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fuchsia / third_party / rust / c38f75c21f016bffbf841ed5abce338f94201bde / . / compiler / rustc_hir_typeck / src / pat.rs
blob: 8c7ae7f8e980da279e1b73228afb6dc66ac780a2 [file] [log] [blame]
use crate::gather_locals::DeclOrigin;
use crate::{errors, FnCtxt, LoweredTy};
use rustc_ast as ast;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{
codes::*, pluralize, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, MultiSpan,
};
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::pat_util::EnumerateAndAdjustIterator;
use rustc_hir::{self as hir, BindingMode, ByRef, HirId, Mutability, Pat, PatKind};
use rustc_infer::infer;
use rustc_infer::infer::type_variable::TypeVariableOrigin;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::ty::{self, Ty, TypeVisitableExt};
use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
use rustc_span::edit_distance::find_best_match_for_name;
use rustc_span::hygiene::DesugaringKind;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident};
use rustc_span::{BytePos, Span, DUMMY_SP};
use rustc_target::abi::FieldIdx;
use rustc_trait_selection::traits::{ObligationCause, Pattern};
use ty::VariantDef;
use std::cmp;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use super::report_unexpected_variant_res;
const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
this type has no compile-time size. Therefore, all accesses to trait types must be through \
pointers. If you encounter this error you should try to avoid dereferencing the pointer.
You can read more about trait objects in the Trait Objects section of the Reference: \
https://doc.rust-lang.org/reference/types.html#trait-objects";
fn is_number(text: &str) -> bool {
text.chars().all(|c: char| c.is_digit(10))
}
/// Information about the expected type at the top level of type checking a pattern.
///
/// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
#[derive(Copy, Clone)]
struct TopInfo<'tcx> {
/// The `expected` type at the top level of type checking a pattern.
expected: Ty<'tcx>,
/// Was the origin of the `span` from a scrutinee expression?
///
/// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
origin_expr: Option<&'tcx hir::Expr<'tcx>>,
/// The span giving rise to the `expected` type, if one could be provided.
///
/// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
///
/// - `match scrutinee { ... }`
/// - `let _ = scrutinee;`
///
/// This is used to point to add context in type errors.
/// In the following example, `span` corresponds to the `a + b` expression:
///
/// ```text
/// error[E0308]: mismatched types
/// --> src/main.rs:L:C
/// |
/// L | let temp: usize = match a + b {
/// | ----- this expression has type `usize`
/// L | Ok(num) => num,
/// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
/// |
/// = note: expected type `usize`
/// found type `std::result::Result<_, _>`
/// ```
span: Option<Span>,
}
#[derive(Copy, Clone)]
struct PatInfo<'tcx, 'a> {
binding_mode: ByRef,
max_ref_mutbl: Mutability,
top_info: TopInfo<'tcx>,
decl_origin: Option<DeclOrigin<'a>>,
/// The depth of current pattern
current_depth: u32,
}
impl<'tcx> FnCtxt<'_, 'tcx> {
fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
let code =
Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr.is_some() };
self.cause(cause_span, code)
}
fn demand_eqtype_pat_diag(
&self,
cause_span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Option<Diag<'tcx>> {
let mut diag =
self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)?;
if let Some(expr) = ti.origin_expr {
self.suggest_fn_call(&mut diag, expr, expected, |output| {
self.can_eq(self.param_env, output, actual)
});
}
Some(diag)
}
fn demand_eqtype_pat(
&self,
cause_span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
ti: TopInfo<'tcx>,
) {
if let Some(err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
err.emit();
}
}
}
/// Mode for adjusting the expected type and binding mode.
enum AdjustMode {
/// Peel off all immediate reference types.
Peel,
/// Reset binding mode to the initial mode.
/// Used for destructuring assignment, where we don't want any match ergonomics.
Reset,
/// Produced by ref patterns.
/// Reset the binding mode to the initial mode,
/// and if the old biding mode was by-reference
/// with mutability matching the pattern,
/// mark the pattern as having consumed this reference.
ResetAndConsumeRef(Mutability),
/// Pass on the input binding mode and expected type.
Pass,
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Type check the given top level pattern against the `expected` type.
///
/// If a `Some(span)` is provided and `origin_expr` holds,
/// then the `span` represents the scrutinee's span.
/// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
///
/// Otherwise, `Some(span)` represents the span of a type expression
/// which originated the `expected` type.
pub(crate) fn check_pat_top(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
span: Option<Span>,
origin_expr: Option<&'tcx hir::Expr<'tcx>>,
decl_origin: Option<DeclOrigin<'tcx>>,
) {
let info = TopInfo { expected, origin_expr, span };
let pat_info = PatInfo {
binding_mode: ByRef::No,
max_ref_mutbl: Mutability::Mut,
top_info: info,
decl_origin,
current_depth: 0,
};
self.check_pat(pat, expected, pat_info);
}
/// Type check the given `pat` against the `expected` type
/// with the provided `def_bm` (default binding mode).
///
/// Outside of this module, `check_pat_top` should always be used.
/// Conversely, inside this module, `check_pat_top` should never be used.
#[instrument(level = "debug", skip(self, pat_info))]
fn check_pat(&self, pat: &'tcx Pat<'tcx>, expected: Ty<'tcx>, pat_info: PatInfo<'tcx, '_>) {
let PatInfo { binding_mode: def_bm, max_ref_mutbl, top_info: ti, current_depth, .. } =
pat_info;
let path_res = match &pat.kind {
PatKind::Path(qpath) => Some(
self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span, None),
),
_ => None,
};
let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
let (expected, def_bm, max_ref_mutbl, ref_pattern_already_consumed) =
self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode, max_ref_mutbl);
let pat_info = PatInfo {
binding_mode: def_bm,
max_ref_mutbl,
top_info: ti,
decl_origin: pat_info.decl_origin,
current_depth: current_depth + 1,
};
let ty = match pat.kind {
PatKind::Wild | PatKind::Err(_) => expected,
// We allow any type here; we ensure that the type is uninhabited during match checking.
PatKind::Never => expected,
PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
PatKind::Binding(ba, var_id, _, sub) => {
self.check_pat_ident(pat, ba, var_id, sub, expected, pat_info)
}
PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, pat_info)
}
PatKind::Path(ref qpath) => {
self.check_pat_path(pat, qpath, path_res.unwrap(), expected, ti)
}
PatKind::Struct(ref qpath, fields, has_rest_pat) => {
self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, pat_info)
}
PatKind::Or(pats) => {
for pat in pats {
self.check_pat(pat, expected, pat_info);
}
expected
}
PatKind::Tuple(elements, ddpos) => {
self.check_pat_tuple(pat.span, elements, ddpos, expected, pat_info)
}
PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, pat_info),
PatKind::Deref(inner) => self.check_pat_deref(pat.span, inner, expected, pat_info),
PatKind::Ref(inner, mutbl) => self.check_pat_ref(
pat,
inner,
mutbl,
expected,
pat_info,
ref_pattern_already_consumed,
),
PatKind::Slice(before, slice, after) => {
self.check_pat_slice(pat.span, before, slice, after, expected, pat_info)
}
};
self.write_ty(pat.hir_id, ty);
// (note_1): In most of the cases where (note_1) is referenced
// (literals and constants being the exception), we relate types
// using strict equality, even though subtyping would be sufficient.
// There are a few reasons for this, some of which are fairly subtle
// and which cost me (nmatsakis) an hour or two debugging to remember,
// so I thought I'd write them down this time.
//
// 1. There is no loss of expressiveness here, though it does
// cause some inconvenience. What we are saying is that the type
// of `x` becomes *exactly* what is expected. This can cause unnecessary
// errors in some cases, such as this one:
//
// ```
// fn foo<'x>(x: &'x i32) {
// let a = 1;
// let mut z = x;
// z = &a;
// }
// ```
//
// The reason we might get an error is that `z` might be
// assigned a type like `&'x i32`, and then we would have
// a problem when we try to assign `&a` to `z`, because
// the lifetime of `&a` (i.e., the enclosing block) is
// shorter than `'x`.
//
// HOWEVER, this code works fine. The reason is that the
// expected type here is whatever type the user wrote, not
// the initializer's type. In this case the user wrote
// nothing, so we are going to create a type variable `Z`.
// Then we will assign the type of the initializer (`&'x i32`)
// as a subtype of `Z`: `&'x i32 <: Z`. And hence we
// will instantiate `Z` as a type `&'0 i32` where `'0` is
// a fresh region variable, with the constraint that `'x : '0`.
// So basically we're all set.
//
// Note that there are two tests to check that this remains true
// (`regions-reassign-{match,let}-bound-pointer.rs`).
//
// 2. An outdated issue related to the old HIR borrowck. See the test
// `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
}
/// Compute the new expected type and default binding mode from the old ones
/// as well as the pattern form we are currently checking.
