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fuchsia / third_party / rust / c38f75c21f016bffbf841ed5abce338f94201bde / . / compiler / rustc_hir_analysis / src / hir_ty_lowering / mod.rs
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//! HIR ty lowering: Lowers type-system entities[^1] from the [HIR][hir] to
//! the [`rustc_middle::ty`] representation.
//!
//! Not to be confused with *AST lowering* which lowers AST constructs to HIR ones
//! or with *THIR* / *MIR* *lowering* / *building* which lowers HIR *bodies*
//! (i.e., “executable code”) to THIR / MIR.
//!
//! Most lowering routines are defined on [`dyn HirTyLowerer`](HirTyLowerer) directly,
//! like the main routine of this module, `lower_ty`.
//!
//! This module used to be called `astconv`.
//!
//! [^1]: This includes types, lifetimes / regions, constants in type positions,
//! trait references and bounds.
mod bounds;
pub mod errors;
pub mod generics;
mod lint;
mod object_safety;
use crate::bounds::Bounds;
use crate::collect::HirPlaceholderCollector;
use crate::errors::{AmbiguousLifetimeBound, WildPatTy};
use crate::hir_ty_lowering::errors::{prohibit_assoc_item_binding, GenericsArgsErrExtend};
use crate::hir_ty_lowering::generics::{check_generic_arg_count, lower_generic_args};
use crate::middle::resolve_bound_vars as rbv;
use crate::require_c_abi_if_c_variadic;
use rustc_ast::TraitObjectSyntax;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
use rustc_errors::{
codes::*, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, 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::{GenericArg, GenericArgs, HirId};
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::ObligationCause;
use rustc_middle::middle::stability::AllowUnstable;
use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
use rustc_middle::ty::{
self, Const, GenericArgKind, GenericArgsRef, GenericParamDefKind, ParamEnv, Ty, TyCtxt,
TypeVisitableExt,
};
use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
use rustc_span::edit_distance::find_best_match_for_name;
use rustc_span::symbol::{kw, Ident, Symbol};
use rustc_span::{sym, Span, DUMMY_SP};
use rustc_target::spec::abi;
use rustc_trait_selection::traits::wf::object_region_bounds;
use rustc_trait_selection::traits::{self, ObligationCtxt};
use std::fmt::Display;
use std::slice;
/// A path segment that is semantically allowed to have generic arguments.
#[derive(Debug)]
pub struct GenericPathSegment(pub DefId, pub usize);
#[derive(Copy, Clone, Debug)]
pub struct OnlySelfBounds(pub bool);
#[derive(Copy, Clone, Debug)]
pub enum PredicateFilter {
/// All predicates may be implied by the trait.
All,
/// Only traits that reference `Self: ..` are implied by the trait.
SelfOnly,
/// Only traits that reference `Self: ..` and define an associated type
/// with the given ident are implied by the trait.
SelfThatDefines(Ident),
/// Only traits that reference `Self: ..` and their associated type bounds.
/// For example, given `Self: Tr<A: B>`, this would expand to `Self: Tr`
/// and `<Self as Tr>::A: B`.
SelfAndAssociatedTypeBounds,
}
/// A context which can lower type-system entities from the [HIR][hir] to
/// the [`rustc_middle::ty`] representation.
///
/// This trait used to be called `AstConv`.
pub trait HirTyLowerer<'tcx> {
fn tcx(&self) -> TyCtxt<'tcx>;
/// Returns the [`DefId`] of the overarching item whose constituents get lowered.
fn item_def_id(&self) -> DefId;
/// Returns `true` if the current context allows the use of inference variables.
fn allow_infer(&self) -> bool;
/// Returns the region 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 the const to use when a const is omitted.
fn ct_infer(
&self,
ty: Ty<'tcx>,
param: Option<&ty::GenericParamDef>,
span: Span,
) -> Const<'tcx>;
/// Probe bounds in scope where the bounded type coincides with the given type parameter.
