{
err.span_suggestion_verbose(
path.ident.span,
format!(
"consider consuming the `{ty}` when turning it into an \
`Iterator`",
),
"into_iter",
Applicability::MaybeIncorrect,
);
}
if !is_format_arguments_item {
let addition = format!("let binding = {};\n{}", s, " ".repeat(p));
err.multipart_suggestion_verbose(
msg,
vec![
(stmt.span.shrink_to_lo(), addition),
(proper_span, "binding".to_string()),
],
Applicability::MaybeIncorrect,
);
} else {
err.note("the result of `format_args!` can only be assigned directly if no placeholders in its arguments are used");
err.note("to learn more, visit <https://doc.rust-lang.org/std/macro.format_args.html>");
}
suggested = true;
break;
}
}
}
if !suggested {
err.note(msg);
}
}
_ => {}
}
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
None,
None,
);
borrow_spans.args_subdiag(self.dcx(), &mut err, |args_span| {
crate::session_diagnostics::CaptureArgLabel::Capture {
is_within: borrow_spans.for_coroutine(),
args_span,
}
});
err
}
fn try_report_cannot_return_reference_to_local(
&self,
borrow: &BorrowData<'tcx>,
borrow_span: Span,
return_span: Span,
category: ConstraintCategory<'tcx>,
opt_place_desc: Option<&String>,
) -> Option<Diag<'tcx>> {
let return_kind = match category {
ConstraintCategory::Return(_) => "return",
ConstraintCategory::Yield => "yield",
_ => return None,
};
// FIXME use a better heuristic than Spans
let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
"reference to"
} else {
"value referencing"
};
let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
let local_kind = if let Some(local) = borrow.borrowed_place.as_local() {
match self.body.local_kind(local) {
LocalKind::Temp if self.body.local_decls[local].is_user_variable() => {
"local variable "
}
LocalKind::Arg
if !self.upvars.is_empty() && local == ty::CAPTURE_STRUCT_LOCAL =>
{
"variable captured by `move` "
}
LocalKind::Arg => "function parameter ",
LocalKind::ReturnPointer | LocalKind::Temp => {
bug!("temporary or return pointer with a name")
}
}
} else {
"local data "
};
(format!("{local_kind}`{place_desc}`"), format!("`{place_desc}` is borrowed here"))
} else {
let local = borrow.borrowed_place.local;
match self.body.local_kind(local) {
LocalKind::Arg => (
"function parameter".to_string(),
"function parameter borrowed here".to_string(),
),
LocalKind::Temp if self.body.local_decls[local].is_user_variable() => {
("local binding".to_string(), "local binding introduced here".to_string())
}
LocalKind::ReturnPointer | LocalKind::Temp => {
("temporary value".to_string(), "temporary value created here".to_string())
}
}
};
let mut err = self.cannot_return_reference_to_local(
return_span,
return_kind,
reference_desc,
&place_desc,
);
if return_span != borrow_span {
err.span_label(borrow_span, note);
let tcx = self.infcx.tcx;
let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
// to avoid panics
if let Some(iter_trait) = tcx.get_diagnostic_item(sym::Iterator)
&& self
.infcx
.type_implements_trait(iter_trait, [return_ty], self.param_env)
.must_apply_modulo_regions()
{
err.span_suggestion_hidden(
return_span.shrink_to_hi(),
"use `.collect()` to allocate the iterator",
".collect::<Vec<_>>()",
Applicability::MaybeIncorrect,
);
}
}
Some(err)
}
#[instrument(level = "debug", skip(self))]
fn report_escaping_closure_capture(
&self,
use_span: UseSpans<'tcx>,
var_span: Span,
fr_name: &RegionName,
category: ConstraintCategory<'tcx>,
constraint_span: Span,
captured_var: &str,
scope: &str,
) -> Diag<'tcx> {
let tcx = self.infcx.tcx;
let args_span = use_span.args_or_use();
let (sugg_span, suggestion) = match tcx.sess.source_map().span_to_snippet(args_span) {
Ok(string) => {
let coro_prefix = if string.starts_with("async") {
// `async` is 5 chars long. Not using `.len()` to avoid the cast from `usize` to `u32`
Some(5)
} else if string.starts_with("gen") {
// `gen` is 3 chars long
Some(3)
} else {
None
};
if let Some(n) = coro_prefix {
let pos = args_span.lo() + BytePos(n);
(args_span.with_lo(pos).with_hi(pos), " move")
} else {
(args_span.shrink_to_lo(), "move ")
}
}
Err(_) => (args_span, "move |<args>| <body>"),
};
let kind = match use_span.coroutine_kind() {
Some(coroutine_kind) => match coroutine_kind {
CoroutineKind::Desugared(CoroutineDesugaring::Gen, kind) => match kind {
CoroutineSource::Block => "gen block",
CoroutineSource::Closure => "gen closure",
CoroutineSource::Fn => {
bug!("gen block/closure expected, but gen function found.")