///
/// Last entry is only relevant for ref patterns (`&` and `&mut`);
/// if `true`, then the ref pattern consumed a match ergonomics inserted reference
/// and so does no need to match against a reference in the scrutinee type.
fn calc_default_binding_mode(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
def_br: ByRef,
adjust_mode: AdjustMode,
max_ref_mutbl: Mutability,
) -> (Ty<'tcx>, ByRef, Mutability, bool) {
if let ByRef::Yes(mutbl) = def_br {
debug_assert!(mutbl <= max_ref_mutbl);
}
match adjust_mode {
AdjustMode::Pass => (expected, def_br, max_ref_mutbl, false),
AdjustMode::Reset => (expected, ByRef::No, Mutability::Mut, false),
AdjustMode::ResetAndConsumeRef(ref_pat_mutbl) => {
let mutbls_match = def_br == ByRef::Yes(ref_pat_mutbl);
if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 {
if mutbls_match {
debug!("consuming inherited reference");
(expected, ByRef::No, cmp::min(max_ref_mutbl, ref_pat_mutbl), true)
} else {
let (new_ty, new_bm, max_ref_mutbl) = if ref_pat_mutbl == Mutability::Mut {
self.peel_off_references(
pat,
expected,
def_br,
Mutability::Not,
max_ref_mutbl,
)
} else {
(expected, def_br.cap_ref_mutability(Mutability::Not), Mutability::Not)
};
(new_ty, new_bm, max_ref_mutbl, false)
}
} else {
(expected, ByRef::No, max_ref_mutbl, mutbls_match)
}
}
AdjustMode::Peel => {
let peeled =
self.peel_off_references(pat, expected, def_br, Mutability::Mut, max_ref_mutbl);
(peeled.0, peeled.1, peeled.2, false)
}
}
}
/// How should the binding mode and expected type be adjusted?
///
/// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
// When we perform destructuring assignment, we disable default match bindings, which are
// unintuitive in this context.
if !pat.default_binding_modes {
return AdjustMode::Reset;
}
match &pat.kind {
// Type checking these product-like types successfully always require
// that the expected type be of those types and not reference types.
PatKind::Struct(..)
| PatKind::TupleStruct(..)
| PatKind::Tuple(..)
| PatKind::Box(_)
| PatKind::Deref(_)
| PatKind::Range(..)
| PatKind::Slice(..) => AdjustMode::Peel,
// A never pattern behaves somewhat like a literal or unit variant.
PatKind::Never => AdjustMode::Peel,
// String and byte-string literals result in types `&str` and `&[u8]` respectively.
// All other literals result in non-reference types.
// As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo" {}`.
//
// Call `resolve_vars_if_possible` here for inline const blocks.
PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
ty::Ref(..) => AdjustMode::Pass,
_ => AdjustMode::Peel,
},
PatKind::Path(_) => match opt_path_res.unwrap() {
// These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
// Peeling the reference types too early will cause type checking failures.
// Although it would be possible to *also* peel the types of the constants too.
Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
// In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
// could successfully compile. The former being `Self` requires a unit struct.
// In either case, and unlike constants, the pattern itself cannot be
// a reference type wherefore peeling doesn't give up any expressiveness.
_ => AdjustMode::Peel,
},
// When encountering a `& mut? pat` pattern, reset to "by value".
// This is so that `x` and `y` here are by value, as they appear to be:
//
// ```
// match &(&22, &44) {
// (&x, &y) => ...
// }
// ```
//
// See issue #46688.
PatKind::Ref(_, mutbl) => AdjustMode::ResetAndConsumeRef(*mutbl),
// A `_` pattern works with any expected type, so there's no need to do anything.
PatKind::Wild
// A malformed pattern doesn't have an expected type, so let's just accept any type.
| PatKind::Err(_)
// Bindings also work with whatever the expected type is,
// and moreover if we peel references off, that will give us the wrong binding type.
// Also, we can have a subpattern `binding @ pat`.
// Each side of the `@` should be treated independently (like with OR-patterns).
| PatKind::Binding(..)
// An OR-pattern just propagates to each individual alternative.
// This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
// In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
| PatKind::Or(_) => AdjustMode::Pass,
}
}
/// Peel off as many immediately nested `& mut?` from the expected type as possible
/// and return the new expected type and binding default binding mode.
/// The adjustments vector, if non-empty is stored in a table.
fn peel_off_references(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
mut def_br: ByRef,
max_peelable_mutability: Mutability,
mut max_ref_mutability: Mutability,
) -> (Ty<'tcx>, ByRef, Mutability) {
let mut expected = self.try_structurally_resolve_type(pat.span, expected);
// Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
// for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
// the `Some(5)` which is not of type Ref.
//
// For each ampersand peeled off, update the binding mode and push the original
// type into the adjustments vector.
//
// See the examples in `ui/match-defbm*.rs`.
let mut pat_adjustments = vec![];
while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind()
&& inner_mutability <= max_peelable_mutability
{
debug!("inspecting {:?}", expected);
debug!("current discriminant is Ref, inserting implicit deref");
// Preserve the reference type. We'll need it later during THIR lowering.
pat_adjustments.push(expected);
expected = self.try_structurally_resolve_type(pat.span, inner_ty);
def_br = ByRef::Yes(match def_br {
// If default binding mode is by value, make it `ref` or `ref mut`
// (depending on whether we observe `&` or `&mut`).
ByRef::No |
// When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
ByRef::Yes(Mutability::Mut) => inner_mutability,
// Once a `ref`, always a `ref`.
// This is because a `& &mut` cannot mutate the underlying value.
ByRef::Yes(Mutability::Not) => Mutability::Not,
});
}
if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 {
def_br = def_br.cap_ref_mutability(max_ref_mutability);
if def_br == ByRef::Yes(Mutability::Not) {
max_ref_mutability = Mutability::Not;
}
}
if !pat_adjustments.is_empty() {
debug!("default binding mode is now {:?}", def_br);
self.typeck_results
.borrow_mut()
.pat_adjustments_mut()
.insert(pat.hir_id, pat_adjustments);
}
(expected, def_br, max_ref_mutability)
}
fn check_pat_lit(
&self,
span: Span,
lt: &hir::Expr<'tcx>,
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
// We've already computed the type above (when checking for a non-ref pat),
// so avoid computing it again.
let ty = self.node_ty(lt.hir_id);
// Byte string patterns behave the same way as array patterns
// They can denote both statically and dynamically-sized byte arrays.
let mut pat_ty = ty;
if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(..), .. }) = lt.kind {
let expected = self.structurally_resolve_type(span, expected);
if let ty::Ref(_, inner_ty, _) = *expected.kind()
&& self.try_structurally_resolve_type(span, inner_ty).is_slice()
{
let tcx = self.tcx;
trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
self.typeck_results
.borrow_mut()
.treat_byte_string_as_slice
.insert(lt.hir_id.local_id);
pat_ty =
Ty::new_imm_ref(tcx, tcx.lifetimes.re_static, Ty::new_slice(tcx, tcx.types.u8));
}
}
if self.tcx.features().string_deref_patterns
&& let hir::ExprKind::Lit(Spanned { node: ast::LitKind::Str(..), .. }) = lt.kind
{
let tcx = self.tcx;
let expected = self.resolve_vars_if_possible(expected);
pat_ty = match expected.kind() {
ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => expected,
ty::Str => Ty::new_static_str(tcx),
_ => pat_ty,
};
}
// Somewhat surprising: in this case, the subtyping relation goes the
// opposite way as the other cases. Actually what we really want is not
// a subtyping relation at all but rather that there exists a LUB
// (so that they can be compared). However, in practice, constants are
// always scalars or strings. For scalars subtyping is irrelevant,
// and for strings `ty` is type is `&'static str`, so if we say that
//
// &'static str <: expected
//
// then that's equivalent to there existing a LUB.
let cause = self.pattern_cause(ti, span);
if let Some(err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
err.emit_unless(
ti.span
.filter(|&s| {
// In the case of `if`- and `while`-expressions we've already checked
// that `scrutinee: bool`. We know that the pattern is `true`,
// so an error here would be a duplicate and from the wrong POV.
s.is_desugaring(DesugaringKind::CondTemporary)
})
.is_some(),
);
}
pat_ty
}
fn check_pat_range(
&self,
span: Span,
lhs: Option<&'tcx hir::Expr<'tcx>>,
rhs: Option<&'tcx hir::Expr<'tcx>>,
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
None => None,
Some(expr) => {
let ty = self.check_expr(expr);
// Check that the end-point is possibly of numeric or char type.
// The early check here is not for correctness, but rather better
// diagnostics (e.g. when `&str` is being matched, `expected` will
// be peeled to `str` while ty here is still `&str`, if we don't
// err early here, a rather confusing unification error will be
// emitted instead).
let fail =
!(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
Some((fail, ty, expr.span))
}
};
let mut lhs = calc_side(lhs);
let mut rhs = calc_side(rhs);
if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
// There exists a side that didn't meet our criteria that the end-point
// be of a numeric or char type, as checked in `calc_side` above.
let guar = self.emit_err_pat_range(span, lhs, rhs);
return Ty::new_error(self.tcx, guar);
}
// Unify each side with `expected`.