///
/// Rephrased, this returns bounds of the form `T: Trait`, where `T` is a type parameter
/// with the given `def_id`. This is a subset of the full set of bounds.
///
/// This method may use the given `assoc_name` to disregard bounds whose trait reference
/// doesn't define an associated item with the provided name.
///
/// This is used for one specific purpose: Resolving “short-hand” associated type references
/// like `T::Item` where `T` is a type parameter. 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 probe_ty_param_bounds(
&self,
span: Span,
def_id: LocalDefId,
assoc_name: Ident,
) -> ty::GenericPredicates<'tcx>;
/// Lower an associated type to a projection.
///
/// This method has to be defined by the concrete lowering context because
/// dealing with higher-ranked trait references depends on its capabilities:
///
/// If the context can make use of type inference, it can simply instantiate
/// any late-bound vars bound by the trait reference with inference variables.
/// If it doesn't support type inference, there is nothing reasonable it can
/// do except reject the associated type.
///
/// The canonical example of this is associated type `T::P` where `T` is a type
/// param constrained by `T: for<'a> Trait<'a>` and where `Trait` defines `P`.
fn lower_assoc_ty(
&self,
span: Span,
item_def_id: DefId,
item_segment: &hir::PathSegment<'tcx>,
poly_trait_ref: ty::PolyTraitRef<'tcx>,
) -> Ty<'tcx>;
/// Returns `AdtDef` if `ty` is an ADT.
///
/// Note that `ty` might be a alias type that needs normalization.
/// This used to get the enum variants in scope of the type.
/// For example, `Self::A` could refer to an associated type
/// or to an enum variant depending on the result of this function.
fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>>;
/// Record the lowered type of a HIR node in this context.
fn record_ty(&self, hir_id: HirId, ty: Ty<'tcx>, span: Span);
/// The inference context of the lowering context if applicable.
fn infcx(&self) -> Option<&InferCtxt<'tcx>>;
/// Taint the context with errors.
///
/// Invoke this when you encounter an error from some prior pass like name resolution.
/// This is used to help suppress derived errors typeck might otherwise report.
fn set_tainted_by_errors(&self, e: ErrorGuaranteed);
/// Convenience method for coercing the lowering context into a trait object type.
///
/// Most lowering routines are defined on the trait object type directly
/// necessitating a coercion step from the concrete lowering context.
fn lowerer(&self) -> &dyn HirTyLowerer<'tcx>
where
Self: Sized,
{
self
}
}
/// 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, Debug)]
pub enum ExplicitLateBound {
Yes,
No,
}
#[derive(Copy, Clone, PartialEq)]
pub enum IsMethodCall {
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, Debug)]
pub struct GenericArgCountMismatch {
/// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
pub reported: Option<ErrorGuaranteed>,
/// 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, Debug)]
pub struct GenericArgCountResult {
pub explicit_late_bound: ExplicitLateBound,
pub correct: Result<(), GenericArgCountMismatch>,
}
/// A context which can lower HIR's [`GenericArg`] to `rustc_middle`'s [`ty::GenericArg`].
///
/// Its only consumer is [`generics::lower_generic_args`].
/// Read its documentation to learn more.
pub trait GenericArgsLowerer<'a, 'tcx> {
fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'tcx>>, bool);
fn provided_kind(
&mut self,
param: &ty::GenericParamDef,
arg: &GenericArg<'tcx>,
) -> ty::GenericArg<'tcx>;
fn inferred_kind(
&mut self,
args: Option<&[ty::GenericArg<'tcx>]>,
param: &ty::GenericParamDef,
infer_args: bool,
) -> ty::GenericArg<'tcx>;
}
impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
/// Lower a lifetime from the HIR to our internal notion of a lifetime called a *region*.
