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fuchsia / third_party / rust / 57e8fc56852e7728d7160242bf13c3ab6e066bd8 / . / compiler / rustc_typeck / src / astconv / mod.rs
blob: 46b8b2e14c7363daef2709978e325d58066ae5d9 [file] [log] [blame]
//! Conversion from AST representation of types to the `ty.rs` representation.
//! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
//! instance of `AstConv`.
mod errors;
mod generics;
use crate::bounds::Bounds;
use crate::collect::PlaceholderHirTyCollector;
use crate::errors::{
AmbiguousLifetimeBound, MultipleRelaxedDefaultBounds, TraitObjectDeclaredWithNoTraits,
TypeofReservedKeywordUsed, ValueOfAssociatedStructAlreadySpecified,
};
use crate::middle::resolve_lifetime as rl;
use crate::require_c_abi_if_c_variadic;
use rustc_ast::util::lev_distance::find_best_match_for_name;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::{struct_span_err, Applicability, ErrorReported, FatalError};
use rustc_hir as hir;
use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::{walk_generics, Visitor as _};
use rustc_hir::lang_items::LangItem;
use rustc_hir::{Constness, GenericArg, GenericArgs};
use rustc_middle::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
use rustc_middle::ty::GenericParamDefKind;
use rustc_middle::ty::{self, Const, DefIdTree, Ty, TyCtxt, TypeFoldable};
use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
use rustc_span::symbol::{Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use rustc_target::spec::abi;
use rustc_trait_selection::traits;
use rustc_trait_selection::traits::astconv_object_safety_violations;
use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
use rustc_trait_selection::traits::wf::object_region_bounds;
use smallvec::SmallVec;
use std::collections::BTreeSet;
use std::iter;
use std::slice;
#[derive(Debug)]
pub struct PathSeg(pub DefId, pub usize);
pub trait AstConv<'tcx> {
fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
fn item_def_id(&self) -> Option<DefId>;
fn default_constness_for_trait_bounds(&self) -> Constness;
/// Returns predicates in scope of the form `X: Foo`, where `X` is
/// a type parameter `X` with the given id `def_id`. This is a
/// subset of the full set of predicates.
///
/// This is used for one specific purpose: resolving "short-hand"
/// associated type references like `T::Item`. In principle, we
/// would do that by first getting the full set of predicates in
/// scope and then filtering down to find those that apply to `T`,
/// but this can lead to cycle errors. The problem is that we have
/// to do this resolution *in order to create the predicates in
/// the first place*. Hence, we have this "special pass".
fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
/// Returns the lifetime to use when a lifetime is omitted (and not elided).
fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
-> Option<ty::Region<'tcx>>;
/// Returns the type to use when a type is omitted.
fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
/// Returns `true` if `_` is allowed in type signatures in the current context.
fn allow_ty_infer(&self) -> bool;
/// Returns the const to use when a const is omitted.
fn ct_infer(
&self,
ty: Ty<'tcx>,
param: Option<&ty::GenericParamDef>,
span: Span,
) -> &'tcx Const<'tcx>;
/// Projecting an associated type from a (potentially)
/// higher-ranked trait reference is more complicated, because of
/// the possibility of late-bound regions appearing in the
/// associated type binding. This is not legal in function
/// signatures for that reason. In a function body, we can always
/// handle it because we can use inference variables to remove the
/// late-bound regions.
fn projected_ty_from_poly_trait_ref(
&self,
span: Span,
item_def_id: DefId,
item_segment: &hir::PathSegment<'_>,
poly_trait_ref: ty::PolyTraitRef<'tcx>,
) -> Ty<'tcx>;
/// Normalize an associated type coming from the user.
fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
/// Invoked when we encounter an error from some prior pass
/// (e.g., resolve) that is translated into a ty-error. This is
/// used to help suppress derived errors typeck might otherwise
/// report.
fn set_tainted_by_errors(&self);
fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
}
pub enum SizedByDefault {
Yes,
No,
}
struct ConvertedBinding<'a, 'tcx> {
item_name: Ident,
kind: ConvertedBindingKind<'a, 'tcx>,
span: Span,
}
enum ConvertedBindingKind<'a, 'tcx> {
Equality(Ty<'tcx>),
Constraint(&'a [hir::GenericBound<'a>]),
}
/// New-typed boolean indicating whether explicit late-bound lifetimes
/// are present in a set of generic arguments.
///
/// For example if we have some method `fn f<'a>(&'a self)` implemented
/// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
/// is late-bound so should not be provided explicitly. Thus, if `f` is
/// instantiated with some generic arguments providing `'a` explicitly,
/// we taint those arguments with `ExplicitLateBound::Yes` so that we
/// can provide an appropriate diagnostic later.
#[derive(Copy, Clone, PartialEq)]
pub enum ExplicitLateBound {
Yes,
No,
}
/// Denotes the "position" of a generic argument, indicating if it is a generic type,
/// generic function or generic method call.
#[derive(Copy, Clone, PartialEq)]
pub(crate) enum GenericArgPosition {
Type,
Value, // e.g., functions
MethodCall,
}
/// A marker denoting that the generic arguments that were
/// provided did not match the respective generic parameters.
#[derive(Clone, Default)]
pub struct GenericArgCountMismatch {
/// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
pub reported: Option<ErrorReported>,
/// A list of spans of arguments provided that were not valid.
pub invalid_args: Vec<Span>,
}
/// Decorates the result of a generic argument count mismatch
/// check with whether explicit late bounds were provided.
#[derive(Clone)]
pub struct GenericArgCountResult {
pub explicit_late_bound: ExplicitLateBound,
pub correct: Result<(), GenericArgCountMismatch>,
}
impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
pub fn ast_region_to_region(
&self,
lifetime: &hir::Lifetime,
def: Option<&ty::GenericParamDef>,
) -> ty::Region<'tcx> {
let tcx = self.tcx();
let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
let r = match tcx.named_region(lifetime.hir_id) {
Some(rl::Region::Static) => tcx.lifetimes.re_static,
Some(rl::Region::LateBound(debruijn, id, _)) => {
let name = lifetime_name(id.expect_local());
tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
}
Some(rl::Region::LateBoundAnon(debruijn, index)) => {
tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
}
Some(rl::Region::EarlyBound(index, id, _)) => {
let name = lifetime_name(id.expect_local());
tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
}
Some(rl::Region::Free(scope, id)) => {
let name = lifetime_name(id.expect_local());
tcx.mk_region(ty::ReFree(ty::FreeRegion {
scope,
bound_region: ty::BrNamed(id, name),
}))
// (*) -- not late-bound, won't change
}
None => {
self.re_infer(def, lifetime.span).unwrap_or_else(|| {
// This indicates an illegal lifetime
// elision. `resolve_lifetime` should have
// reported an error in this case -- but if
// not, let's error out.
tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
// Supply some dummy value. We don't have an
// `re_error`, annoyingly, so use `'static`.
tcx.lifetimes.re_static
})
}
};
debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
r
}
/// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
/// returns an appropriate set of substitutions for this particular reference to `I`.
pub fn ast_path_substs_for_ty(
&self,
span: Span,
def_id: DefId,
item_segment: &hir::PathSegment<'_>,
) -> SubstsRef<'tcx> {
let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
span,
def_id,
&[],
item_segment.generic_args(),
item_segment.infer_args,
None,
);
if let Some(b) = assoc_bindings.first() {
Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
}
substs
}
/// Given the type/lifetime/const arguments provided to some path (along with
/// an implicit `Self`, if this is a trait reference), returns the complete
/// set of substitutions. This may involve applying defaulted type parameters.