}
},
CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, kind) => match kind {
CoroutineSource::Block => "async gen block",
CoroutineSource::Closure => "async gen closure",
CoroutineSource::Fn => {
bug!("gen block/closure expected, but gen function found.")
}
},
CoroutineKind::Desugared(CoroutineDesugaring::Async, async_kind) => {
match async_kind {
CoroutineSource::Block => "async block",
CoroutineSource::Closure => "async closure",
CoroutineSource::Fn => {
bug!("async block/closure expected, but async function found.")
}
}
}
CoroutineKind::Coroutine(_) => "coroutine",
},
None => "closure",
};
let mut err = self.cannot_capture_in_long_lived_closure(
args_span,
kind,
captured_var,
var_span,
scope,
);
err.span_suggestion_verbose(
sugg_span,
format!(
"to force the {kind} to take ownership of {captured_var} (and any \
other referenced variables), use the `move` keyword"
),
suggestion,
Applicability::MachineApplicable,
);
match category {
ConstraintCategory::Return(_) | ConstraintCategory::OpaqueType => {
let msg = format!("{kind} is returned here");
err.span_note(constraint_span, msg);
}
ConstraintCategory::CallArgument(_) => {
fr_name.highlight_region_name(&mut err);
if matches!(
use_span.coroutine_kind(),
Some(CoroutineKind::Desugared(CoroutineDesugaring::Async, _))
) {
err.note(
"async blocks are not executed immediately and must either take a \
reference or ownership of outside variables they use",
);
} else {
let msg = format!("{scope} requires argument type to outlive `{fr_name}`");
err.span_note(constraint_span, msg);
}
}
_ => bug!(
"report_escaping_closure_capture called with unexpected constraint \
category: `{:?}`",
category
),
}
err
}
fn report_escaping_data(
&self,
borrow_span: Span,
name: &Option<String>,
upvar_span: Span,
upvar_name: Symbol,
escape_span: Span,
) -> Diag<'tcx> {
let tcx = self.infcx.tcx;
let escapes_from = tcx.def_descr(self.mir_def_id().to_def_id());
let mut err =
borrowck_errors::borrowed_data_escapes_closure(tcx, escape_span, escapes_from);
err.span_label(
upvar_span,
format!("`{upvar_name}` declared here, outside of the {escapes_from} body"),
);
err.span_label(borrow_span, format!("borrow is only valid in the {escapes_from} body"));
if let Some(name) = name {
err.span_label(
escape_span,
format!("reference to `{name}` escapes the {escapes_from} body here"),
);
} else {
err.span_label(escape_span, format!("reference escapes the {escapes_from} body here"));
}
err
}
fn get_moved_indexes(
&self,
location: Location,
mpi: MovePathIndex,
) -> (Vec<MoveSite>, Vec<Location>) {
fn predecessor_locations<'tcx, 'a>(
body: &'a mir::Body<'tcx>,
location: Location,
) -> impl Iterator<Item = Location> + Captures<'tcx> + 'a {
if location.statement_index == 0 {
let predecessors = body.basic_blocks.predecessors()[location.block].to_vec();
Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
} else {
Either::Right(std::iter::once(Location {
statement_index: location.statement_index - 1,
..location
}))
}
}
let mut mpis = vec![mpi];
let move_paths = &self.move_data.move_paths;
mpis.extend(move_paths[mpi].parents(move_paths).map(|(mpi, _)| mpi));
let mut stack = Vec::new();
let mut back_edge_stack = Vec::new();
predecessor_locations(self.body, location).for_each(|predecessor| {
if location.dominates(predecessor, self.dominators()) {
back_edge_stack.push(predecessor)
} else {
stack.push(predecessor);
}
});
let mut reached_start = false;
/* Check if the mpi is initialized as an argument */
let mut is_argument = false;
for arg in self.body.args_iter() {
if let Some(path) = self.move_data.rev_lookup.find_local(arg) {
if mpis.contains(&path) {
is_argument = true;
}
}
}
let mut visited = FxIndexSet::default();
let mut move_locations = FxIndexSet::default();
let mut reinits = vec![];
let mut result = vec![];
let mut dfs_iter = |result: &mut Vec<MoveSite>, location: Location, is_back_edge: bool| {
debug!(
"report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
location, is_back_edge
);
if !visited.insert(location) {
return true;
}
// check for moves
let stmt_kind =
self.body[location.block].statements.get(location.statement_index).map(|s| &s.kind);
if let Some(StatementKind::StorageDead(..)) = stmt_kind {
// this analysis only tries to find moves explicitly
// written by the user, so we ignore the move-outs
// created by `StorageDead` and at the beginning
// of a function.