#[instrument(level = "debug", skip(self), ret)]
pub fn lower_lifetime(
&self,
lifetime: &hir::Lifetime,
def: Option<&ty::GenericParamDef>,
) -> ty::Region<'tcx> {
let tcx = self.tcx();
let lifetime_name = |def_id| tcx.hir().name(tcx.local_def_id_to_hir_id(def_id));
match tcx.named_bound_var(lifetime.hir_id) {
Some(rbv::ResolvedArg::StaticLifetime) => tcx.lifetimes.re_static,
Some(rbv::ResolvedArg::LateBound(debruijn, index, def_id)) => {
let name = lifetime_name(def_id.expect_local());
let br = ty::BoundRegion {
var: ty::BoundVar::from_u32(index),
kind: ty::BrNamed(def_id, name),
};
ty::Region::new_bound(tcx, debruijn, br)
}
Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
let name = tcx.hir().ty_param_name(def_id.expect_local());
let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&def_id];
ty::Region::new_early_param(tcx, ty::EarlyParamRegion { def_id, index, name })
}
Some(rbv::ResolvedArg::Free(scope, id)) => {
let name = lifetime_name(id.expect_local());
ty::Region::new_late_param(tcx, scope, ty::BrNamed(id, name))
// (*) -- not late-bound, won't change
}
Some(rbv::ResolvedArg::Error(guar)) => ty::Region::new_error(tcx, guar),
None => {
self.re_infer(def, lifetime.ident.span).unwrap_or_else(|| {
debug!(?lifetime, "unelided lifetime in signature");
// This indicates an illegal lifetime
// elision. `resolve_lifetime` should have
// reported an error in this case -- but if
// not, let's error out.
ty::Region::new_error_with_message(
tcx,
lifetime.ident.span,
"unelided lifetime in signature",
)
})
}
}
}
pub fn lower_generic_args_of_path_segment(
&self,
span: Span,
def_id: DefId,
item_segment: &hir::PathSegment<'tcx>,
) -> GenericArgsRef<'tcx> {
let (args, _) = self.lower_generic_args_of_path(
span,
def_id,
&[],
item_segment,
None,
ty::BoundConstness::NotConst,
);
if let Some(b) = item_segment.args().bindings.first() {
prohibit_assoc_item_binding(self.tcx(), b, Some((def_id, item_segment, span)));
}
args
}
/// Lower the generic arguments provided to some path.
///
/// If this is a trait reference, you also need to pass the self type `self_ty`.
/// The lowering process may involve applying defaulted type parameters.
///
/// Associated item bindings are not handled here!
///
/// ### Example
///
/// ```ignore (illustrative)
/// 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 `GenericArgsRef`
/// 4. Associated type bindings like `Output = u32` are contained in `generic_args.bindings`.
///
/// Note that the type listing given here is *exactly* what the user provided.
///
/// For (generic) associated types
///
/// ```ignore (illustrative)
/// <Vec<u8> as Iterable<u8>>::Iter::<'a>
/// ```
///
/// We have the parent args are the args for the parent trait:
/// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
/// type itself: `['a]`. The returned `GenericArgsRef` concatenates these two
/// lists: `[Vec<u8>, u8, 'a]`.
#[instrument(level = "debug", skip(self, span), ret)]
fn lower_generic_args_of_path(
&self,
span: Span,
def_id: DefId,
parent_args: &[ty::GenericArg<'tcx>],
segment: &hir::PathSegment<'tcx>,
self_ty: Option<Ty<'tcx>>,
constness: ty::BoundConstness,
) -> (GenericArgsRef<'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).
let tcx = self.tcx();
let generics = tcx.generics_of(def_id);
debug!(?generics);
if generics.has_self {
if generics.parent.is_some() {
// The parent is a trait so it should have at least one
// generic parameter for the `Self` type.
assert!(!parent_args.is_empty())
} else {
// This item (presumably a trait) needs a self-type.
assert!(self_ty.is_some());
}
} else {
assert!(self_ty.is_none());
}
let mut arg_count = check_generic_arg_count(
tcx,
def_id,
segment,
generics,
GenericArgPosition::Type,
self_ty.is_some(),
);
if let Err(err) = &arg_count.correct
&& let Some(reported) = err.reported
{
self.set_tainted_by_errors(reported);
}
// Skip processing if type has no generic parameters.