// Subtyping doesn't matter here, as the value is some kind of scalar.
let demand_eqtype = |x: &mut _, y| {
if let Some((ref mut fail, x_ty, x_span)) = *x
&& let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
{
if let Some((_, y_ty, y_span)) = y {
self.endpoint_has_type(&mut err, y_span, y_ty);
}
err.emit();
*fail = true;
}
};
demand_eqtype(&mut lhs, rhs);
demand_eqtype(&mut rhs, lhs);
if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
return Ty::new_misc_error(self.tcx);
}
// Find the unified type and check if it's of numeric or char type again.
// This check is needed if both sides are inference variables.
// We require types to be resolved here so that we emit inference failure
// rather than "_ is not a char or numeric".
let ty = self.structurally_resolve_type(span, expected);
if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
if let Some((ref mut fail, _, _)) = lhs {
*fail = true;
}
if let Some((ref mut fail, _, _)) = rhs {
*fail = true;
}
let guar = self.emit_err_pat_range(span, lhs, rhs);
return Ty::new_error(self.tcx, guar);
}
ty
}
fn endpoint_has_type(&self, err: &mut Diag<'_>, span: Span, ty: Ty<'_>) {
if !ty.references_error() {
err.span_label(span, format!("this is of type `{ty}`"));
}
}
fn emit_err_pat_range(
&self,
span: Span,
lhs: Option<(bool, Ty<'tcx>, Span)>,
rhs: Option<(bool, Ty<'tcx>, Span)>,
) -> ErrorGuaranteed {
let span = match (lhs, rhs) {
(Some((true, ..)), Some((true, ..))) => span,
(Some((true, _, sp)), _) => sp,
(_, Some((true, _, sp))) => sp,
_ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
};
let mut err = struct_span_code_err!(
self.dcx(),
span,
E0029,
"only `char` and numeric types are allowed in range patterns"
);
let msg = |ty| {
let ty = self.resolve_vars_if_possible(ty);
format!("this is of type `{ty}` but it should be `char` or numeric")
};
let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
err.span_label(first_span, msg(first_ty));
if let Some((_, ty, sp)) = second {
let ty = self.resolve_vars_if_possible(ty);
self.endpoint_has_type(&mut err, sp, ty);
}
};
match (lhs, rhs) {
(Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
err.span_label(lhs_sp, msg(lhs_ty));
err.span_label(rhs_sp, msg(rhs_ty));
}
(Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
(lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
_ => span_bug!(span, "Impossible, verified above."),
}
if (lhs, rhs).references_error() {
err.downgrade_to_delayed_bug();
}
if self.tcx.sess.teach(err.code.unwrap()) {
err.note(
"In a match expression, only numbers and characters can be matched \
against a range. This is because the compiler checks that the range \
is non-empty at compile-time, and is unable to evaluate arbitrary \
comparison functions. If you want to capture values of an orderable \
type between two end-points, you can use a guard.",
);
}
err.emit()
}
fn check_pat_ident(
&self,
pat: &'tcx Pat<'tcx>,
ba: BindingMode,
var_id: HirId,
sub: Option<&'tcx Pat<'tcx>>,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let PatInfo { binding_mode: def_br, top_info: ti, .. } = pat_info;
// Determine the binding mode...
let bm = match ba {
BindingMode(ByRef::No, Mutability::Mut)
if !(pat.span.at_least_rust_2024()
&& self.tcx.features().mut_preserve_binding_mode_2024)
&& matches!(def_br, ByRef::Yes(_)) =>
{
// `mut x` resets the binding mode in edition <= 2021.
self.tcx.emit_node_span_lint(
rustc_lint::builtin::DEREFERENCING_MUT_BINDING,
pat.hir_id,
pat.span,
errors::DereferencingMutBinding { span: pat.span },
);
BindingMode(ByRef::No, Mutability::Mut)
}
BindingMode(ByRef::No, mutbl) => BindingMode(def_br, mutbl),
BindingMode(ByRef::Yes(_), _) => ba,
};
// ...and store it in a side table:
self.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
let local_ty = self.local_ty(pat.span, pat.hir_id);
let eq_ty = match bm.0 {
ByRef::Yes(mutbl) => {
// If the binding is like `ref x | ref mut x`,
// then `x` is assigned a value of type `&M T` where M is the
// mutability and T is the expected type.
//
// `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
// is required. However, we use equality, which is stronger.
// See (note_1) for an explanation.
self.new_ref_ty(pat.span, mutbl, expected)
}
// Otherwise, the type of x is the expected type `T`.
ByRef::No => expected, // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
};
self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
// If there are multiple arms, make sure they all agree on
// what the type of the binding `x` ought to be.
if var_id != pat.hir_id {
self.check_binding_alt_eq_ty(ba, pat.span, var_id, local_ty, ti);
}
if let Some(p) = sub {
self.check_pat(p, expected, pat_info);
}
local_ty
}
/// When a variable is bound several times in a `PatKind::Or`, it'll resolve all of the
/// subsequent bindings of the same name to the first usage. Verify that all of these
/// bindings have the same type by comparing them all against the type of that first pat.
fn check_binding_alt_eq_ty(
&self,
ba: BindingMode,
span: Span,
var_id: HirId,
ty: Ty<'tcx>,
ti: TopInfo<'tcx>,
) {
let var_ty = self.local_ty(span, var_id);
if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
let hir = self.tcx.hir();
let var_ty = self.resolve_vars_if_possible(var_ty);
let msg = format!("first introduced with type `{var_ty}` here");
err.span_label(hir.span(var_id), msg);
let in_match = hir.parent_iter(var_id).any(|(_, n)| {
matches!(
n,
hir::Node::Expr(hir::Expr {
kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
..
})
)
});
let pre = if in_match { "in the same arm, " } else { "" };
err.note(format!("{pre}a binding must have the same type in all alternatives"));
self.suggest_adding_missing_ref_or_removing_ref(
&mut err,
span,
var_ty,
self.resolve_vars_if_possible(ty),
ba,
);
err.emit();
}
}
fn suggest_adding_missing_ref_or_removing_ref(
&self,
err: &mut Diag<'_>,
span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
ba: BindingMode,
) {
match (expected.kind(), actual.kind(), ba) {
(ty::Ref(_, inner_ty, _), _, BindingMode::NONE)
if self.can_eq(self.param_env, *inner_ty, actual) =>
{
err.span_suggestion_verbose(
span.shrink_to_lo(),
"consider adding `ref`",
"ref ",
Applicability::MaybeIncorrect,
);
}
(_, ty::Ref(_, inner_ty, _), BindingMode::REF)
if self.can_eq(self.param_env, expected, *inner_ty) =>
{
err.span_suggestion_verbose(
span.with_hi(span.lo() + BytePos(4)),
"consider removing `ref`",
"",
Applicability::MaybeIncorrect,
);
}
_ => (),
}
}
/// Precondition: pat is a `Ref(_)` pattern
fn borrow_pat_suggestion(&self, err: &mut Diag<'_>, pat: &Pat<'_>) {
let tcx = self.tcx;
if let PatKind::Ref(inner, mutbl) = pat.kind
&& let PatKind::Binding(_, _, binding, ..) = inner.kind
{
let binding_parent = tcx.parent_hir_node(pat.hir_id);
debug!(?inner, ?pat, ?binding_parent);
let mutability = match mutbl {
ast::Mutability::Mut => "mut",
ast::Mutability::Not => "",
};
let mut_var_suggestion = 'block: {
if mutbl.is_not() {
break 'block None;
}
let ident_kind = match binding_parent {
hir::Node::Param(_) => "parameter",
hir::Node::LetStmt(_) => "variable",
hir::Node::Arm(_) => "binding",
// Provide diagnostics only if the parent pattern is struct-like,
// i.e. where `mut binding` makes sense
hir::Node::Pat(Pat { kind, .. }) => match kind {
PatKind::Struct(..)
| PatKind::TupleStruct(..)
| PatKind::Or(..)
| PatKind::Tuple(..)
| PatKind::Slice(..) => "binding",
PatKind::Wild
| PatKind::Never
| PatKind::Binding(..)
| PatKind::Path(..)
| PatKind::Box(..)
| PatKind::Deref(_)
| PatKind::Ref(..)
| PatKind::Lit(..)
| PatKind::Range(..)