} else {
// If we are found a use of a.b.c which was in error, then we want to look for
// moves not only of a.b.c but also a.b and a.
//
// Note that the moves data already includes "parent" paths, so we don't have to
// worry about the other case: that is, if there is a move of a.b.c, it is already
// marked as a move of a.b and a as well, so we will generate the correct errors
// there.
for moi in &self.move_data.loc_map[location] {
debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
let path = self.move_data.moves[*moi].path;
if mpis.contains(&path) {
debug!(
"report_use_of_moved_or_uninitialized: found {:?}",
move_paths[path].place
);
result.push(MoveSite { moi: *moi, traversed_back_edge: is_back_edge });
move_locations.insert(location);
// Strictly speaking, we could continue our DFS here. There may be
// other moves that can reach the point of error. But it is kind of
// confusing to highlight them.
//
// Example:
//
// ```
// let a = vec![];
// let b = a;
// let c = a;
// drop(a); // <-- current point of error
// ```
//
// Because we stop the DFS here, we only highlight `let c = a`,
// and not `let b = a`. We will of course also report an error at
// `let c = a` which highlights `let b = a` as the move.
return true;
}
}
}
// check for inits
let mut any_match = false;
for ii in &self.move_data.init_loc_map[location] {
let init = self.move_data.inits[*ii];
match init.kind {
InitKind::Deep | InitKind::NonPanicPathOnly => {
if mpis.contains(&init.path) {
any_match = true;
}
}
InitKind::Shallow => {
if mpi == init.path {
any_match = true;
}
}
}
}
if any_match {
reinits.push(location);
return true;
}
return false;
};
while let Some(location) = stack.pop() {
if dfs_iter(&mut result, location, false) {
continue;
}
let mut has_predecessor = false;
predecessor_locations(self.body, location).for_each(|predecessor| {
if location.dominates(predecessor, self.dominators()) {
back_edge_stack.push(predecessor)
} else {
stack.push(predecessor);
}
has_predecessor = true;
});
if !has_predecessor {
reached_start = true;
}
}
if (is_argument || !reached_start) && result.is_empty() {
/* Process back edges (moves in future loop iterations) only if
the move path is definitely initialized upon loop entry,
to avoid spurious "in previous iteration" errors.
During DFS, if there's a path from the error back to the start
of the function with no intervening init or move, then the
move path may be uninitialized at loop entry.
*/
while let Some(location) = back_edge_stack.pop() {
if dfs_iter(&mut result, location, true) {
continue;
}
predecessor_locations(self.body, location)
.for_each(|predecessor| back_edge_stack.push(predecessor));
}
}
// Check if we can reach these reinits from a move location.
let reinits_reachable = reinits
.into_iter()
.filter(|reinit| {
let mut visited = FxIndexSet::default();
let mut stack = vec![*reinit];
while let Some(location) = stack.pop() {
if !visited.insert(location) {
continue;
}
if move_locations.contains(&location) {
return true;
}
stack.extend(predecessor_locations(self.body, location));
}
false
})
.collect::<Vec<Location>>();
(result, reinits_reachable)
}
pub(crate) fn report_illegal_mutation_of_borrowed(
&mut self,
location: Location,
(place, span): (Place<'tcx>, Span),
loan: &BorrowData<'tcx>,
) {
let loan_spans = self.retrieve_borrow_spans(loan);
let loan_span = loan_spans.args_or_use();
let descr_place = self.describe_any_place(place.as_ref());
if let BorrowKind::Fake(_) = loan.kind {
if let Some(section) = self.classify_immutable_section(loan.assigned_place) {
let mut err = self.cannot_mutate_in_immutable_section(
span,
loan_span,
&descr_place,
section,
"assign",
);
loan_spans.var_subdiag(self.dcx(), &mut err, Some(loan.kind), |kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
BorrowUseInClosure { var_span }
}
}
});
self.buffer_error(err);
return;
}
}
let mut err = self.cannot_assign_to_borrowed(span, loan_span, &descr_place);
loan_spans.var_subdiag(self.dcx(), &mut err, Some(loan.kind), |kind, var_span| {
use crate::session_diagnostics::CaptureVarCause::*;
match kind {
hir::ClosureKind::Coroutine(_) => BorrowUseInCoroutine { var_span },
hir::ClosureKind::Closure | hir::ClosureKind::CoroutineClosure(_) => {
BorrowUseInClosure { var_span }
}
}
});
self.explain_why_borrow_contains_point(location, loan, None).add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&self.local_names,
&mut err,
"",
None,
None,
);
self.explain_deref_coercion(loan, &mut err);
self.buffer_error(err);
}
fn explain_deref_coercion(&mut self, loan: &BorrowData<'tcx>, err: &mut Diag<'_>) {
let tcx = self.infcx.tcx;
if let (
Some(Terminator {
kind: TerminatorKind::Call { call_source: CallSource::OverloadedOperator, .. },
..