// Traits always have `Self` as a generic parameter, which means they will not return early
// here and so associated type bindings will be handled regardless of whether there are any
// non-`Self` generic parameters.
if generics.params.is_empty() {
return (tcx.mk_args(parent_args), arg_count);
}
struct GenericArgsCtxt<'a, 'tcx> {
lowerer: &'a dyn HirTyLowerer<'tcx>,
def_id: DefId,
generic_args: &'a GenericArgs<'tcx>,
span: Span,
inferred_params: Vec<Span>,
infer_args: bool,
}
impl<'a, 'tcx> GenericArgsLowerer<'a, 'tcx> for GenericArgsCtxt<'a, 'tcx> {
fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'tcx>>, bool) {
if did == self.def_id {
(Some(self.generic_args), self.infer_args)
} else {
// The last component of this tuple is unimportant.
(None, false)
}
}
fn provided_kind(
&mut self,
param: &ty::GenericParamDef,
arg: &GenericArg<'tcx>,
) -> ty::GenericArg<'tcx> {
let tcx = self.lowerer.tcx();
let mut handle_ty_args = |has_default, ty: &hir::Ty<'tcx>| {
if has_default {
tcx.check_optional_stability(
param.def_id,
Some(arg.hir_id()),
arg.span(),
None,
AllowUnstable::No,
|_, _| {
// 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.lowerer.allow_infer()) {
self.inferred_params.push(ty.span);
Ty::new_misc_error(tcx).into()
} else {
self.lowerer.lower_ty(ty).into()
}
};
match (&param.kind, arg) {
(GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
self.lowerer.lower_lifetime(lt, Some(param)).into()
}
(&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
handle_ty_args(has_default, ty)
}
(&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
handle_ty_args(has_default, &inf.to_ty())
}
(GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
let did = ct.value.def_id;
tcx.feed_anon_const_type(did, tcx.type_of(param.def_id));
ty::Const::from_anon_const(tcx, did).into()
}
(&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
let ty = tcx
.at(self.span)
.type_of(param.def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic");
if self.lowerer.allow_infer() {
self.lowerer.ct_infer(ty, Some(param), inf.span).into()
} else {
self.inferred_params.push(inf.span);
ty::Const::new_misc_error(tcx, ty).into()
}
}
(kind, arg) => span_bug!(
self.span,
"mismatched path argument for kind {kind:?}: found arg {arg:?}"
),
}
}
fn inferred_kind(
&mut self,
args: Option<&[ty::GenericArg<'tcx>]>,
param: &ty::GenericParamDef,
infer_args: bool,
) -> ty::GenericArg<'tcx> {
let tcx = self.lowerer.tcx();
match param.kind {
GenericParamDefKind::Lifetime => self
.lowerer
.re_infer(Some(param), self.span)
.unwrap_or_else(|| {
debug!(?param, "unelided lifetime in signature");
// This indicates an illegal lifetime in a non-assoc-trait position
ty::Region::new_error_with_message(
tcx,
self.span,
"unelided lifetime in signature",
)
})
.into(),
GenericParamDefKind::Type { has_default, .. } => {
if !infer_args && has_default {
// No type parameter provided, but a default exists.
let args = args.unwrap();
if args.iter().any(|arg| match arg.unpack() {
GenericArgKind::Type(ty) => ty.references_error(),
_ => false,
}) {
// Avoid ICE #86756 when type error recovery goes awry.
return Ty::new_misc_error(tcx).into();
}
tcx.at(self.span).type_of(param.def_id).instantiate(tcx, args).into()
} else if infer_args {
self.lowerer.ty_infer(Some(param), self.span).into()
} else {
// We've already errored above about the mismatch.