| PatKind::Err(_) => break 'block None,
},
// Don't provide suggestions in other cases
_ => break 'block None,
};
Some((
pat.span,
format!("to declare a mutable {ident_kind} use"),
format!("mut {binding}"),
))
};
match binding_parent {
// Check that there is explicit type (ie this is not a closure param with inferred type)
// so we don't suggest moving something to the type that does not exist
hir::Node::Param(hir::Param { ty_span, pat, .. }) if pat.span != *ty_span => {
err.multipart_suggestion_verbose(
format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
vec![
(pat.span.until(inner.span), "".to_owned()),
(ty_span.shrink_to_lo(), mutbl.ref_prefix_str().to_owned()),
],
Applicability::MachineApplicable
);
if let Some((sp, msg, sugg)) = mut_var_suggestion {
err.span_note(sp, format!("{msg}: `{sugg}`"));
}
}
hir::Node::Pat(pt) if let PatKind::TupleStruct(_, pat_arr, _) = pt.kind => {
for i in pat_arr.iter() {
if let PatKind::Ref(the_ref, _) = i.kind
&& let PatKind::Binding(mt, _, ident, _) = the_ref.kind
{
let BindingMode(_, mtblty) = mt;
err.span_suggestion_verbose(
i.span,
format!("consider removing `&{mutability}` from the pattern"),
mtblty.prefix_str().to_string() + &ident.name.to_string(),
Applicability::MaybeIncorrect,
);
}
}
if let Some((sp, msg, sugg)) = mut_var_suggestion {
err.span_note(sp, format!("{msg}: `{sugg}`"));
}
}
hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
// rely on match ergonomics or it might be nested `&&pat`
err.span_suggestion_verbose(
pat.span.until(inner.span),
format!("consider removing `&{mutability}` from the pattern"),
"",
Applicability::MaybeIncorrect,
);
if let Some((sp, msg, sugg)) = mut_var_suggestion {
err.span_note(sp, format!("{msg}: `{sugg}`"));
}
}
_ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
}
_ => {} // don't provide suggestions in other cases #55175
}
}
}
pub fn check_dereferenceable(
&self,
span: Span,
expected: Ty<'tcx>,
inner: &Pat<'_>,
) -> Result<(), ErrorGuaranteed> {
if let PatKind::Binding(..) = inner.kind
&& let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
&& let ty::Dynamic(..) = mt.ty.kind()
{
// This is "x = dyn SomeTrait" being reduced from
// "let &x = &dyn SomeTrait" or "let box x = Box<dyn SomeTrait>", an error.
let type_str = self.ty_to_string(expected);
let mut err = struct_span_code_err!(
self.dcx(),
span,
E0033,
"type `{}` cannot be dereferenced",
type_str
);
err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
if self.tcx.sess.teach(err.code.unwrap()) {
err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
}
return Err(err.emit());
}
Ok(())
}
fn check_pat_struct(
&self,
pat: &'tcx Pat<'tcx>,
qpath: &hir::QPath<'tcx>,
fields: &'tcx [hir::PatField<'tcx>],
has_rest_pat: bool,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
// Resolve the path and check the definition for errors.
let (variant, pat_ty) = match self.check_struct_path(qpath, pat.hir_id) {
Ok(data) => data,
Err(guar) => {
let err = Ty::new_error(self.tcx, guar);
for field in fields {
self.check_pat(field.pat, err, pat_info);
}
return err;
}
};
// Type-check the path.
self.demand_eqtype_pat(pat.span, expected, pat_ty, pat_info.top_info);
// Type-check subpatterns.
if self.check_struct_pat_fields(pat_ty, pat, variant, fields, has_rest_pat, pat_info) {
pat_ty
} else {
Ty::new_misc_error(self.tcx)
}
}
fn check_pat_path(
&self,
pat: &Pat<'tcx>,
qpath: &hir::QPath<'_>,
path_resolution: (Res, Option<LoweredTy<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;
// We have already resolved the path.
let (res, opt_ty, segments) = path_resolution;
match res {
Res::Err => {
let e = tcx.dcx().span_delayed_bug(qpath.span(), "`Res::Err` but no error emitted");
self.set_tainted_by_errors(e);
return Ty::new_error(tcx, e);
}
Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::Variant, _) => {
let expected = "unit struct, unit variant or constant";
let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, E0533, expected);
return Ty::new_error(tcx, e);
}
Res::SelfCtor(def_id) => {
if let ty::Adt(adt_def, _) = *tcx.type_of(def_id).skip_binder().kind()
&& adt_def.is_struct()
&& let Some((CtorKind::Const, _)) = adt_def.non_enum_variant().ctor
{
// Ok, we allow unit struct ctors in patterns only.
} else {
let e = report_unexpected_variant_res(
tcx,
res,
qpath,
pat.span,
E0533,
"unit struct",
);
return Ty::new_error(tcx, e);
}
}
Res::Def(
DefKind::Ctor(_, CtorKind::Const)
| DefKind::Const
| DefKind::AssocConst
| DefKind::ConstParam,
_,
) => {} // OK
_ => bug!("unexpected pattern resolution: {:?}", res),
}
// Type-check the path.
let (pat_ty, pat_res) =
self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.span, pat.hir_id);
if let Some(err) =
self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
{
self.emit_bad_pat_path(err, pat, res, pat_res, pat_ty, segments);
}
pat_ty
}
fn maybe_suggest_range_literal(
&self,
e: &mut Diag<'_>,
opt_def_id: Option<hir::def_id::DefId>,
ident: Ident,
) -> bool {
match opt_def_id {
Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
Some(hir::Node::Item(hir::Item {
kind: hir::ItemKind::Const(_, _, body_id),
..
})) => match self.tcx.hir_node(body_id.hir_id) {
hir::Node::Expr(expr) => {
if hir::is_range_literal(expr) {
let span = self.tcx.hir().span(body_id.hir_id);
if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
e.span_suggestion_verbose(
ident.span,
"you may want to move the range into the match block",
snip,
Applicability::MachineApplicable,
);
return true;
}
}
}
_ => (),
},
_ => (),
},
_ => (),
}
false
}
fn emit_bad_pat_path(
&self,
mut e: Diag<'_>,
pat: &hir::Pat<'tcx>,
res: Res,
pat_res: Res,
pat_ty: Ty<'tcx>,
segments: &'tcx [hir::PathSegment<'tcx>],
) {
let pat_span = pat.span;
if let Some(span) = self.tcx.hir().res_span(pat_res) {
e.span_label(span, format!("{} defined here", res.descr()));
if let [hir::PathSegment { ident, .. }] = &*segments {
e.span_label(
pat_span,
format!(
"`{}` is interpreted as {} {}, not a new binding",
ident,
res.article(),
res.descr(),
),
);
match self.tcx.parent_hir_node(pat.hir_id) {
hir::Node::PatField(..) => {
e.span_suggestion_verbose(
ident.span.shrink_to_hi(),
"bind the struct field to a different name instead",
format!(": other_{}", ident.as_str().to_lowercase()),
Applicability::HasPlaceholders,
);
}
_ => {
let (type_def_id, item_def_id) = match pat_ty.kind() {
ty::Adt(def, _) => match res {
Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
_ => (None, None),
},
_ => (None, None),
};
let ranges = &[
self.tcx.lang_items().range_struct(),
self.tcx.lang_items().range_from_struct(),
self.tcx.lang_items().range_to_struct(),
self.tcx.lang_items().range_full_struct(),
self.tcx.lang_items().range_inclusive_struct(),
self.tcx.lang_items().range_to_inclusive_struct(),
];
if type_def_id != None && ranges.contains(&type_def_id) {
if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
let msg = "constants only support matching by type, \
if you meant to match against a range of values, \
consider using a range pattern like `min ..= max` in the match block";
e.note(msg);
}
} else {
let msg = "introduce a new binding instead";
let sugg = format!("other_{}", ident.as_str().to_lowercase());
e.span_suggestion(
ident.span,
msg,
sugg,
Applicability::HasPlaceholders,
);
}
}
};
}
}
e.emit();
}
fn check_pat_tuple_struct(
&self,
pat: &'tcx Pat<'tcx>,
qpath: &'tcx hir::QPath<'tcx>,
subpats: &'tcx [Pat<'tcx>],
ddpos: hir::DotDotPos,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let on_error = |e| {
for pat in subpats {
self.check_pat(pat, Ty::new_error(tcx, e), pat_info);
}
};
let report_unexpected_res = |res: Res| {
let expected = "tuple struct or tuple variant";
let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, E0164, expected);
on_error(e);
e
};
// Resolve the path and check the definition for errors.
let (res, opt_ty, segments) =
self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span, None);
if res == Res::Err {
let e = tcx.dcx().span_delayed_bug(pat.span, "`Res::Err` but no error emitted");
self.set_tainted_by_errors(e);
on_error(e);
return Ty::new_error(tcx, e);
}
// Type-check the path.