/// Also returns back constraints on associated types.
///
/// Example:
///
/// ```
/// T: std::ops::Index<usize, Output = u32>
/// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
/// ```
///
/// 1. The `self_ty` here would refer to the type `T`.
/// 2. The path in question is the path to the trait `std::ops::Index`,
/// which will have been resolved to a `def_id`
/// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
/// parameters are returned in the `SubstsRef`, the associated type bindings like
/// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
///
/// Note that the type listing given here is *exactly* what the user provided.
///
/// For (generic) associated types
///
/// ```
/// <Vec<u8> as Iterable<u8>>::Iter::<'a>
/// ```
///
/// We have the parent substs are the substs for the parent trait:
/// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
/// type itself: `['a]`. The returned `SubstsRef` concatenates these two
/// lists: `[Vec<u8>, u8, 'a]`.
fn create_substs_for_ast_path<'a>(
&self,
span: Span,
def_id: DefId,
parent_substs: &[subst::GenericArg<'tcx>],
generic_args: &'a hir::GenericArgs<'_>,
infer_args: bool,
self_ty: Option<Ty<'tcx>>,
) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
// If the type is parameterized by this region, then replace this
// region with the current anon region binding (in other words,
// whatever & would get replaced with).
debug!(
"create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
generic_args={:?})",
def_id, self_ty, generic_args
);
let tcx = self.tcx();
let generic_params = tcx.generics_of(def_id);
if generic_params.has_self {
if generic_params.parent.is_some() {
// The parent is a trait so it should have at least one subst
// for the `Self` type.
assert!(!parent_substs.is_empty())
} else {
// This item (presumably a trait) needs a self-type.
assert!(self_ty.is_some());
}
} else {
assert!(self_ty.is_none() && parent_substs.is_empty());
}
let arg_count = Self::check_generic_arg_count(
tcx,
span,
&generic_params,
&generic_args,
GenericArgPosition::Type,
self_ty.is_some(),
infer_args,
);
let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
let default_needs_object_self = |param: &ty::GenericParamDef| {
if let GenericParamDefKind::Type { has_default, .. } = param.kind {
if is_object && has_default {
let default_ty = tcx.at(span).type_of(param.def_id);
let self_param = tcx.types.self_param;
if default_ty.walk().any(|arg| arg == self_param.into()) {
// There is no suitable inference default for a type parameter
// that references self, in an object type.
return true;
}
}
}
false
};
let mut missing_type_params = vec![];
let mut inferred_params = vec![];
let substs = Self::create_substs_for_generic_args(
tcx,
def_id,
parent_substs,
self_ty.is_some(),
self_ty,
arg_count.clone(),
// Provide the generic args, and whether types should be inferred.
|did| {
if did == def_id {
(Some(generic_args), infer_args)
} else {
// The last component of this tuple is unimportant.
(None, false)
}
},
// Provide substitutions for parameters for which (valid) arguments have been provided.
|param, arg| match (&param.kind, arg) {
(GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
self.ast_region_to_region(&lt, Some(param)).into()
}
(GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
if *has_default {
tcx.check_optional_stability(
param.def_id,
Some(arg.id()),
arg.span(),
|_, _| {
// Default generic parameters may not be marked
// with stability attributes, i.e. when the
// default parameter was defined at the same time
// as the rest of the type. As such, we ignore missing
// stability attributes.
},
)
}
if let (hir::TyKind::Infer, false) = (&ty.kind, self.allow_ty_infer()) {
inferred_params.push(ty.span);
tcx.ty_error().into()
} else {
self.ast_ty_to_ty(&ty).into()
}
}
(GenericParamDefKind::Const, GenericArg::Const(ct)) => {
ty::Const::from_opt_const_arg_anon_const(
tcx,
ty::WithOptConstParam {
did: tcx.hir().local_def_id(ct.value.hir_id),
const_param_did: Some(param.def_id),
},
)
.into()
}
_ => unreachable!(),
},
// Provide substitutions for parameters for which arguments are inferred.
|substs, param, infer_args| {
match param.kind {
GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
GenericParamDefKind::Type { has_default, .. } => {
if !infer_args && has_default {
// No type parameter provided, but a default exists.
// If we are converting an object type, then the
// `Self` parameter is unknown. However, some of the
// other type parameters may reference `Self` in their
// defaults. This will lead to an ICE if we are not
// careful!
if default_needs_object_self(param) {
missing_type_params.push(param.name.to_string());
tcx.ty_error().into()
} else {
// This is a default type parameter.
self.normalize_ty(
span,
tcx.at(span).type_of(param.def_id).subst_spanned(
tcx,
substs.unwrap(),
Some(span),
),
)
.into()
}
} else if infer_args {
// No type parameters were provided, we can infer all.
let param =
if !default_needs_object_self(param) { Some(param) } else { None };
self.ty_infer(param, span).into()
} else {
// We've already errored above about the mismatch.
tcx.ty_error().into()
}
}
GenericParamDefKind::Const => {
let ty = tcx.at(span).type_of(param.def_id);
// FIXME(const_generics:defaults)
if infer_args {
// No const parameters were provided, we can infer all.
self.ct_infer(ty, Some(param), span).into()
} else {
// We've already errored above about the mismatch.
tcx.const_error(ty).into()
}
}
}
},
);
self.complain_about_missing_type_params(
missing_type_params,
def_id,
span,
generic_args.args.is_empty(),
);
// Convert associated-type bindings or constraints into a separate vector.
// Example: Given this:
//
// T: Iterator<Item = u32>
//
// The `T` is passed in as a self-type; the `Item = u32` is
// not a "type parameter" of the `Iterator` trait, but rather
// a restriction on `<T as Iterator>::Item`, so it is passed
// back separately.
let assoc_bindings = generic_args
.bindings
.iter()
.map(|binding| {
let kind = match binding.kind {
hir::TypeBindingKind::Equality { ref ty } => {
ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
}
hir::TypeBindingKind::Constraint { ref bounds } => {
ConvertedBindingKind::Constraint(bounds)
}
};
ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
})
.collect();
debug!(
"create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
generic_params, self_ty, substs
);
(substs, assoc_bindings, arg_count)
}
crate fn create_substs_for_associated_item(
&self,
tcx: TyCtxt<'tcx>,
span: Span,
item_def_id: DefId,
item_segment: &hir::PathSegment<'_>,
parent_substs: SubstsRef<'tcx>,
) -> SubstsRef<'tcx> {
if tcx.generics_of(item_def_id).params.is_empty() {
self.prohibit_generics(slice::from_ref(item_segment));
parent_substs
} else {
self.create_substs_for_ast_path(
span,
item_def_id,
parent_substs,
item_segment.generic_args(),
item_segment.infer_args,
None,
)
.0
}
}
/// Instantiates the path for the given trait reference, assuming that it's
/// bound to a valid trait type. Returns the `DefId` of the defining trait.
/// The type _cannot_ be a type other than a trait type.