}),
Some((method_did, method_args)),
) = (
&self.body[loan.reserve_location.block].terminator,
rustc_middle::util::find_self_call(
tcx,
self.body,
loan.assigned_place.local,
loan.reserve_location.block,
),
) {
if tcx.is_diagnostic_item(sym::deref_method, method_did) {
let deref_target =
tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
Instance::resolve(tcx, self.param_env, deref_target, method_args)
.transpose()
});
if let Some(Ok(instance)) = deref_target {
let deref_target_ty = instance.ty(tcx, self.param_env);
err.note(format!("borrow occurs due to deref coercion to `{deref_target_ty}`"));
err.span_note(tcx.def_span(instance.def_id()), "deref defined here");
}
}
}
}
/// Reports an illegal reassignment; for example, an assignment to
/// (part of) a non-`mut` local that occurs potentially after that
/// local has already been initialized. `place` is the path being
/// assigned; `err_place` is a place providing a reason why
/// `place` is not mutable (e.g., the non-`mut` local `x` in an
/// assignment to `x.f`).
pub(crate) fn report_illegal_reassignment(
&mut self,
(place, span): (Place<'tcx>, Span),
assigned_span: Span,
err_place: Place<'tcx>,
) {
let (from_arg, local_decl, local_name) = match err_place.as_local() {
Some(local) => (
self.body.local_kind(local) == LocalKind::Arg,
Some(&self.body.local_decls[local]),
self.local_names[local],
),
None => (false, None, None),
};
// If root local is initialized immediately (everything apart from let
// PATTERN;) then make the error refer to that local, rather than the
// place being assigned later.
let (place_description, assigned_span) = match local_decl {
Some(LocalDecl {
local_info:
ClearCrossCrate::Set(
box LocalInfo::User(BindingForm::Var(VarBindingForm {
opt_match_place: None,
..
}))
| box LocalInfo::StaticRef { .. }
| box LocalInfo::Boring,
),
..
})
| None => (self.describe_any_place(place.as_ref()), assigned_span),
Some(decl) => (self.describe_any_place(err_place.as_ref()), decl.source_info.span),
};
let mut err = self.cannot_reassign_immutable(span, &place_description, from_arg);
let msg = if from_arg {
"cannot assign to immutable argument"
} else {
"cannot assign twice to immutable variable"
};
if span != assigned_span && !from_arg {
err.span_label(assigned_span, format!("first assignment to {place_description}"));
}
if let Some(decl) = local_decl
&& let Some(name) = local_name
&& decl.can_be_made_mutable()
{
err.span_suggestion(
decl.source_info.span,
"consider making this binding mutable",
format!("mut {name}"),
Applicability::MachineApplicable,
);
if !from_arg
&& matches!(
decl.local_info(),
LocalInfo::User(BindingForm::Var(VarBindingForm {
opt_match_place: Some((Some(_), _)),
..