let (pat_ty, res) =
self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.span, pat.hir_id);
if !pat_ty.is_fn() {
let e = report_unexpected_res(res);
return Ty::new_error(tcx, e);
}
let variant = match res {
Res::Err => {
tcx.dcx().span_bug(pat.span, "`Res::Err` but no error emitted");
}
Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
let e = report_unexpected_res(res);
return Ty::new_error(tcx, e);
}
Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
_ => bug!("unexpected pattern resolution: {:?}", res),
};
// Replace constructor type with constructed type for tuple struct patterns.
let pat_ty = pat_ty.fn_sig(tcx).output();
let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
// Type-check the tuple struct pattern against the expected type.
let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, pat_info.top_info);
let had_err = if let Some(err) = diag {
err.emit();
true
} else {
false
};
// Type-check subpatterns.
if subpats.len() == variant.fields.len()
|| subpats.len() < variant.fields.len() && ddpos.as_opt_usize().is_some()
{
let ty::Adt(_, args) = pat_ty.kind() else {
bug!("unexpected pattern type {:?}", pat_ty);
};
for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
let field = &variant.fields[FieldIdx::from_usize(i)];
let field_ty = self.field_ty(subpat.span, field, args);
self.check_pat(subpat, field_ty, pat_info);
self.tcx.check_stability(
variant.fields[FieldIdx::from_usize(i)].did,
Some(pat.hir_id),
subpat.span,
None,
);
}
} else {
let e = self.emit_err_pat_wrong_number_of_fields(
pat.span,
res,
qpath,
subpats,
&variant.fields.raw,
expected,
had_err,
);
on_error(e);
return Ty::new_error(tcx, e);
}
pat_ty
}
fn emit_err_pat_wrong_number_of_fields(
&self,
pat_span: Span,
res: Res,
qpath: &hir::QPath<'_>,
subpats: &'tcx [Pat<'tcx>],
fields: &'tcx [ty::FieldDef],
expected: Ty<'tcx>,
had_err: bool,
) -> ErrorGuaranteed {
let subpats_ending = pluralize!(subpats.len());
let fields_ending = pluralize!(fields.len());
let subpat_spans = if subpats.is_empty() {
vec![pat_span]
} else {
subpats.iter().map(|p| p.span).collect()
};
let last_subpat_span = *subpat_spans.last().unwrap();
let res_span = self.tcx.def_span(res.def_id());
let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
let field_def_spans = if fields.is_empty() {
vec![res_span]
} else {
fields.iter().map(|f| f.ident(self.tcx).span).collect()
};
let last_field_def_span = *field_def_spans.last().unwrap();
let mut err = struct_span_code_err!(
self.dcx(),
MultiSpan::from_spans(subpat_spans),
E0023,
"this pattern has {} field{}, but the corresponding {} has {} field{}",
subpats.len(),
subpats_ending,
res.descr(),
fields.len(),
fields_ending,
);
err.span_label(
last_subpat_span,
format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
);
if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
err.span_label(qpath.span(), "");
}
if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
err.span_label(def_ident_span, format!("{} defined here", res.descr()));
}
for span in &field_def_spans[..field_def_spans.len() - 1] {
err.span_label(*span, "");
}
err.span_label(
last_field_def_span,
format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
);
// Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
// More generally, the expected type wants a tuple variant with one field of an
// N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
// with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
let missing_parentheses = match (&expected.kind(), fields, had_err) {
// #67037: only do this if we could successfully type-check the expected type against
// the tuple struct pattern. Otherwise the args could get out of range on e.g.,
// `let P() = U;` where `P != U` with `struct P<T>(T);`.
(ty::Adt(_, args), [field], false) => {
let field_ty = self.field_ty(pat_span, field, args);
match field_ty.kind() {
ty::Tuple(fields) => fields.len() == subpats.len(),
_ => false,
}
}
_ => false,
};
if missing_parentheses {
let (left, right) = match subpats {
// This is the zero case; we aim to get the "hi" part of the `QPath`'s
// span as the "lo" and then the "hi" part of the pattern's span as the "hi".
// This looks like:
//
// help: missing parentheses
// |
// L | let A(()) = A(());
// | ^ ^
[] => (qpath.span().shrink_to_hi(), pat_span),
// Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
// last sub-pattern. In the case of `A(x)` the first and last may coincide.
// This looks like:
//
// help: missing parentheses
// |
// L | let A((x, y)) = A((1, 2));
// | ^ ^
[first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
};
err.multipart_suggestion(
"missing parentheses",
vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
Applicability::MachineApplicable,
);
} else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
let all_fields_span = match subpats {
[] => after_fields_span,
[field] => field.span,
[first, .., last] => first.span.to(last.span),
};
// Check if all the fields in the pattern are wildcards.
let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
let first_tail_wildcard =
subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
(None, PatKind::Wild) => Some(pos),
(Some(_), PatKind::Wild) => acc,
_ => None,
});
let tail_span = match first_tail_wildcard {
None => after_fields_span,
Some(0) => subpats[0].span.to(after_fields_span),
Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
};
// FIXME: heuristic-based suggestion to check current types for where to add `_`.
let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
if !subpats.is_empty() {
wildcard_sugg = String::from(", ") + &wildcard_sugg;
}
err.span_suggestion_verbose(
after_fields_span,
"use `_` to explicitly ignore each field",
wildcard_sugg,
Applicability::MaybeIncorrect,
);
// Only suggest `..` if more than one field is missing
// or the pattern consists of all wildcards.
if fields.len() - subpats.len() > 1 || all_wildcards {
if subpats.is_empty() || all_wildcards {
err.span_suggestion_verbose(
all_fields_span,
"use `..` to ignore all fields",
"..",
Applicability::MaybeIncorrect,
);
} else {
err.span_suggestion_verbose(
tail_span,
"use `..` to ignore the rest of the fields",
", ..",
Applicability::MaybeIncorrect,
);
}
}
}
err.emit()
}
fn check_pat_tuple(
&self,
span: Span,
elements: &'tcx [Pat<'tcx>],
ddpos: hir::DotDotPos,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let mut expected_len = elements.len();
if ddpos.as_opt_usize().is_some() {
// Require known type only when `..` is present.
if let ty::Tuple(tys) = self.structurally_resolve_type(span, expected).kind() {
expected_len = tys.len();
}
}
let max_len = cmp::max(expected_len, elements.len());
let element_tys_iter =
(0..max_len).map(|_| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span }));
let element_tys = tcx.mk_type_list_from_iter(element_tys_iter);
let pat_ty = Ty::new_tup(tcx, element_tys);
if let Some(err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, pat_info.top_info) {
let reported = err.emit();
// Walk subpatterns with an expected type of `err` in this case to silence
// further errors being emitted when using the bindings. #50333
let element_tys_iter = (0..max_len).map(|_| Ty::new_error(tcx, reported));
for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
self.check_pat(elem, Ty::new_error(tcx, reported), pat_info);
}
Ty::new_tup_from_iter(tcx, element_tys_iter)
} else {
for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
self.check_pat(elem, element_tys[i], pat_info);
}
pat_ty
}
}
fn check_struct_pat_fields(
&self,
adt_ty: Ty<'tcx>,
pat: &'tcx Pat<'tcx>,
variant: &'tcx ty::VariantDef,
fields: &'tcx [hir::PatField<'tcx>],
has_rest_pat: bool,
pat_info: PatInfo<'tcx, '_>,
) -> bool {
let tcx = self.tcx;
let ty::Adt(adt, args) = adt_ty.kind() else {
span_bug!(pat.span, "struct pattern is not an ADT");
};
// Index the struct fields' types.
let field_map = variant
.fields
.iter_enumerated()
.map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
.collect::<FxHashMap<_, _>>();
// Keep track of which fields have already appeared in the pattern.
let mut used_fields = FxHashMap::default();
let mut no_field_errors = true;
let mut inexistent_fields = vec![];
// Typecheck each field.
for field in fields {
let span = field.span;
let ident = tcx.adjust_ident(field.ident, variant.def_id);
let field_ty = match used_fields.entry(ident) {
Occupied(occupied) => {
no_field_errors = false;
let guar = self.error_field_already_bound(span, field.ident, *occupied.get());
Ty::new_error(tcx, guar)
}
Vacant(vacant) => {
vacant.insert(span);
field_map
.get(&ident)
.map(|(i, f)| {
// FIXME: handle nested fields
self.write_field_index(field.hir_id, *i, Vec::new());
self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
self.field_ty(span, f, args)
})
.unwrap_or_else(|| {
inexistent_fields.push(field);
no_field_errors = false;
Ty::new_misc_error(tcx)
})
}
};
self.check_pat(field.pat, field_ty, pat_info);
}
let mut unmentioned_fields = variant
.fields
.iter()
.map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
.filter(|(_, ident)| !used_fields.contains_key(ident))
.collect::<Vec<_>>();
let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
&& !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
{
Some(self.error_inexistent_fields(
adt.variant_descr(),
&inexistent_fields,
&mut unmentioned_fields,
pat,
variant,
args,
))
} else {
None
};
// Require `..` if struct has non_exhaustive attribute.