///
/// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
/// are disallowed. Otherwise, they are pushed onto the vector given.
pub fn instantiate_mono_trait_ref(
&self,
trait_ref: &hir::TraitRef<'_>,
self_ty: Ty<'tcx>,
) -> ty::TraitRef<'tcx> {
self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
self.ast_path_to_mono_trait_ref(
trait_ref.path.span,
trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
self_ty,
trait_ref.path.segments.last().unwrap(),
)
}
/// The given trait-ref must actually be a trait.
pub(super) fn instantiate_poly_trait_ref_inner(
&self,
trait_ref: &hir::TraitRef<'_>,
span: Span,
constness: Constness,
self_ty: Ty<'tcx>,
bounds: &mut Bounds<'tcx>,
speculative: bool,
) -> GenericArgCountResult {
let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
let (substs, assoc_bindings, arg_count) = self.create_substs_for_ast_trait_ref(
trait_ref.path.span,
trait_def_id,
self_ty,
trait_ref.path.segments.last().unwrap(),
);
let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
bounds.trait_bounds.push((poly_trait_ref, span, constness));
let mut dup_bindings = FxHashMap::default();
for binding in &assoc_bindings {
// Specify type to assert that error was already reported in `Err` case.
let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
trait_ref.hir_ref_id,
poly_trait_ref,
binding,
bounds,
speculative,
&mut dup_bindings,
binding.span,
);
// Okay to ignore `Err` because of `ErrorReported` (see above).
}
debug!(
"instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
trait_ref, bounds, poly_trait_ref
);
arg_count
}
/// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
/// a full trait reference. The resulting trait reference is returned. This may also generate
/// auxiliary bounds, which are added to `bounds`.
///
/// Example:
///
/// ```
/// poly_trait_ref = Iterator<Item = u32>
/// self_ty = Foo
/// ```
///
/// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
///
/// **A note on binders:** against our usual convention, there is an implied bounder around
/// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
/// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
/// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
/// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
/// however.
pub fn instantiate_poly_trait_ref(
&self,
poly_trait_ref: &hir::PolyTraitRef<'_>,
constness: Constness,
self_ty: Ty<'tcx>,
bounds: &mut Bounds<'tcx>,
) -> GenericArgCountResult {
self.instantiate_poly_trait_ref_inner(
&poly_trait_ref.trait_ref,
poly_trait_ref.span,
constness,
self_ty,
bounds,
false,
)
}
pub fn instantiate_lang_item_trait_ref(
&self,
lang_item: hir::LangItem,
span: Span,
hir_id: hir::HirId,
args: &GenericArgs<'_>,
self_ty: Ty<'tcx>,
bounds: &mut Bounds<'tcx>,
) {
let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
let (substs, assoc_bindings, _) =
self.create_substs_for_ast_path(span, trait_def_id, &[], args, false, Some(self_ty));
let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
bounds.trait_bounds.push((poly_trait_ref, span, Constness::NotConst));
let mut dup_bindings = FxHashMap::default();
for binding in assoc_bindings {
let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
hir_id,
poly_trait_ref,
&binding,
bounds,
false,
&mut dup_bindings,
span,
);
}
}
fn ast_path_to_mono_trait_ref(
&self,
span: Span,
trait_def_id: DefId,
self_ty: Ty<'tcx>,
trait_segment: &hir::PathSegment<'_>,
) -> ty::TraitRef<'tcx> {
let (substs, assoc_bindings, _) =
self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
if let Some(b) = assoc_bindings.first() {
Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
}
ty::TraitRef::new(trait_def_id, substs)
}
fn create_substs_for_ast_trait_ref<'a>(
&self,
span: Span,
trait_def_id: DefId,
self_ty: Ty<'tcx>,
trait_segment: &'a hir::PathSegment<'a>,
) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
self.create_substs_for_ast_path(
span,
trait_def_id,
&[],
trait_segment.generic_args(),
trait_segment.infer_args,
Some(self_ty),
)
}
fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
self.tcx()
.associated_items(trait_def_id)
.find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
.is_some()
}
// Returns `true` if a bounds list includes `?Sized`.
pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
let tcx = self.tcx();
// Try to find an unbound in bounds.
let mut unbound = None;
for ab in ast_bounds {
if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
if unbound.is_none() {
unbound = Some(&ptr.trait_ref);
} else {
tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
}
}
}
let kind_id = tcx.lang_items().require(LangItem::Sized);
match unbound {
Some(tpb) => {
// FIXME(#8559) currently requires the unbound to be built-in.
if let Ok(kind_id) = kind_id {
if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
tcx.sess.span_warn(
span,
"default bound relaxed for a type parameter, but \
this does nothing because the given bound is not \
a default; only `?Sized` is supported",
);
}
}
}
_ if kind_id.is_ok() => {
return false;
}
// No lang item for `Sized`, so we can't add it as a bound.
None => {}
}
true
}
/// This helper takes a *converted* parameter type (`param_ty`)
/// and an *unconverted* list of bounds:
///
/// ```text
/// fn foo<T: Debug>
/// ^ ^^^^^ `ast_bounds` parameter, in HIR form
/// |
/// `param_ty`, in ty form
/// ```
///
/// It adds these `ast_bounds` into the `bounds` structure.
///
/// **A note on binders:** there is an implied binder around
/// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
/// for more details.
fn add_bounds(
&self,
param_ty: Ty<'tcx>,
ast_bounds: &[hir::GenericBound<'_>],
bounds: &mut Bounds<'tcx>,
) {
let mut trait_bounds = Vec::new();
let mut region_bounds = Vec::new();
let constness = self.default_constness_for_trait_bounds();
for ast_bound in ast_bounds {
match *ast_bound {
hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
trait_bounds.push((b, constness))
}
hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
trait_bounds.push((b, Constness::NotConst))
}
hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => self
.instantiate_lang_item_trait_ref(
lang_item, span, hir_id, args, param_ty, bounds,
),
hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
}
}
for (bound, constness) in trait_bounds {
let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
}
bounds.region_bounds.extend(
region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
);
}
/// Translates a list of bounds from the HIR into the `Bounds` data structure.
/// The self-type for the bounds is given by `param_ty`.
///
/// Example:
///
/// ```
/// fn foo<T: Bar + Baz>() { }
/// ^ ^^^^^^^^^ ast_bounds
/// param_ty
/// ```
///
/// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
/// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
/// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
///
/// `span` should be the declaration size of the parameter.
pub fn compute_bounds(
&self,
param_ty: Ty<'tcx>,
ast_bounds: &[hir::GenericBound<'_>],
sized_by_default: SizedByDefault,
span: Span,
) -> Bounds<'tcx> {
let mut bounds = Bounds::default();
self.add_bounds(param_ty, ast_bounds, &mut bounds);
bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
} else {
None
};
bounds
}
/// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
/// onto `bounds`.
///
/// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
/// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
/// the binder (e.g., `&'a u32`) and hence may reference bound regions.
fn add_predicates_for_ast_type_binding(
&self,
hir_ref_id: hir::HirId,
trait_ref: ty::PolyTraitRef<'tcx>,
binding: &ConvertedBinding<'_, 'tcx>,
bounds: &mut Bounds<'tcx>,
speculative: bool,
dup_bindings: &mut FxHashMap<DefId, Span>,
path_span: Span,
) -> Result<(), ErrorReported> {
let tcx = self.tcx();
if !speculative {
// Given something like `U: SomeTrait<T = X>`, we want to produce a
// predicate like `<U as SomeTrait>::T = X`. This is somewhat
// subtle in the event that `T` is defined in a supertrait of
// `SomeTrait`, because in that case we need to upcast.