}))
)
{
err.span_suggestion(
decl.source_info.span,
"to modify the original value, take a borrow instead",
format!("ref mut {name}"),
Applicability::MaybeIncorrect,
);
}
}
err.span_label(span, msg);
self.buffer_error(err);
}
fn classify_drop_access_kind(&self, place: PlaceRef<'tcx>) -> StorageDeadOrDrop<'tcx> {
let tcx = self.infcx.tcx;
let (kind, _place_ty) = place.projection.iter().fold(
(LocalStorageDead, PlaceTy::from_ty(self.body.local_decls[place.local].ty)),
|(kind, place_ty), &elem| {
(
match elem {
ProjectionElem::Deref => match kind {
StorageDeadOrDrop::LocalStorageDead
| StorageDeadOrDrop::BoxedStorageDead => {
assert!(
place_ty.ty.is_box(),
"Drop of value behind a reference or raw pointer"
);
StorageDeadOrDrop::BoxedStorageDead
}
StorageDeadOrDrop::Destructor(_) => kind,
},
ProjectionElem::OpaqueCast { .. }
| ProjectionElem::Field(..)
| ProjectionElem::Downcast(..) => {
match place_ty.ty.kind() {
ty::Adt(def, _) if def.has_dtor(tcx) => {
// Report the outermost adt with a destructor
match kind {
StorageDeadOrDrop::Destructor(_) => kind,
StorageDeadOrDrop::LocalStorageDead
| StorageDeadOrDrop::BoxedStorageDead => {
StorageDeadOrDrop::Destructor(place_ty.ty)
}
}
}
_ => kind,
}
}
ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subslice { .. }
| ProjectionElem::Subtype(_)
| ProjectionElem::Index(_) => kind,
},
place_ty.projection_ty(tcx, elem),
)
},
);
kind
}
/// Describe the reason for the fake borrow that was assigned to `place`.
fn classify_immutable_section(&self, place: Place<'tcx>) -> Option<&'static str> {
use rustc_middle::mir::visit::Visitor;
struct FakeReadCauseFinder<'tcx> {
place: Place<'tcx>,
cause: Option<FakeReadCause>,
}
impl<'tcx> Visitor<'tcx> for FakeReadCauseFinder<'tcx> {
fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
match statement {
Statement { kind: StatementKind::FakeRead(box (cause, place)), .. }
if *place == self.place =>
{
self.cause = Some(*cause);
}
_ => (),
}
}
}
let mut visitor = FakeReadCauseFinder { place, cause: None };
visitor.visit_body(self.body);
match visitor.cause {
Some(FakeReadCause::ForMatchGuard) => Some("match guard"),
Some(FakeReadCause::ForIndex) => Some("indexing expression"),
_ => None,
}
}
/// Annotate argument and return type of function and closure with (synthesized) lifetime for
/// borrow of local value that does not live long enough.
fn annotate_argument_and_return_for_borrow(
&self,
borrow: &BorrowData<'tcx>,
) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
// Define a fallback for when we can't match a closure.
let fallback = || {
let is_closure = self.infcx.tcx.is_closure_like(self.mir_def_id().to_def_id());
if is_closure {
None
} else {
let ty = self.infcx.tcx.type_of(self.mir_def_id()).instantiate_identity();
match ty.kind() {
ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
self.mir_def_id(),
self.infcx.tcx.fn_sig(self.mir_def_id()).instantiate_identity(),
),
_ => None,
}
}
};
// In order to determine whether we need to annotate, we need to check whether the reserve
// place was an assignment into a temporary.
//
// If it was, we check whether or not that temporary is eventually assigned into the return
// place. If it was, we can add annotations about the function's return type and arguments
// and it'll make sense.
let location = borrow.reserve_location;
debug!("annotate_argument_and_return_for_borrow: location={:?}", location);
if let Some(Statement { kind: StatementKind::Assign(box (reservation, _)), .. }) =
&self.body[location.block].statements.get(location.statement_index)
{
debug!("annotate_argument_and_return_for_borrow: reservation={:?}", reservation);
// Check that the initial assignment of the reserve location is into a temporary.
let mut target = match reservation.as_local() {
Some(local) if self.body.local_kind(local) == LocalKind::Temp => local,
_ => return None,
};
// Next, look through the rest of the block, checking if we are assigning the
// `target` (that is, the place that contains our borrow) to anything.
let mut annotated_closure = None;
for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
debug!(
"annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
target, stmt
);
if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind {
if let Some(assigned_to) = place.as_local() {
debug!(
"annotate_argument_and_return_for_borrow: assigned_to={:?} \
rvalue={:?}",
assigned_to, rvalue
);
// Check if our `target` was captured by a closure.
if let Rvalue::Aggregate(
box AggregateKind::Closure(def_id, args),
operands,
) = rvalue
{
let def_id = def_id.expect_local();
for operand in operands {
let (Operand::Copy(assigned_from) | Operand::Move(assigned_from)) =
operand
else {
continue;
};
debug!(
"annotate_argument_and_return_for_borrow: assigned_from={:?}",
assigned_from
);
// Find the local from the operand.