let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
if non_exhaustive && !has_rest_pat {
self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
}
let mut unmentioned_err = None;
// Report an error if an incorrect number of fields was specified.
if adt.is_union() {
if fields.len() != 1 {
tcx.dcx().emit_err(errors::UnionPatMultipleFields { span: pat.span });
}
if has_rest_pat {
tcx.dcx().emit_err(errors::UnionPatDotDot { span: pat.span });
}
} else if !unmentioned_fields.is_empty() {
let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
.iter()
.copied()
.filter(|(field, _)| self.is_field_suggestable(field, pat.hir_id, pat.span))
.collect();
if !has_rest_pat {
if accessible_unmentioned_fields.is_empty() {
unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
} else {
unmentioned_err = Some(self.error_unmentioned_fields(
pat,
&accessible_unmentioned_fields,
accessible_unmentioned_fields.len() != unmentioned_fields.len(),
fields,
));
}
} else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
self.lint_non_exhaustive_omitted_patterns(
pat,
&accessible_unmentioned_fields,
adt_ty,
)
}
}
match (inexistent_fields_err, unmentioned_err) {
(Some(i), Some(u)) => {
if let Some(e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
// We don't want to show the nonexistent fields error when this was
// `Foo { a, b }` when it should have been `Foo(a, b)`.
i.delay_as_bug();
u.delay_as_bug();
e.emit();
} else {
i.emit();
u.emit();
}
}
(None, Some(u)) => {
if let Some(e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
u.delay_as_bug();
e.emit();
} else {
u.emit();
}
}
(Some(err), None) => {
err.emit();
}
(None, None)
if let Some(err) =
self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
{
err.emit();
}
(None, None) => {}
}
no_field_errors
}
fn error_tuple_variant_index_shorthand(
&self,
variant: &VariantDef,
pat: &'_ Pat<'_>,
fields: &[hir::PatField<'_>],
) -> Option<Diag<'_>> {
// if this is a tuple struct, then all field names will be numbers
// so if any fields in a struct pattern use shorthand syntax, they will
// be invalid identifiers (for example, Foo { 0, 1 }).
if let (Some(CtorKind::Fn), PatKind::Struct(qpath, field_patterns, ..)) =
(variant.ctor_kind(), &pat.kind)
{
let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
if has_shorthand_field_name {
let path = rustc_hir_pretty::qpath_to_string(&self.tcx, qpath);
let mut err = struct_span_code_err!(
self.dcx(),
pat.span,
E0769,
"tuple variant `{path}` written as struct variant",
);
err.span_suggestion_verbose(
qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
"use the tuple variant pattern syntax instead",
format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
Applicability::MaybeIncorrect,
);
return Some(err);
}
}
None
}
fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
let sess = self.tcx.sess;
let sm = sess.source_map();
let sp_brace = sm.end_point(pat.span);
let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
struct_span_code_err!(
self.dcx(),
pat.span,
E0638,
"`..` required with {descr} marked as non-exhaustive",
)
.with_span_suggestion_verbose(
sp_comma,
"add `..` at the end of the field list to ignore all other fields",
sugg,
Applicability::MachineApplicable,
)
.emit();
}
fn error_field_already_bound(
&self,
span: Span,
ident: Ident,
other_field: Span,
) -> ErrorGuaranteed {
struct_span_code_err!(
self.dcx(),
span,
E0025,
"field `{}` bound multiple times in the pattern",
ident
)
.with_span_label(span, format!("multiple uses of `{ident}` in pattern"))
.with_span_label(other_field, format!("first use of `{ident}`"))
.emit()
}
fn error_inexistent_fields(
&self,
kind_name: &str,
inexistent_fields: &[&hir::PatField<'tcx>],
unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
pat: &'tcx Pat<'tcx>,
variant: &ty::VariantDef,
args: &'tcx ty::List<ty::GenericArg<'tcx>>,
) -> Diag<'tcx> {
let tcx = self.tcx;
let (field_names, t, plural) = if let [field] = inexistent_fields {
(format!("a field named `{}`", field.ident), "this", "")
} else {
(
format!(
"fields named {}",
inexistent_fields
.iter()
.map(|field| format!("`{}`", field.ident))
.collect::<Vec<String>>()
.join(", ")
),
"these",
"s",
)
};
let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
let mut err = struct_span_code_err!(
tcx.dcx(),
spans,
E0026,
"{} `{}` does not have {}",
kind_name,
tcx.def_path_str(variant.def_id),
field_names
);
if let Some(pat_field) = inexistent_fields.last() {
err.span_label(
pat_field.ident.span,
format!(
"{} `{}` does not have {} field{}",
kind_name,
tcx.def_path_str(variant.def_id),
t,
plural
),
);
if let [(field_def, field)] = unmentioned_fields.as_slice()
&& self.is_field_suggestable(field_def, pat.hir_id, pat.span)
{
let suggested_name =
find_best_match_for_name(&[field.name], pat_field.ident.name, None);
if let Some(suggested_name) = suggested_name {
err.span_suggestion(
pat_field.ident.span,
"a field with a similar name exists",
suggested_name,
Applicability::MaybeIncorrect,
);
// When we have a tuple struct used with struct we don't want to suggest using
// the (valid) struct syntax with numeric field names. Instead we want to
// suggest the expected syntax. We infer that this is the case by parsing the
// `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
// `smart_resolve_context_dependent_help`.
if suggested_name.to_ident_string().parse::<usize>().is_err() {
// We don't want to throw `E0027` in case we have thrown `E0026` for them.
unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
}
} else if inexistent_fields.len() == 1 {
match pat_field.pat.kind {
PatKind::Lit(expr)
if !self.can_coerce(
self.typeck_results.borrow().expr_ty(expr),
self.field_ty(field.span, field_def, args),
) => {}
_ => {
err.span_suggestion_short(
pat_field.ident.span,
format!(
"`{}` has a field named `{}`",
tcx.def_path_str(variant.def_id),
field.name,
),
field.name,
Applicability::MaybeIncorrect,
);
}
}
}
}
}
if tcx.sess.teach(err.code.unwrap()) {
err.note(
"This error indicates that a struct pattern attempted to \
extract a nonexistent field from a struct. Struct fields \
are identified by the name used before the colon : so struct \
patterns should resemble the declaration of the struct type \
being matched.\n\n\
If you are using shorthand field patterns but want to refer \
to the struct field by a different name, you should rename \
it explicitly.",
);
}
err
}
fn error_tuple_variant_as_struct_pat(
&self,
pat: &Pat<'_>,
fields: &'tcx [hir::PatField<'tcx>],
variant: &ty::VariantDef,
) -> Option<Diag<'tcx>> {
if let (Some(CtorKind::Fn), PatKind::Struct(qpath, pattern_fields, ..)) =
(variant.ctor_kind(), &pat.kind)
{
let is_tuple_struct_match = !pattern_fields.is_empty()
&& pattern_fields.iter().map(|field| field.ident.name.as_str()).all(is_number);
if is_tuple_struct_match {
return None;
}
let path = rustc_hir_pretty::qpath_to_string(&self.tcx, qpath);
let mut err = struct_span_code_err!(
self.dcx(),
pat.span,
E0769,
"tuple variant `{}` written as struct variant",
path
);
let (sugg, appl) = if fields.len() == variant.fields.len() {
(
self.get_suggested_tuple_struct_pattern(fields, variant),
Applicability::MachineApplicable,
)
} else {
(
variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
Applicability::MaybeIncorrect,
)
};
err.span_suggestion_verbose(
qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
"use the tuple variant pattern syntax instead",
format!("({sugg})"),
appl,
);
return Some(err);
}
None
}
fn get_suggested_tuple_struct_pattern(
&self,
fields: &[hir::PatField<'_>],
variant: &VariantDef,
) -> String {
let variant_field_idents =
variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
fields
.iter()
.map(|field| {
match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
Ok(f) => {
// Field names are numbers, but numbers
// are not valid identifiers
if variant_field_idents.contains(&field.ident) {
String::from("_")
} else {
f
}
}
Err(_) => rustc_hir_pretty::pat_to_string(&self.tcx, field.pat),
}
})
.collect::<Vec<String>>()
.join(", ")
}
/// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
/// inaccessible fields.
///
/// ```text
/// error: pattern requires `..` due to inaccessible fields
/// --> src/main.rs:10:9
/// |
/// LL | let foo::Foo {} = foo::Foo::default();
/// | ^^^^^^^^^^^
/// |
/// help: add a `..`
/// |
/// LL | let foo::Foo { .. } = foo::Foo::default();
/// | ^^^^^^
/// ```
fn error_no_accessible_fields(
&self,
pat: &Pat<'_>,
fields: &'tcx [hir::PatField<'tcx>],
) -> Diag<'tcx> {
let mut err = self
.dcx()
.struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
if let Some(field) = fields.last() {
err.span_suggestion_verbose(
field.span.shrink_to_hi(),
"ignore the inaccessible and unused fields",
", ..",
Applicability::MachineApplicable,
);
} else {
let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
qpath.span()
} else {
bug!("`error_no_accessible_fields` called on non-struct pattern");
};
// Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
err.span_suggestion_verbose(
span,
"ignore the inaccessible and unused fields",
" { .. }",
Applicability::MachineApplicable,
);
}
err
}
/// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
/// is not exhaustive enough.