//
// That is, consider this case:
//
// ```
// trait SubTrait: SuperTrait<i32> { }
// trait SuperTrait<A> { type T; }
//
// ... B: SubTrait<T = foo> ...
// ```
//
// We want to produce `<B as SuperTrait<i32>>::T == foo`.
// Find any late-bound regions declared in `ty` that are not
// declared in the trait-ref. These are not well-formed.
//
// Example:
//
// for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
// for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
if let ConvertedBindingKind::Equality(ty) = binding.kind {
let late_bound_in_trait_ref =
tcx.collect_constrained_late_bound_regions(&trait_ref);
let late_bound_in_ty =
tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
// FIXME: point at the type params that don't have appropriate lifetimes:
// struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
// ---- ---- ^^^^^^^
self.validate_late_bound_regions(
late_bound_in_trait_ref,
late_bound_in_ty,
|br_name| {
struct_span_err!(
tcx.sess,
binding.span,
E0582,
"binding for associated type `{}` references {}, \
which does not appear in the trait input types",
binding.item_name,
br_name
)
},
);
}
}
let candidate =
if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
// Simple case: X is defined in the current trait.
trait_ref
} else {
// Otherwise, we have to walk through the supertraits to find
// those that do.
self.one_bound_for_assoc_type(
|| traits::supertraits(tcx, trait_ref),
|| trait_ref.print_only_trait_path().to_string(),
binding.item_name,
path_span,
|| match binding.kind {
ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
_ => None,
},
)?
};
let (assoc_ident, def_scope) =
tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
// We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
// of calling `filter_by_name_and_kind`.
let assoc_ty = tcx
.associated_items(candidate.def_id())
.filter_by_name_unhygienic(assoc_ident.name)
.find(|i| {
i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
})
.expect("missing associated type");
if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
tcx.sess
.struct_span_err(
binding.span,
&format!("associated type `{}` is private", binding.item_name),
)
.span_label(binding.span, "private associated type")
.emit();
}
tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
if !speculative {
dup_bindings
.entry(assoc_ty.def_id)
.and_modify(|prev_span| {
self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
span: binding.span,
prev_span: *prev_span,
item_name: binding.item_name,
def_path: tcx.def_path_str(assoc_ty.container.id()),
});
})
.or_insert(binding.span);
}
match binding.kind {
ConvertedBindingKind::Equality(ref ty) => {
// "Desugar" a constraint like `T: Iterator<Item = u32>` this to
// the "projection predicate" for:
//
// `<T as Iterator>::Item = u32`
bounds.projection_bounds.push((
candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
projection_ty: ty::ProjectionTy::from_ref_and_name(
tcx,
trait_ref,
binding.item_name,
),
ty,
}),
binding.span,
));
}
ConvertedBindingKind::Constraint(ast_bounds) => {
// "Desugar" a constraint like `T: Iterator<Item: Debug>` to
//
// `<T as Iterator>::Item: Debug`
//
// Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
// parameter to have a skipped binder.
let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
self.add_bounds(param_ty, ast_bounds, bounds);
}
}
Ok(())
}
fn ast_path_to_ty(
&self,
span: Span,
did: DefId,
item_segment: &hir::PathSegment<'_>,
) -> Ty<'tcx> {
let substs = self.ast_path_substs_for_ty(span, did, item_segment);
self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
}
fn conv_object_ty_poly_trait_ref(
&self,
span: Span,
trait_bounds: &[hir::PolyTraitRef<'_>],
lifetime: &hir::Lifetime,
borrowed: bool,
) -> Ty<'tcx> {
let tcx = self.tcx();
let mut bounds = Bounds::default();
let mut potential_assoc_types = Vec::new();
let dummy_self = self.tcx().types.trait_object_dummy_self;
for trait_bound in trait_bounds.iter().rev() {
if let GenericArgCountResult {
correct:
Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
..
} = self.instantiate_poly_trait_ref(
trait_bound,
Constness::NotConst,
dummy_self,
&mut bounds,
) {
potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
}
}
// Expand trait aliases recursively and check that only one regular (non-auto) trait
// is used and no 'maybe' bounds are used.
let expanded_traits =
traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
if regular_traits.len() > 1 {
let first_trait = &regular_traits[0];
let additional_trait = &regular_traits[1];
let mut err = struct_span_err!(
tcx.sess,
additional_trait.bottom().1,
E0225,
"only auto traits can be used as additional traits in a trait object"
);
additional_trait.label_with_exp_info(
&mut err,
"additional non-auto trait",
"additional use",
);
first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
err.help(&format!(
"consider creating a new trait with all of these as super-traits and using that \
trait here instead: `trait NewTrait: {} {{}}`",
regular_traits
.iter()
.map(|t| t.trait_ref().print_only_trait_path().to_string())
.collect::<Vec<_>>()
.join(" + "),
));
err.note(
"auto-traits like `Send` and `Sync` are traits that have special properties; \
for more information on them, visit \
<https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
);
err.emit();
}
if regular_traits.is_empty() && auto_traits.is_empty() {
tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span });
return tcx.ty_error();
}
// Check that there are no gross object safety violations;
// most importantly, that the supertraits don't contain `Self`,
// to avoid ICEs.
for item in &regular_traits {
let object_safety_violations =
astconv_object_safety_violations(tcx, item.trait_ref().def_id());
if !object_safety_violations.is_empty() {
report_object_safety_error(
tcx,
span,
item.trait_ref().def_id(),
&object_safety_violations[..],
)
.emit();
return tcx.ty_error();
}
}
// Use a `BTreeSet` to keep output in a more consistent order.
let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
let regular_traits_refs_spans = bounds
.trait_bounds
.into_iter()
.filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
for (base_trait_ref, span, constness) in regular_traits_refs_spans {
assert_eq!(constness, Constness::NotConst);
for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
debug!(
"conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
obligation.predicate
);
match obligation.predicate.skip_binders() {
ty::PredicateAtom::Trait(pred, _) => {
let pred = ty::Binder::bind(pred);
associated_types.entry(span).or_default().extend(
tcx.associated_items(pred.def_id())
.in_definition_order()
.filter(|item| item.kind == ty::AssocKind::Type)
.map(|item| item.def_id),
);
}
ty::PredicateAtom::Projection(pred) => {
let pred = ty::Binder::bind(pred);
// A `Self` within the original bound will be substituted with a
// `trait_object_dummy_self`, so check for that.
let references_self =
pred.skip_binder().ty.walk().any(|arg| arg == dummy_self.into());
// If the projection output contains `Self`, force the user to
// elaborate it explicitly to avoid a lot of complexity.