Ty::new_misc_error(tcx).into()
}
}
GenericParamDefKind::Const { has_default, .. } => {
let ty = tcx
.at(self.span)
.type_of(param.def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic");
if let Err(guar) = ty.error_reported() {
return ty::Const::new_error(tcx, guar, ty).into();
}
// FIXME(effects) see if we should special case effect params here
if !infer_args && has_default {
tcx.const_param_default(param.def_id)
.instantiate(tcx, args.unwrap())
.into()
} else {
if infer_args {
self.lowerer.ct_infer(ty, Some(param), self.span).into()
} else {
// We've already errored above about the mismatch.
ty::Const::new_misc_error(tcx, ty).into()
}
}
}
}
}
}
let mut args_ctx = GenericArgsCtxt {
lowerer: self,
def_id,
span,
generic_args: segment.args(),
inferred_params: vec![],
infer_args: segment.infer_args,
};
if let ty::BoundConstness::Const | ty::BoundConstness::ConstIfConst = constness
&& generics.has_self
&& !tcx.has_attr(def_id, sym::const_trait)
{
let e = tcx.dcx().emit_err(crate::errors::ConstBoundForNonConstTrait {
span,
modifier: constness.as_str(),
});
self.set_tainted_by_errors(e);
arg_count.correct =
Err(GenericArgCountMismatch { reported: Some(e), invalid_args: vec![] });
}
let args = lower_generic_args(
tcx,
def_id,
parent_args,
self_ty.is_some(),
self_ty,
&arg_count,
&mut args_ctx,
);
(args, arg_count)
}
#[instrument(level = "debug", skip_all)]
pub fn lower_generic_args_of_assoc_item(
&self,
span: Span,
item_def_id: DefId,
item_segment: &hir::PathSegment<'tcx>,
parent_args: GenericArgsRef<'tcx>,
) -> GenericArgsRef<'tcx> {
debug!(?span, ?item_def_id, ?item_segment);
let (args, _) = self.lower_generic_args_of_path(
span,
item_def_id,
parent_args,
item_segment,
None,
ty::BoundConstness::NotConst,
);
if let Some(b) = item_segment.args().bindings.first() {
prohibit_assoc_item_binding(self.tcx(), b, Some((item_def_id, item_segment, span)));
}
args
}
/// Lower a trait reference as found in an impl header as the implementee.
///
/// The self type `self_ty` is the implementer of the trait.
pub fn lower_impl_trait_ref(
&self,
trait_ref: &hir::TraitRef<'tcx>,
self_ty: Ty<'tcx>,
) -> ty::TraitRef<'tcx> {
let _ = self.prohibit_generic_args(
trait_ref.path.segments.split_last().unwrap().1.iter(),
GenericsArgsErrExtend::None,
);
self.lower_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(),
true,
ty::BoundConstness::NotConst,
)
}
/// Lower a polymorphic trait reference given a self type into `bounds`.
///
/// *Polymorphic* in the sense that it may bind late-bound vars.
///
/// This may generate auxiliary bounds if the trait reference contains associated item bindings.
///
/// ### Example
///
/// Given the trait ref `Iterator<Item = u32>` and the self type `Ty`, this will add the
///
/// 1. *trait predicate* `<Ty as Iterator>` (known as `Foo: Iterator` in surface syntax) and the
/// 2. *projection predicate* `<Ty as Iterator>::Item = u32`
///
/// to `bounds`.
///
/// ### A Note on Binders
///
/// Against our usual convention, there is an implied binder around the `self_ty` and the
/// `trait_ref` here. So they may reference late-bound vars.
///
/// 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 `trait_ref` would be `Bar<'a>`.
/// The lowered poly-trait-ref will track this binder explicitly, however.