let Some(assigned_from_local) =
assigned_from.local_or_deref_local()
else {
continue;
};
if assigned_from_local != target {
continue;
}
// If a closure captured our `target` and then assigned
// into a place then we should annotate the closure in
// case it ends up being assigned into the return place.
annotated_closure =
self.annotate_fn_sig(def_id, args.as_closure().sig());
debug!(
"annotate_argument_and_return_for_borrow: \
annotated_closure={:?} assigned_from_local={:?} \
assigned_to={:?}",
annotated_closure, assigned_from_local, assigned_to
);
if assigned_to == mir::RETURN_PLACE {
// If it was assigned directly into the return place, then
// return now.
return annotated_closure;
} else {
// Otherwise, update the target.
target = assigned_to;
}
}
// If none of our closure's operands matched, then skip to the next
// statement.
continue;
}
// Otherwise, look at other types of assignment.
let assigned_from = match rvalue {
Rvalue::Ref(_, _, assigned_from) => assigned_from,
Rvalue::Use(operand) => match operand {
Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
assigned_from
}
_ => continue,
},
_ => continue,
};
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from={:?}",
assigned_from,
);
// Find the local from the rvalue.
let Some(assigned_from_local) = assigned_from.local_or_deref_local() else {
continue;
};
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from_local={:?}",
assigned_from_local,
);
// Check if our local matches the target - if so, we've assigned our
// borrow to a new place.
if assigned_from_local != target {
continue;
}
// If we assigned our `target` into a new place, then we should
// check if it was the return place.
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from_local={:?} assigned_to={:?}",
assigned_from_local, assigned_to
);
if assigned_to == mir::RETURN_PLACE {
// If it was then return the annotated closure if there was one,
// else, annotate this function.
return annotated_closure.or_else(fallback);
}
// If we didn't assign into the return place, then we just update
// the target.
target = assigned_to;
}
}
}
// Check the terminator if we didn't find anything in the statements.
let terminator = &self.body[location.block].terminator();
debug!(
"annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
target, terminator
);
if let TerminatorKind::Call { destination, target: Some(_), args, .. } =
&terminator.kind
{
if let Some(assigned_to) = destination.as_local() {
debug!(
"annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
assigned_to, args
);
for operand in args {
let (Operand::Copy(assigned_from) | Operand::Move(assigned_from)) =
&operand.node
else {
continue;
};
debug!(
"annotate_argument_and_return_for_borrow: assigned_from={:?}",
assigned_from,
);
if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
debug!(
"annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
assigned_from_local,
);
if assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
return annotated_closure.or_else(fallback);
}
}
}
}
}
}
// If we haven't found an assignment into the return place, then we need not add
// any annotations.
debug!("annotate_argument_and_return_for_borrow: none found");
None
}
/// Annotate the first argument and return type of a function signature if they are
/// references.
fn annotate_fn_sig(
&self,
did: LocalDefId,
sig: ty::PolyFnSig<'tcx>,
) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
let is_closure = self.infcx.tcx.is_closure_like(did.to_def_id());
let fn_hir_id = self.infcx.tcx.local_def_id_to_hir_id(did);
let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
// We need to work out which arguments to highlight. We do this by looking
// at the return type, where there are three cases:
//
// 1. If there are named arguments, then we should highlight the return type and
// highlight any of the arguments that are also references with that lifetime.
// If there are no arguments that have the same lifetime as the return type,
// then don't highlight anything.
// 2. The return type is a reference with an anonymous lifetime. If this is
// the case, then we can take advantage of (and teach) the lifetime elision
// rules.
//
// We know that an error is being reported. So the arguments and return type
// must satisfy the elision rules. Therefore, if there is a single argument
// then that means the return type and first (and only) argument have the same
// lifetime and the borrow isn't meeting that, we can highlight the argument
// and return type.
//
// If there are multiple arguments then the first argument must be self (else
// it would not satisfy the elision rules), so we can highlight self and the
// return type.