//
// The "classicaly useful" case is the following:
// ```
// trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
// type MyOutput;
// }
// ```
//
// Here, the user could theoretically write `dyn MyTrait<Output = X>`,
// but actually supporting that would "expand" to an infinitely-long type
// `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
//
// Instead, we force the user to write
// `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
// the discussion in #56288 for alternatives.
if !references_self {
// Include projections defined on supertraits.
bounds.projection_bounds.push((pred, span));
}
}
_ => (),
}
}
}
for (projection_bound, _) in &bounds.projection_bounds {
for def_ids in associated_types.values_mut() {
def_ids.remove(&projection_bound.projection_def_id());
}
}
self.complain_about_missing_associated_types(
associated_types,
potential_assoc_types,
trait_bounds,
);
// De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
// `dyn Trait + Send`.
auto_traits.sort_by_key(|i| i.trait_ref().def_id());
auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
debug!("regular_traits: {:?}", regular_traits);
debug!("auto_traits: {:?}", auto_traits);
// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
// removing the dummy `Self` type (`trait_object_dummy_self`).
let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
if trait_ref.self_ty() != dummy_self {
// FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
// which picks up non-supertraits where clauses - but also, the object safety
// completely ignores trait aliases, which could be object safety hazards. We
// `delay_span_bug` here to avoid an ICE in stable even when the feature is
// disabled. (#66420)
tcx.sess.delay_span_bug(
DUMMY_SP,
&format!(
"trait_ref_to_existential called on {:?} with non-dummy Self",
trait_ref,
),
);
}
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
};
// Erase the `dummy_self` (`trait_object_dummy_self`) used above.
let existential_trait_refs =
regular_traits.iter().map(|i| i.trait_ref().map_bound(trait_ref_to_existential));
let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
bound.map_bound(|b| {
let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
ty::ExistentialProjection {
ty: b.ty,
item_def_id: b.projection_ty.item_def_id,
substs: trait_ref.substs,
}
})
});
// Calling `skip_binder` is okay because the predicates are re-bound.
let regular_trait_predicates = existential_trait_refs
.map(|trait_ref| ty::ExistentialPredicate::Trait(trait_ref.skip_binder()));
let auto_trait_predicates = auto_traits
.into_iter()
.map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
let mut v = regular_trait_predicates
.chain(auto_trait_predicates)
.chain(
existential_projections
.map(|x| ty::ExistentialPredicate::Projection(x.skip_binder())),
)
.collect::<SmallVec<[_; 8]>>();
v.sort_by(|a, b| a.stable_cmp(tcx, b));
v.dedup();
let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
// Use explicitly-specified region bound.
let region_bound = if !lifetime.is_elided() {
self.ast_region_to_region(lifetime, None)
} else {
self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
if tcx.named_region(lifetime.hir_id).is_some() {
self.ast_region_to_region(lifetime, None)
} else {
self.re_infer(None, span).unwrap_or_else(|| {
let mut err = struct_span_err!(
tcx.sess,
span,
E0228,
"the lifetime bound for this object type cannot be deduced \
from context; please supply an explicit bound"
);
if borrowed {
// We will have already emitted an error E0106 complaining about a
// missing named lifetime in `&dyn Trait`, so we elide this one.
err.delay_as_bug();
} else {
err.emit();
}
tcx.lifetimes.re_static
})
}
})
};
debug!("region_bound: {:?}", region_bound);
let ty = tcx.mk_dynamic(existential_predicates, region_bound);
debug!("trait_object_type: {:?}", ty);
ty
}
fn report_ambiguous_associated_type(
&self,
span: Span,
type_str: &str,
trait_str: &str,
name: Symbol,
) {
let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
if let (Some(_), Ok(snippet)) = (
self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
self.tcx().sess.source_map().span_to_snippet(span),
) {
err.span_suggestion(
span,
"you are looking for the module in `std`, not the primitive type",
format!("std::{}", snippet),
Applicability::MachineApplicable,
);
} else {
err.span_suggestion(
span,
"use fully-qualified syntax",
format!("<{} as {}>::{}", type_str, trait_str, name),
Applicability::HasPlaceholders,
);
}
err.emit();
}
// Search for a bound on a type parameter which includes the associated item
// given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
// This function will fail if there are no suitable bounds or there is
// any ambiguity.
fn find_bound_for_assoc_item(
&self,
ty_param_def_id: LocalDefId,
assoc_name: Ident,
span: Span,
) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
let tcx = self.tcx();
debug!(
"find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
ty_param_def_id, assoc_name, span,
);
let predicates =
&self.get_type_parameter_bounds(span, ty_param_def_id.to_def_id()).predicates;
debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
let param_name = tcx.hir().ty_param_name(param_hir_id);
self.one_bound_for_assoc_type(
|| {
traits::transitive_bounds(
tcx,
predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
)
},
|| param_name.to_string(),
assoc_name,
span,
|| None,
)
}
// Checks that `bounds` contains exactly one element and reports appropriate
// errors otherwise.
fn one_bound_for_assoc_type<I>(
&self,
all_candidates: impl Fn() -> I,
ty_param_name: impl Fn() -> String,
assoc_name: Ident,
span: Span,
is_equality: impl Fn() -> Option<String>,
) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
where
I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
{
let mut matching_candidates = all_candidates()
.filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
let bound = match matching_candidates.next() {
Some(bound) => bound,
None => {
self.complain_about_assoc_type_not_found(
all_candidates,
&ty_param_name(),
assoc_name,
span,
);
return Err(ErrorReported);
}
};
debug!("one_bound_for_assoc_type: bound = {:?}", bound);
if let Some(bound2) = matching_candidates.next() {
debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
let is_equality = is_equality();
let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
let mut err = if is_equality.is_some() {
// More specific Error Index entry.
struct_span_err!(
self.tcx().sess,
span,
E0222,
"ambiguous associated type `{}` in bounds of `{}`",
assoc_name,
ty_param_name()
)
} else {
struct_span_err!(
self.tcx().sess,
span,
E0221,
"ambiguous associated type `{}` in bounds of `{}`",
assoc_name,
ty_param_name()
)
};
err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
let mut where_bounds = vec![];
for bound in bounds {
let bound_id = bound.def_id();
let bound_span = self
.tcx()
.associated_items(bound_id)
.find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
.and_then(|item| self.tcx().hir().span_if_local(item.def_id));
if let Some(bound_span) = bound_span {
err.span_label(
bound_span,
format!(
"ambiguous `{}` from `{}`",
assoc_name,
bound.print_only_trait_path(),
),
);
if let Some(constraint) = &is_equality {
where_bounds.push(format!(
" T: {trait}::{assoc} = {constraint}",
trait=bound.print_only_trait_path(),
assoc=assoc_name,
constraint=constraint,
));
} else {
err.span_suggestion(
span,
"use fully qualified syntax to disambiguate",
format!(
"<{} as {}>::{}",
ty_param_name(),
bound.print_only_trait_path(),
assoc_name,
),
Applicability::MaybeIncorrect,
);
}
} else {
err.note(&format!(
"associated type `{}` could derive from `{}`",
ty_param_name(),
bound.print_only_trait_path(),
));
}
}
if !where_bounds.is_empty() {
err.help(&format!(
"consider introducing a new type parameter `T` and adding `where` constraints:\
\n where\n T: {},\n{}",
ty_param_name(),
where_bounds.join(",\n"),
));
}
err.emit();
if !where_bounds.is_empty() {
return Err(ErrorReported);
}
}
Ok(bound)
}
// Create a type from a path to an associated type.
// For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
// and item_segment is the path segment for `D`. We return a type and a def for
// the whole path.
// Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
// parameter or `Self`.
pub fn associated_path_to_ty(
&self,
hir_ref_id: hir::HirId,
span: Span,
qself_ty: Ty<'tcx>,
qself_res: Res,
assoc_segment: &hir::PathSegment<'_>,
permit_variants: bool,
) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
let tcx = self.tcx();
let assoc_ident = assoc_segment.ident;
debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
// Check if we have an enum variant.
let mut variant_resolution = None;
if let ty::Adt(adt_def, _) = qself_ty.kind() {
if adt_def.is_enum() {
let variant_def = adt_def
.variants
.iter()
.find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
if let Some(variant_def) = variant_def {
if permit_variants {
tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
self.prohibit_generics(slice::from_ref(assoc_segment));
return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
} else {
variant_resolution = Some(variant_def.def_id);
}
}
}
}
// Find the type of the associated item, and the trait where the associated
// item is declared.
let bound = match (&qself_ty.kind(), qself_res) {
(_, Res::SelfTy(Some(_), Some((impl_def_id, _)))) => {
// `Self` in an impl of a trait -- we have a concrete self type and a
// trait reference.
let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
Some(trait_ref) => trait_ref,
None => {
// A cycle error occurred, most likely.
return Err(ErrorReported);
}
};
self.one_bound_for_assoc_type(
|| traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
|| "Self".to_string(),
assoc_ident,
span,
|| None,
)?
}
(
&ty::Param(_),
Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
_ => {
if variant_resolution.is_some() {
// Variant in type position
let msg = format!("expected type, found variant `{}`", assoc_ident);
tcx.sess.span_err(span, &msg);
} else if qself_ty.is_enum() {
let mut err = struct_span_err!(
tcx.sess,
assoc_ident.span,
E0599,
"no variant named `{}` found for enum `{}`",
assoc_ident,
qself_ty,
);
let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
if let Some(suggested_name) = find_best_match_for_name(
adt_def.variants.iter().map(|variant| &variant.ident.name),
assoc_ident.name,
None,
) {
err.span_suggestion(
assoc_ident.span,
"there is a variant with a similar name",
suggested_name.to_string(),
Applicability::MaybeIncorrect,
);
} else {
err.span_label(
assoc_ident.span,
format!("variant not found in `{}`", qself_ty),
);
}
if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
let sp = tcx.sess.source_map().guess_head_span(sp);
err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
}
err.emit();
} else if !qself_ty.references_error() {
// Don't print `TyErr` to the user.
self.report_ambiguous_associated_type(
span,
&qself_ty.to_string(),
"Trait",
assoc_ident.name,
);
}
return Err(ErrorReported);
}
};
let trait_did = bound.def_id();
let (assoc_ident, def_scope) =
tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
// We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
// of calling `filter_by_name_and_kind`.
let item = tcx
.associated_items(trait_did)
.in_definition_order()
.find(|i| {
i.kind.namespace() == Namespace::TypeNS
&& i.ident.normalize_to_macros_2_0() == assoc_ident
})
.expect("missing associated type");
let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
let ty = self.normalize_ty(span, ty);
let kind = DefKind::AssocTy;
if !item.vis.is_accessible_from(def_scope, tcx) {
let kind = kind.descr(item.def_id);
let msg = format!("{} `{}` is private", kind, assoc_ident);
tcx.sess
.struct_span_err(span, &msg)
.span_label(span, &format!("private {}", kind))
.emit();
}
tcx.check_stability(item.def_id, Some(hir_ref_id), span);
if let Some(variant_def_id) = variant_resolution {
tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
let mut err = lint.build("ambiguous associated item");
let mut could_refer_to = |kind: DefKind, def_id, also| {
let note_msg = format!(
"`{}` could{} refer to the {} defined here",
assoc_ident,
also,
kind.descr(def_id)
);
err.span_note(tcx.def_span(def_id), &note_msg);
};
could_refer_to(DefKind::Variant, variant_def_id, "");
could_refer_to(kind, item.def_id, " also");
err.span_suggestion(
span,
"use fully-qualified syntax",
format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
Applicability::MachineApplicable,
);
err.emit();
});
}
Ok((ty, kind, item.def_id))
}
fn qpath_to_ty(
&self,
span: Span,
opt_self_ty: Option<Ty<'tcx>>,
item_def_id: DefId,
trait_segment: &hir::PathSegment<'_>,
item_segment: &hir::PathSegment<'_>,
) -> Ty<'tcx> {
let tcx = self.tcx();
let trait_def_id = tcx.parent(item_def_id).unwrap();
debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
let self_ty = if let Some(ty) = opt_self_ty {
ty
} else {
let path_str = tcx.def_path_str(trait_def_id);
let def_id = self.item_def_id();
debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
let parent_def_id = def_id
.and_then(|def_id| {
def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
})
.map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
// If the trait in segment is the same as the trait defining the item,
// use the `<Self as ..>` syntax in the error.
let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
"Self"
} else {
"Type"
};
self.report_ambiguous_associated_type(
span,
type_name,
&path_str,
item_segment.ident.name,
);
return tcx.ty_error();
};
debug!("qpath_to_ty: self_type={:?}", self_ty);
let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
let item_substs = self.create_substs_for_associated_item(
tcx,
span,
item_def_id,
item_segment,
trait_ref.substs,
);
debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
}
pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
&self,
segments: T,
) -> bool {
let mut has_err = false;
for segment in segments {
let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
for arg in segment.generic_args().args {
let (span, kind) = match arg {
hir::GenericArg::Lifetime(lt) => {
if err_for_lt {
continue;
}
err_for_lt = true;
has_err = true;
(lt.span, "lifetime")
}
hir::GenericArg::Type(ty) => {
if err_for_ty {
continue;
}
err_for_ty = true;
has_err = true;
(ty.span, "type")
}
hir::GenericArg::Const(ct) => {
if err_for_ct {
continue;
}
err_for_ct = true;
has_err = true;
(ct.span, "const")
}
};
let mut err = struct_span_err!(
self.tcx().sess,
span,
E0109,
"{} arguments are not allowed for this type",
kind,
);
err.span_label(span, format!("{} argument not allowed", kind));
err.emit();
if err_for_lt && err_for_ty && err_for_ct {
break;
}
}
// Only emit the first error to avoid overloading the user with error messages.
if let [binding, ..] = segment.generic_args().bindings {
has_err = true;
Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
}
}
has_err
}
// FIXME(eddyb, varkor) handle type paths here too, not just value ones.
pub fn def_ids_for_value_path_segments(
&self,
segments: &[hir::PathSegment<'_>],
self_ty: Option<Ty<'tcx>>,
kind: DefKind,
def_id: DefId,
) -> Vec<PathSeg> {
// We need to extract the type parameters supplied by the user in
// the path `path`. Due to the current setup, this is a bit of a
// tricky-process; the problem is that resolve only tells us the
// end-point of the path resolution, and not the intermediate steps.
// Luckily, we can (at least for now) deduce the intermediate steps
// just from the end-point.
//
// There are basically five cases to consider:
//
// 1. Reference to a constructor of a struct:
//
// struct Foo<T>(...)
//
// In this case, the parameters are declared in the type space.