///
/// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
fn lint_non_exhaustive_omitted_patterns(
&self,
pat: &Pat<'_>,
unmentioned_fields: &[(&ty::FieldDef, Ident)],
ty: Ty<'tcx>,
) {
fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
const LIMIT: usize = 3;
match witnesses {
[] => {
unreachable!(
"expected an uncovered pattern, otherwise why are we emitting an error?"
)
}
[witness] => format!("`{witness}`"),
[head @ .., tail] if head.len() < LIMIT => {
let head: Vec<_> = head.iter().map(<_>::to_string).collect();
format!("`{}` and `{}`", head.join("`, `"), tail)
}
_ => {
let (head, tail) = witnesses.split_at(LIMIT);
let head: Vec<_> = head.iter().map(<_>::to_string).collect();
format!("`{}` and {} more", head.join("`, `"), tail.len())
}
}
}
let joined_patterns = joined_uncovered_patterns(
&unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
);
self.tcx.node_span_lint(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, "some fields are not explicitly listed", |lint| {
lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
lint.help(
"ensure that all fields are mentioned explicitly by adding the suggested fields",
);
lint.note(format!(
"the pattern is of type `{ty}` and the `non_exhaustive_omitted_patterns` attribute was found",
));
});
}
/// Returns a diagnostic reporting a struct pattern which does not mention some fields.
///
/// ```text
/// error[E0027]: pattern does not mention field `bar`
/// --> src/main.rs:15:9
/// |
/// LL | let foo::Foo {} = foo::Foo::new();
/// | ^^^^^^^^^^^ missing field `bar`
/// ```
fn error_unmentioned_fields(
&self,
pat: &Pat<'_>,
unmentioned_fields: &[(&ty::FieldDef, Ident)],
have_inaccessible_fields: bool,
fields: &'tcx [hir::PatField<'tcx>],
) -> Diag<'tcx> {
let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
let field_names = if let [(_, field)] = unmentioned_fields {
format!("field `{field}`{inaccessible}")
} else {
let fields = unmentioned_fields
.iter()
.map(|(_, name)| format!("`{name}`"))
.collect::<Vec<String>>()
.join(", ");
format!("fields {fields}{inaccessible}")
};
let mut err = struct_span_code_err!(
self.dcx(),
pat.span,
E0027,
"pattern does not mention {}",
field_names
);
err.span_label(pat.span, format!("missing {field_names}"));
let len = unmentioned_fields.len();
let (prefix, postfix, sp) = match fields {
[] => match &pat.kind {
PatKind::Struct(path, [], false) => {
(" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
}
_ => return err,
},
[.., field] => {
// Account for last field having a trailing comma or parse recovery at the tail of
// the pattern to avoid invalid suggestion (#78511).
let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
match &pat.kind {
PatKind::Struct(..) => (", ", " }", tail),
_ => return err,
}
}
};
err.span_suggestion(
sp,
format!(
"include the missing field{} in the pattern{}",
pluralize!(len),
if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
),
format!(
"{}{}{}{}",
prefix,
unmentioned_fields
.iter()
.map(|(_, name)| {
let field_name = name.to_string();
if is_number(&field_name) { format!("{field_name}: _") } else { field_name }
})
.collect::<Vec<_>>()
.join(", "),
if have_inaccessible_fields { ", .." } else { "" },
postfix,
),
Applicability::MachineApplicable,
);
err.span_suggestion(
sp,
format!(
"if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
these = pluralize!("this", len),
s = pluralize!(len),
them = if len == 1 { "it" } else { "them" },
),
format!("{prefix}..{postfix}"),
Applicability::MachineApplicable,
);
err
}
fn check_pat_box(
&self,
span: Span,
inner: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let (box_ty, inner_ty) = match self.check_dereferenceable(span, expected, inner) {
Ok(()) => {
// Here, `demand::subtype` is good enough, but I don't
// think any errors can be introduced by using `demand::eqtype`.
let inner_ty =
self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: inner.span });
let box_ty = Ty::new_box(tcx, inner_ty);
self.demand_eqtype_pat(span, expected, box_ty, pat_info.top_info);
(box_ty, inner_ty)
}
Err(guar) => {
let err = Ty::new_error(tcx, guar);
(err, err)
}
};
self.check_pat(inner, inner_ty, pat_info);
box_ty
}
fn check_pat_deref(
&self,
span: Span,
inner: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let tcx = self.tcx;
// Register a `DerefPure` bound, which is required by all `deref!()` pats.
self.register_bound(
expected,
tcx.require_lang_item(hir::LangItem::DerefPure, Some(span)),
self.misc(span),
);
// <expected as Deref>::Target
let ty = Ty::new_projection(
tcx,
tcx.require_lang_item(hir::LangItem::DerefTarget, Some(span)),
[expected],
);
let ty = self.normalize(span, ty);
let ty = self.try_structurally_resolve_type(span, ty);
self.check_pat(inner, ty, pat_info);
// Check if the pattern has any `ref mut` bindings, which would require
// `DerefMut` to be emitted in MIR building instead of just `Deref`.
// We do this *after* checking the inner pattern, since we want to make
// sure to apply any match-ergonomics adjustments.
if self.typeck_results.borrow().pat_has_ref_mut_binding(inner) {
self.register_bound(
expected,
tcx.require_lang_item(hir::LangItem::DerefMut, Some(span)),
self.misc(span),
);
}
expected
}
// Precondition: Pat is Ref(inner)
fn check_pat_ref(
&self,
pat: &'tcx Pat<'tcx>,
inner: &'tcx Pat<'tcx>,
mutbl: Mutability,
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
consumed_inherited_ref: bool,
) -> Ty<'tcx> {
if consumed_inherited_ref
&& pat.span.at_least_rust_2024()
&& self.tcx.features().ref_pat_eat_one_layer_2024
{
self.typeck_results.borrow_mut().skipped_ref_pats_mut().insert(pat.hir_id);
self.check_pat(inner, expected, pat_info);
expected
} else {
let tcx = self.tcx;
let expected = self.shallow_resolve(expected);
let (ref_ty, inner_ty) = match self.check_dereferenceable(pat.span, expected, inner) {
Ok(()) => {
// `demand::subtype` would be good enough, but using `eqtype` turns
// out to be equally general. See (note_1) for details.
// Take region, inner-type from expected type if we can,
// to avoid creating needless variables. This also helps with
// the bad interactions of the given hack detailed in (note_1).
debug!("check_pat_ref: expected={:?}", expected);
match *expected.kind() {
ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
_ => {
if consumed_inherited_ref && self.tcx.features().ref_pat_everywhere {
// We already matched against a match-ergonmics inserted reference,
// so we don't need to match against a reference from the original type.
// Save this infor for use in lowering later
self.typeck_results
.borrow_mut()
.skipped_ref_pats_mut()
.insert(pat.hir_id);
(expected, expected)
} else {
let inner_ty = self.next_ty_var(TypeVariableOrigin {
param_def_id: None,
span: inner.span,
});
let ref_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
debug!("check_pat_ref: demanding {:?} = {:?}", expected, ref_ty);
let err = self.demand_eqtype_pat_diag(
pat.span,
expected,
ref_ty,
pat_info.top_info,
);
// Look for a case like `fn foo(&foo: u32)` and suggest
// `fn foo(foo: &u32)`
if let Some(mut err) = err {
self.borrow_pat_suggestion(&mut err, pat);
err.emit();
}
(ref_ty, inner_ty)
}
}
}
}
Err(guar) => {
let err = Ty::new_error(tcx, guar);
(err, err)
}
};
self.check_pat(inner, inner_ty, pat_info);
ref_ty
}
}
/// Create a reference type with a fresh region variable.
fn new_ref_ty(&self, span: Span, mutbl: Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
let region = self.next_region_var(infer::PatternRegion(span));
Ty::new_ref(self.tcx, region, ty, mutbl)
}
fn try_resolve_slice_ty_to_array_ty(
&self,
before: &'tcx [Pat<'tcx>],
slice: Option<&'tcx Pat<'tcx>>,
span: Span,
) -> Option<Ty<'tcx>> {
if slice.is_some() {
return None;
}
let tcx = self.tcx;
let len = before.len();
let ty_var_origin = TypeVariableOrigin { param_def_id: None, span };
let inner_ty = self.next_ty_var(ty_var_origin);
Some(Ty::new_array(tcx, inner_ty, len.try_into().unwrap()))
}
/// Used to determines whether we can infer the expected type in the slice pattern to be of type array.