// 3. The return type is not a reference. In this case, we don't highlight
// anything.
let return_ty = sig.output();
match return_ty.skip_binder().kind() {
ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
// This is case 1 from above, return type is a named reference so we need to
// search for relevant arguments.
let mut arguments = Vec::new();
for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
if let ty::Ref(argument_region, _, _) = argument.kind() {
if argument_region == return_region {
// Need to use the `rustc_middle::ty` types to compare against the
// `return_region`. Then use the `rustc_hir` type to get only
// the lifetime span.
if let hir::TyKind::Ref(lifetime, _) = &fn_decl.inputs[index].kind {
// With access to the lifetime, we can get
// the span of it.
arguments.push((*argument, lifetime.ident.span));
} else {
bug!("ty type is a ref but hir type is not");
}
}
}
}
// We need to have arguments. This shouldn't happen, but it's worth checking.
if arguments.is_empty() {
return None;
}
// We use a mix of the HIR and the Ty types to get information
// as the HIR doesn't have full types for closure arguments.
let return_ty = sig.output().skip_binder();
let mut return_span = fn_decl.output.span();
if let hir::FnRetTy::Return(ty) = &fn_decl.output {
if let hir::TyKind::Ref(lifetime, _) = ty.kind {
return_span = lifetime.ident.span;
}
}
Some(AnnotatedBorrowFnSignature::NamedFunction {
arguments,
return_ty,
return_span,
})
}
ty::Ref(_, _, _) if is_closure => {
// This is case 2 from above but only for closures, return type is anonymous
// reference so we select
// the first argument.
let argument_span = fn_decl.inputs.first()?.span;
let argument_ty = sig.inputs().skip_binder().first()?;
// Closure arguments are wrapped in a tuple, so we need to get the first
// from that.
if let ty::Tuple(elems) = argument_ty.kind() {
let &argument_ty = elems.first()?;
if let ty::Ref(_, _, _) = argument_ty.kind() {
return Some(AnnotatedBorrowFnSignature::Closure {
argument_ty,
argument_span,
});
}
}
None
}
ty::Ref(_, _, _) => {
// This is also case 2 from above but for functions, return type is still an
// anonymous reference so we select the first argument.
let argument_span = fn_decl.inputs.first()?.span;
let argument_ty = *sig.inputs().skip_binder().first()?;
let return_span = fn_decl.output.span();
let return_ty = sig.output().skip_binder();
// We expect the first argument to be a reference.
match argument_ty.kind() {
ty::Ref(_, _, _) => {}
_ => return None,
}
Some(AnnotatedBorrowFnSignature::AnonymousFunction {
argument_ty,
argument_span,
return_ty,
return_span,
})
}
_ => {
// This is case 3 from above, return type is not a reference so don't highlight
// anything.
None
}
}
}
}
#[derive(Debug)]
enum AnnotatedBorrowFnSignature<'tcx> {
NamedFunction {
arguments: Vec<(Ty<'tcx>, Span)>,
return_ty: Ty<'tcx>,
return_span: Span,
},
AnonymousFunction {
argument_ty: Ty<'tcx>,
argument_span: Span,
return_ty: Ty<'tcx>,
return_span: Span,
},
Closure {
argument_ty: Ty<'tcx>,
argument_span: Span,
},
}
impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
/// Annotate the provided diagnostic with information about borrow from the fn signature that
/// helps explain.
pub(crate) fn emit(&self, cx: &MirBorrowckCtxt<'_, 'tcx>, diag: &mut Diag<'_>) -> String {
match self {
&AnnotatedBorrowFnSignature::Closure { argument_ty, argument_span } => {
diag.span_label(
argument_span,
format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
);
cx.get_region_name_for_ty(argument_ty, 0)
}
&AnnotatedBorrowFnSignature::AnonymousFunction {
argument_ty,
argument_span,
return_ty,
return_span,
} => {
let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
diag.span_label(argument_span, format!("has type `{argument_ty_name}`"));
let return_ty_name = cx.get_name_for_ty(return_ty, 0);
let types_equal = return_ty_name == argument_ty_name;
diag.span_label(
return_span,
format!(
"{}has type `{}`",
if types_equal { "also " } else { "" },
return_ty_name,
),
);
diag.note(
"argument and return type have the same lifetime due to lifetime elision rules",
);
diag.note(
"to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
lifetime-syntax.html#lifetime-elision>",
);
cx.get_region_name_for_ty(return_ty, 0)
}
AnnotatedBorrowFnSignature::NamedFunction { arguments, return_ty, return_span } => {
// Region of return type and arguments checked to be the same earlier.