//
// 2. Reference to a constructor of an enum variant:
//
// enum E<T> { Foo(...) }
//
// In this case, the parameters are defined in the type space,
// but may be specified either on the type or the variant.
//
// 3. Reference to a fn item or a free constant:
//
// fn foo<T>() { }
//
// In this case, the path will again always have the form
// `a::b::foo::<T>` where only the final segment should have
// type parameters. However, in this case, those parameters are
// declared on a value, and hence are in the `FnSpace`.
//
// 4. Reference to a method or an associated constant:
//
// impl<A> SomeStruct<A> {
// fn foo<B>(...)
// }
//
// Here we can have a path like
// `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
// may appear in two places. The penultimate segment,
// `SomeStruct::<A>`, contains parameters in TypeSpace, and the
// final segment, `foo::<B>` contains parameters in fn space.
//
// The first step then is to categorize the segments appropriately.
let tcx = self.tcx();
assert!(!segments.is_empty());
let last = segments.len() - 1;
let mut path_segs = vec![];
match kind {
// Case 1. Reference to a struct constructor.
DefKind::Ctor(CtorOf::Struct, ..) => {
// Everything but the final segment should have no
// parameters at all.
let generics = tcx.generics_of(def_id);
// Variant and struct constructors use the
// generics of their parent type definition.
let generics_def_id = generics.parent.unwrap_or(def_id);
path_segs.push(PathSeg(generics_def_id, last));
}
// Case 2. Reference to a variant constructor.
DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
let (generics_def_id, index) = if let Some(adt_def) = adt_def {
debug_assert!(adt_def.is_enum());
(adt_def.did, last)
} else if last >= 1 && segments[last - 1].args.is_some() {
// Everything but the penultimate segment should have no
// parameters at all.
let mut def_id = def_id;
// `DefKind::Ctor` -> `DefKind::Variant`
if let DefKind::Ctor(..) = kind {
def_id = tcx.parent(def_id).unwrap()
}
// `DefKind::Variant` -> `DefKind::Enum`
let enum_def_id = tcx.parent(def_id).unwrap();
(enum_def_id, last - 1)
} else {
// FIXME: lint here recommending `Enum::<...>::Variant` form
// instead of `Enum::Variant::<...>` form.
// Everything but the final segment should have no
// parameters at all.
let generics = tcx.generics_of(def_id);
// Variant and struct constructors use the
// generics of their parent type definition.
(generics.parent.unwrap_or(def_id), last)
};
path_segs.push(PathSeg(generics_def_id, index));
}
// Case 3. Reference to a top-level value.
DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
path_segs.push(PathSeg(def_id, last));
}
// Case 4. Reference to a method or associated const.
DefKind::AssocFn | DefKind::AssocConst => {
if segments.len() >= 2 {
let generics = tcx.generics_of(def_id);
path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
}
path_segs.push(PathSeg(def_id, last));
}
kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
}
debug!("path_segs = {:?}", path_segs);
path_segs
}
// Check a type `Path` and convert it to a `Ty`.
pub fn res_to_ty(
&self,
opt_self_ty: Option<Ty<'tcx>>,
path: &hir::Path<'_>,
permit_variants: bool,
) -> Ty<'tcx> {
let tcx = self.tcx();
debug!(
"res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
path.res, opt_self_ty, path.segments
);
let span = path.span;
match path.res {
Res::Def(DefKind::OpaqueTy, did) => {
// Check for desugared `impl Trait`.
assert!(ty::is_impl_trait_defn(tcx, did).is_none());
let item_segment = path.segments.split_last().unwrap();
self.prohibit_generics(item_segment.1);
let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
self.normalize_ty(span, tcx.mk_opaque(did, substs))
}
Res::Def(
DefKind::Enum
| DefKind::TyAlias
| DefKind::Struct
| DefKind::Union
| DefKind::ForeignTy,
did,
) => {
assert_eq!(opt_self_ty, None);
self.prohibit_generics(path.segments.split_last().unwrap().1);
self.ast_path_to_ty(span, did, path.segments.last().unwrap())
}
Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
// Convert "variant type" as if it were a real type.
// The resulting `Ty` is type of the variant's enum for now.
assert_eq!(opt_self_ty, None);
let path_segs =
self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
let generic_segs: FxHashSet<_> =
path_segs.iter().map(|PathSeg(_, index)| index).collect();
self.prohibit_generics(path.segments.iter().enumerate().filter_map(
|(index, seg)| {
if !generic_segs.contains(&index) { Some(seg) } else { None }
},
));
let PathSeg(def_id, index) = path_segs.last().unwrap();
self.ast_path_to_ty(span, *def_id, &path.segments[*index])
}
Res::Def(DefKind::TyParam, def_id) => {
assert_eq!(opt_self_ty, None);
self.prohibit_generics(path.segments);
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
let item_id = tcx.hir().get_parent_node(hir_id);
let item_def_id = tcx.hir().local_def_id(item_id);
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&def_id];
tcx.mk_ty_param(index, tcx.hir().name(hir_id))
}
Res::SelfTy(Some(_), None) => {
// `Self` in trait or type alias.
assert_eq!(opt_self_ty, None);
self.prohibit_generics(path.segments);
tcx.types.self_param
}
Res::SelfTy(_, Some((def_id, forbid_generic))) => {
// `Self` in impl (we know the concrete type).
assert_eq!(opt_self_ty, None);
self.prohibit_generics(path.segments);
// Try to evaluate any array length constants.
let normalized_ty = self.normalize_ty(span, tcx.at(span).type_of(def_id));
if forbid_generic && normalized_ty.needs_subst() {
let mut err = tcx.sess.struct_span_err(
path.span,
"generic `Self` types are currently not permitted in anonymous constants",
);
if let Some(hir::Node::Item(&hir::Item {
kind: hir::ItemKind::Impl { self_ty, .. },
..
})) = tcx.hir().get_if_local(def_id)
{
err.span_note(self_ty.span, "not a concrete type");
}
err.emit();
tcx.ty_error()
} else {
normalized_ty
}
}
Res::Def(DefKind::AssocTy, def_id) => {
debug_assert!(path.segments.len() >= 2);
self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
self.qpath_to_ty(
span,
opt_self_ty,
def_id,
&path.segments[path.segments.len() - 2],
path.segments.last().unwrap(),
)
}
Res::PrimTy(prim_ty) => {
assert_eq!(opt_self_ty, None);
self.prohibit_generics(path.segments);
match prim_ty {
hir::PrimTy::Bool => tcx.types.bool,
hir::PrimTy::Char => tcx.types.char,
hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
hir::PrimTy::Str => tcx.types.str_,
}
}
Res::Err => {
self.set_tainted_by_errors();
self.tcx().ty_error()
}
_ => span_bug!(span, "unexpected resolution: {:?}", path.res),
}
}
/// Parses the programmer's textual representation of a type into our
/// internal notion of a type.
pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
self.ast_ty_to_ty_inner(ast_ty, false)
}
/// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
/// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
let tcx = self.tcx();
let result_ty = match ast_ty.kind {
hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
hir::TyKind::Ptr(ref mt) => {
tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
}
hir::TyKind::Rptr(ref region, ref mt) => {
let r = self.ast_region_to_region(region, None);
debug!("ast_ty_to_ty: r={:?}", r);
let t = self.ast_ty_to_ty_inner(&mt.ty, true);
tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
}
hir::TyKind::Never => tcx.types.never,
hir::TyKind::Tup(ref fields) => {
tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
}
hir::TyKind::BareFn(ref bf) => {
require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
tcx.mk_fn_ptr(self.ty_of_fn(
bf.unsafety,
bf.abi,
&bf.decl,
&hir::Generics::empty(),
None,
))
}
hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
}
hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
self.res_to_ty(opt_self_ty, path, false)
}
hir::TyKind::OpaqueDef(item_id, ref lifetimes) => {
let opaque_ty = tcx.hir().expect_item(item_id.id);
let def_id = tcx.hir().local_def_id(item_id.id).to_def_id();
match opaque_ty.kind {
hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
self.impl_trait_ty_to_ty(def_id, lifetimes, impl_trait_fn.is_some())
}
ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
}
}
hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
let ty = self.ast_ty_to_ty(qself);
let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
path.res
} else {
Res::Err
};
self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
.map(|(ty, _, _)| ty)
.unwrap_or_else(|_| tcx.ty_error())
}
hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
let def_id = tcx.require_lang_item(lang_item, Some(span));
let (substs, _, _) = self.create_substs_for_ast_path(
span,
def_id,
&[],
&GenericArgs::none(),
true,
None,
);
self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
}
hir::TyKind::Array(ref ty, ref length) => {
let length_def_id = tcx.hir().local_def_id(length.hir_id);
let length = ty::Const::from_anon_const(tcx, length_def_id);
let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
self.normalize_ty(ast_ty.span, array_ty)
}
hir::TyKind::Typeof(ref _e) => {
tcx.sess.emit_err(TypeofReservedKeywordUsed { span: ast_ty.span });
tcx.ty_error()
}
hir::TyKind::Infer => {
// Infer also appears as the type of arguments or return
// values in a ExprKind::Closure, or as
// the type of local variables. Both of these cases are
// handled specially and will not descend into this routine.
self.ty_infer(None, ast_ty.span)
}
hir::TyKind::Err => tcx.ty_error(),
};
debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
result_ty
}
pub fn impl_trait_ty_to_ty(
&self,
def_id: DefId,
lifetimes: &[hir::GenericArg<'_>],
replace_parent_lifetimes: bool,
) -> Ty<'tcx> {
debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
let tcx = self.tcx();
let generics = tcx.generics_of(def_id);
debug!("impl_trait_ty_to_ty: generics={:?}", generics);
let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
// Our own parameters are the resolved lifetimes.
match param.kind {
GenericParamDefKind::Lifetime => {
if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
self.ast_region_to_region(lifetime, None).into()
} else {
bug!()
}
}
_ => bug!(),
}
} else {
match param.kind {
// For RPIT (return position impl trait), only lifetimes
// mentioned in the impl Trait predicate are captured by
// the opaque type, so the lifetime parameters from the
// parent item need to be replaced with `'static`.
//
// For `impl Trait` in the types of statics, constants,
// locals and type aliases. These capture all parent
// lifetimes, so they can use their identity subst.
GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
tcx.lifetimes.re_static.into()
}
_ => tcx.mk_param_from_def(param),
}
}
});
debug!("impl_trait_ty_to_ty: substs={:?}", substs);
let ty = tcx.mk_opaque(def_id, substs);
debug!("impl_trait_ty_to_ty: {}", ty);
ty
}
pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
match ty.kind {
hir::TyKind::Infer if expected_ty.is_some() => {
self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
expected_ty.unwrap()
}
_ => self.ast_ty_to_ty(ty),
}
}
pub fn ty_of_fn(
&self,
unsafety: hir::Unsafety,
abi: abi::Abi,
decl: &hir::FnDecl<'_>,
generics: &hir::Generics<'_>,
ident_span: Option<Span>,
) -> ty::PolyFnSig<'tcx> {
debug!("ty_of_fn");
let tcx = self.tcx();
// We proactively collect all the inferred type params to emit a single error per fn def.
let mut visitor = PlaceholderHirTyCollector::default();
for ty in decl.inputs {
visitor.visit_ty(ty);
}
walk_generics(&mut visitor, generics);
let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
let output_ty = match decl.output {
hir::FnRetTy::Return(ref output) => {
visitor.visit_ty(output);
self.ast_ty_to_ty(output)
}
hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
};
debug!("ty_of_fn: output_ty={:?}", output_ty);
let bare_fn_ty =
ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
if !self.allow_ty_infer() {
// We always collect the spans for placeholder types when evaluating `fn`s, but we
// only want to emit an error complaining about them if infer types (`_`) are not
// allowed. `allow_ty_infer` gates this behavior. We check for the presence of
// `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
crate::collect::placeholder_type_error(
tcx,
ident_span.map(|sp| sp.shrink_to_hi()),
&generics.params[..],
visitor.0,
true,
);
}
// Find any late-bound regions declared in return type that do
// not appear in the arguments. These are not well-formed.
//
// Example:
// for<'a> fn() -> &'a str <-- 'a is bad
// for<'a> fn(&'a String) -> &'a str <-- 'a is ok
let inputs = bare_fn_ty.inputs();
let late_bound_in_args =
tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
let output = bare_fn_ty.output();
let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
struct_span_err!(
tcx.sess,
decl.output.span(),
E0581,
"return type references {}, which is not constrained by the fn input types",
br_name
)
});
bare_fn_ty
}
fn validate_late_bound_regions(
&self,
constrained_regions: FxHashSet<ty::BoundRegion>,
referenced_regions: FxHashSet<ty::BoundRegion>,
generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
) {
for br in referenced_regions.difference(&constrained_regions) {
let br_name = match *br {
ty::BrNamed(_, name) => format!("lifetime `{}`", name),
ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
};
let mut err = generate_err(&br_name);
if let ty::BrAnon(_) = *br {
// The only way for an anonymous lifetime to wind up
// in the return type but **also** be unconstrained is
// if it only appears in "associated types" in the
// input. See #47511 and #62200 for examples. In this case,
// though we can easily give a hint that ought to be
// relevant.
err.note(
"lifetimes appearing in an associated type are not considered constrained",
);
}
err.emit();
}
}
/// Given the bounds on an object, determines what single region bound (if any) we can
/// use to summarize this type. The basic idea is that we will use the bound the user
/// provided, if they provided one, and otherwise search the supertypes of trait bounds
/// for region bounds. It may be that we can derive no bound at all, in which case
/// we return `None`.
fn compute_object_lifetime_bound(
&self,
span: Span,
existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
) -> Option<ty::Region<'tcx>> // if None, use the default
{
let tcx = self.tcx();
debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
// No explicit region bound specified. Therefore, examine trait
// bounds and see if we can derive region bounds from those.
let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
// If there are no derived region bounds, then report back that we
// can find no region bound. The caller will use the default.
if derived_region_bounds.is_empty() {
return None;
}
// If any of the derived region bounds are 'static, that is always
// the best choice.
if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
return Some(tcx.lifetimes.re_static);
}
// Determine whether there is exactly one unique region in the set
// of derived region bounds. If so, use that. Otherwise, report an
// error.
let r = derived_region_bounds[0];
if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
tcx.sess.emit_err(AmbiguousLifetimeBound { span });
}
Some(r)
}
}