/// This is only possible if we're in an irrefutable pattern. If we were to allow this in refutable
/// patterns we wouldn't e.g. report ambiguity in the following situation:
///
/// ```ignore(rust)
/// struct Zeroes;
/// const ARR: [usize; 2] = [0; 2];
/// const ARR2: [usize; 2] = [2; 2];
///
/// impl Into<&'static [usize; 2]> for Zeroes {
/// fn into(self) -> &'static [usize; 2] {
/// &ARR
/// }
/// }
///
/// impl Into<&'static [usize]> for Zeroes {
/// fn into(self) -> &'static [usize] {
/// &ARR2
/// }
/// }
///
/// fn main() {
/// let &[a, b]: &[usize] = Zeroes.into() else {
/// ..
/// };
/// }
/// ```
///
/// If we're in an irrefutable pattern we prefer the array impl candidate given that
/// the slice impl candidate would be rejected anyway (if no ambiguity existed).
fn pat_is_irrefutable(&self, decl_origin: Option<DeclOrigin<'_>>) -> bool {
match decl_origin {
Some(DeclOrigin::LocalDecl { els: None }) => true,
Some(DeclOrigin::LocalDecl { els: Some(_) } | DeclOrigin::LetExpr) | None => false,
}
}
/// Type check a slice pattern.
///
/// Syntactically, these look like `[pat_0, ..., pat_n]`.
/// Semantically, we are type checking a pattern with structure:
/// ```ignore (not-rust)
/// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
/// ```
/// The type of `slice`, if it is present, depends on the `expected` type.
/// If `slice` is missing, then so is `after_i`.
/// If `slice` is present, it can still represent 0 elements.
fn check_pat_slice(
&self,
span: Span,
before: &'tcx [Pat<'tcx>],
slice: Option<&'tcx Pat<'tcx>>,
after: &'tcx [Pat<'tcx>],
expected: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
let expected = self.try_structurally_resolve_type(span, expected);
// If the pattern is irrefutable and `expected` is an infer ty, we try to equate it
// to an array if the given pattern allows it. See issue #76342
if self.pat_is_irrefutable(pat_info.decl_origin) && expected.is_ty_var() {
if let Some(resolved_arr_ty) =
self.try_resolve_slice_ty_to_array_ty(before, slice, span)
{
debug!(?resolved_arr_ty);
self.demand_eqtype(span, expected, resolved_arr_ty);
}
}
let expected = self.structurally_resolve_type(span, expected);
debug!(?expected);
let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
// An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
ty::Array(element_ty, len) => {
let min = before.len() as u64 + after.len() as u64;
let (opt_slice_ty, expected) =
self.check_array_pat_len(span, element_ty, expected, slice, len, min);
// `opt_slice_ty.is_none()` => `slice.is_none()`.
// Note, though, that opt_slice_ty could be `Some(error_ty)`.
assert!(opt_slice_ty.is_some() || slice.is_none());
(element_ty, opt_slice_ty, expected)
}
ty::Slice(element_ty) => (element_ty, Some(expected), expected),
// The expected type must be an array or slice, but was neither, so error.
_ => {
let guar = expected.error_reported().err().unwrap_or_else(|| {
self.error_expected_array_or_slice(span, expected, pat_info)
});
let err = Ty::new_error(self.tcx, guar);
(err, Some(err), err)
}
};
// Type check all the patterns before `slice`.
for elt in before {
self.check_pat(elt, element_ty, pat_info);
}
// Type check the `slice`, if present, against its expected type.
if let Some(slice) = slice {
self.check_pat(slice, opt_slice_ty.unwrap(), pat_info);
}
// Type check the elements after `slice`, if present.
for elt in after {
self.check_pat(elt, element_ty, pat_info);
}
inferred
}
/// Type check the length of an array pattern.
///
/// Returns both the type of the variable length pattern (or `None`), and the potentially
/// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
fn check_array_pat_len(
&self,
span: Span,
element_ty: Ty<'tcx>,
arr_ty: Ty<'tcx>,
slice: Option<&'tcx Pat<'tcx>>,
len: ty::Const<'tcx>,
min_len: u64,
) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
let len = match len.eval(self.tcx, self.param_env, span) {
Ok(val) => val
.try_to_scalar()
.and_then(|scalar| scalar.try_to_int().ok())
.and_then(|int| int.try_to_target_usize(self.tcx).ok()),
Err(ErrorHandled::Reported(..)) => {
let guar = self.error_scrutinee_unfixed_length(span);
return (Some(Ty::new_error(self.tcx, guar)), arr_ty);
}
Err(ErrorHandled::TooGeneric(..)) => None,
};
let guar = if let Some(len) = len {
// Now we know the length...
if slice.is_none() {
// ...and since there is no variable-length pattern,
// we require an exact match between the number of elements
// in the array pattern and as provided by the matched type.
if min_len == len {
return (None, arr_ty);
}
self.error_scrutinee_inconsistent_length(span, min_len, len)
} else if let Some(pat_len) = len.checked_sub(min_len) {
// The variable-length pattern was there,
// so it has an array type with the remaining elements left as its size...
return (Some(Ty::new_array(self.tcx, element_ty, pat_len)), arr_ty);
} else {
// ...however, in this case, there were no remaining elements.
// That is, the slice pattern requires more than the array type offers.
self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len)
}
} else if slice.is_none() {
// We have a pattern with a fixed length,
// which we can use to infer the length of the array.
let updated_arr_ty = Ty::new_array(self.tcx, element_ty, min_len);
self.demand_eqtype(span, updated_arr_ty, arr_ty);
return (None, updated_arr_ty);
} else {
// We have a variable-length pattern and don't know the array length.
// This happens if we have e.g.,
// `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
self.error_scrutinee_unfixed_length(span)
};
// If we get here, we must have emitted an error.
(Some(Ty::new_error(self.tcx, guar)), arr_ty)
}
fn error_scrutinee_inconsistent_length(
&self,
span: Span,
min_len: u64,
size: u64,
) -> ErrorGuaranteed {
struct_span_code_err!(
self.dcx(),
span,
E0527,
"pattern requires {} element{} but array has {}",
min_len,
pluralize!(min_len),
size,
)
.with_span_label(span, format!("expected {} element{}", size, pluralize!(size)))
.emit()
}
fn error_scrutinee_with_rest_inconsistent_length(
&self,
span: Span,
min_len: u64,
size: u64,
) -> ErrorGuaranteed {
struct_span_code_err!(
self.dcx(),
span,
E0528,
"pattern requires at least {} element{} but array has {}",
min_len,
pluralize!(min_len),
size,
)
.with_span_label(
span,
format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
)
.emit()
}
fn error_scrutinee_unfixed_length(&self, span: Span) -> ErrorGuaranteed {
struct_span_code_err!(
self.dcx(),
span,
E0730,
"cannot pattern-match on an array without a fixed length",
)
.emit()
}
fn error_expected_array_or_slice(
&self,
span: Span,
expected_ty: Ty<'tcx>,
pat_info: PatInfo<'tcx, '_>,
) -> ErrorGuaranteed {
let PatInfo { top_info: ti, current_depth, .. } = pat_info;
let mut err = struct_span_code_err!(
self.dcx(),
span,
E0529,
"expected an array or slice, found `{expected_ty}`"
);
if let ty::Ref(_, ty, _) = expected_ty.kind()
&& let ty::Array(..) | ty::Slice(..) = ty.kind()
{
err.help("the semantics of slice patterns changed recently; see issue #62254");
} else if self
.autoderef(span, expected_ty)
.any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
&& let Some(span) = ti.span
&& let Some(_) = ti.origin_expr
&& let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
{
let resolved_ty = self.resolve_vars_if_possible(ti.expected);
let (is_slice_or_array_or_vector, resolved_ty) =
self.is_slice_or_array_or_vector(resolved_ty);
match resolved_ty.kind() {
ty::Adt(adt_def, _)
if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
|| self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
{
// Slicing won't work here, but `.as_deref()` might (issue #91328).
err.span_suggestion(
span,
"consider using `as_deref` here",
format!("{snippet}.as_deref()"),
Applicability::MaybeIncorrect,
);
}
_ => (),
}
let is_top_level = current_depth <= 1;
if is_slice_or_array_or_vector && is_top_level {
err.span_suggestion(
span,
"consider slicing here",
format!("{snippet}[..]"),
Applicability::MachineApplicable,
);
}
}
err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
err.emit()
}
fn is_slice_or_array_or_vector(&self, ty: Ty<'tcx>) -> (bool, Ty<'tcx>) {
match ty.kind() {
ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
(true, ty)
}
ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(*ty),
ty::Slice(..) | ty::Array(..) => (true, ty),
_ => (false, ty),
}
}
}