let region_name = cx.get_region_name_for_ty(*return_ty, 0);
for (_, argument_span) in arguments {
diag.span_label(*argument_span, format!("has lifetime `{region_name}`"));
}
diag.span_label(*return_span, format!("also has lifetime `{region_name}`",));
diag.help(format!(
"use data from the highlighted arguments which match the `{region_name}` lifetime of \
the return type",
));
region_name
}
}
}
}
/// Detect whether one of the provided spans is a statement nested within the top-most visited expr
struct ReferencedStatementsVisitor<'a>(&'a [Span], bool);
impl<'a, 'v> Visitor<'v> for ReferencedStatementsVisitor<'a> {
fn visit_stmt(&mut self, s: &'v hir::Stmt<'v>) {
match s.kind {
hir::StmtKind::Semi(expr) if self.0.contains(&expr.span) => {
self.1 = true;
}
_ => {}
}
}
}
/// Look for `break` expressions within any arbitrary expressions. We'll do this to infer
/// whether this is a case where the moved value would affect the exit of a loop, making it
/// unsuitable for a `.clone()` suggestion.
struct BreakFinder {
found_breaks: Vec<(hir::Destination, Span)>,
found_continues: Vec<(hir::Destination, Span)>,
}
impl<'hir> Visitor<'hir> for BreakFinder {
fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
match ex.kind {
hir::ExprKind::Break(destination, _) => {
self.found_breaks.push((destination, ex.span));
}
hir::ExprKind::Continue(destination) => {
self.found_continues.push((destination, ex.span));
}
_ => {}
}
hir::intravisit::walk_expr(self, ex);
}
}
/// Given a set of spans representing statements initializing the relevant binding, visit all the
/// function expressions looking for branching code paths that *do not* initialize the binding.
struct ConditionVisitor<'b> {
spans: &'b [Span],
name: &'b str,
errors: Vec<(Span, String)>,
}
impl<'b, 'v> Visitor<'v> for ConditionVisitor<'b> {
fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
match ex.kind {
hir::ExprKind::If(cond, body, None) => {
// `if` expressions with no `else` that initialize the binding might be missing an
// `else` arm.
let mut v = ReferencedStatementsVisitor(self.spans, false);
v.visit_expr(body);
if v.1 {
self.errors.push((
cond.span,
format!(
"if this `if` condition is `false`, {} is not initialized",
self.name,
),
));
self.errors.push((
ex.span.shrink_to_hi(),
format!("an `else` arm might be missing here, initializing {}", self.name),
));
}
}
hir::ExprKind::If(cond, body, Some(other)) => {
// `if` expressions where the binding is only initialized in one of the two arms
// might be missing a binding initialization.
let mut a = ReferencedStatementsVisitor(self.spans, false);
a.visit_expr(body);
let mut b = ReferencedStatementsVisitor(self.spans, false);
b.visit_expr(other);
match (a.1, b.1) {
(true, true) | (false, false) => {}
(true, false) => {
if other.span.is_desugaring(DesugaringKind::WhileLoop) {
self.errors.push((
cond.span,
format!(
"if this condition isn't met and the `while` loop runs 0 \
times, {} is not initialized",
self.name
),
));
} else {
self.errors.push((
body.span.shrink_to_hi().until(other.span),
format!(
"if the `if` condition is `false` and this `else` arm is \
executed, {} is not initialized",
self.name
),
));
}
}
(false, true) => {
self.errors.push((
cond.span,
format!(
"if this condition is `true`, {} is not initialized",
self.name
),
));
}
}
}
hir::ExprKind::Match(e, arms, loop_desugar) => {
// If the binding is initialized in one of the match arms, then the other match
// arms might be missing an initialization.
let results: Vec<bool> = arms
.iter()
.map(|arm| {
let mut v = ReferencedStatementsVisitor(self.spans, false);
v.visit_arm(arm);
v.1
})
.collect();
if results.iter().any(|x| *x) && !results.iter().all(|x| *x) {
for (arm, seen) in arms.iter().zip(results) {
if !seen {
if loop_desugar == hir::MatchSource::ForLoopDesugar {
self.errors.push((
e.span,
format!(
"if the `for` loop runs 0 times, {} is not initialized",
self.name
),
));
} else if let Some(guard) = &arm.guard {
self.errors.push((
arm.pat.span.to(guard.span),
format!(
"if this pattern and condition are matched, {} is not \
initialized",
self.name
),
));
} else {
self.errors.push((
arm.pat.span,
format!(
"if this pattern is matched, {} is not initialized",
self.name
),
));
}
}
}
}
}
// FIXME: should we also account for binops, particularly `&&` and `||`? `try` should
// also be accounted for. For now it is fine, as if we don't find *any* relevant
// branching code paths, we point at the places where the binding *is* initialized for
// *some* context.
_ => {}
}
walk_expr(self, ex);
}
}