#[instrument(level = "debug", skip(self, span, constness, bounds))]
pub(crate) fn lower_poly_trait_ref(
&self,
trait_ref: &hir::TraitRef<'tcx>,
span: Span,
constness: ty::BoundConstness,
polarity: ty::PredicatePolarity,
self_ty: Ty<'tcx>,
bounds: &mut Bounds<'tcx>,
only_self_bounds: OnlySelfBounds,
) -> GenericArgCountResult {
let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
let trait_segment = trait_ref.path.segments.last().unwrap();
let _ = self.prohibit_generic_args(
trait_ref.path.segments.split_last().unwrap().1.iter(),
GenericsArgsErrExtend::None,
);
self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
let (generic_args, arg_count) = self.lower_generic_args_of_path(
trait_ref.path.span,
trait_def_id,
&[],
trait_segment,
Some(self_ty),
constness,
);
let tcx = self.tcx();
let bound_vars = tcx.late_bound_vars(trait_ref.hir_ref_id);
debug!(?bound_vars);
let poly_trait_ref = ty::Binder::bind_with_vars(
ty::TraitRef::new(tcx, trait_def_id, generic_args),
bound_vars,
);
debug!(?poly_trait_ref);
bounds.push_trait_bound(tcx, poly_trait_ref, span, polarity);
let mut dup_bindings = FxIndexMap::default();
for binding in trait_segment.args().bindings {
// Don't register additional associated type bounds for negative bounds,
// since we should have emitten an error for them earlier, and they will
// not be well-formed!
if polarity != ty::PredicatePolarity::Positive {
assert!(
self.tcx().dcx().has_errors().is_some(),
"negative trait bounds should not have bindings",
);
continue;
}
// Specify type to assert that error was already reported in `Err` case.
let _: Result<_, ErrorGuaranteed> = self.lower_assoc_item_binding(
trait_ref.hir_ref_id,
poly_trait_ref,
binding,
bounds,
&mut dup_bindings,
binding.span,
only_self_bounds,
);
// Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
}
arg_count
}
/// Lower a monomorphic trait reference given a self type while prohibiting associated item bindings.
///
/// *Monomorphic* in the sense that it doesn't bind any late-bound vars.
fn lower_mono_trait_ref(
&self,
span: Span,
trait_def_id: DefId,
self_ty: Ty<'tcx>,
trait_segment: &hir::PathSegment<'tcx>,
is_impl: bool,
// FIXME(effects): Move all host param things in HIR ty lowering to AST lowering.
constness: ty::BoundConstness,
) -> ty::TraitRef<'tcx> {
self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
let (generic_args, _) = self.lower_generic_args_of_path(
span,
trait_def_id,
&[],
trait_segment,
Some(self_ty),
constness,
);
if let Some(b) = trait_segment.args().bindings.first() {
prohibit_assoc_item_binding(self.tcx(), b, Some((trait_def_id, trait_segment, span)));
}
ty::TraitRef::new(self.tcx(), trait_def_id, generic_args)
}
fn probe_trait_that_defines_assoc_item(
&self,
trait_def_id: DefId,
assoc_kind: ty::AssocKind,
assoc_name: Ident,
) -> bool {
self.tcx()
.associated_items(trait_def_id)
.find_by_name_and_kind(self.tcx(), assoc_name, assoc_kind, trait_def_id)
.is_some()
}
fn lower_path_segment(
&self,
span: Span,
did: DefId,
item_segment: &hir::PathSegment<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx();
let args = self.lower_generic_args_of_path_segment(span, did, item_segment);
if let DefKind::TyAlias = tcx.def_kind(did)
&& tcx.type_alias_is_lazy(did)
{
// Type aliases defined in crates that have the
// feature `lazy_type_alias` enabled get encoded as a type alias that normalization will
// then actually instantiate the where bounds of.
let alias_ty = ty::AliasTy::new(tcx, did, args);
Ty::new_alias(tcx, ty::Weak, alias_ty)
} else {
tcx.at(span).type_of(did).instantiate(tcx, args)
}
}
/// Search for a trait bound on a type parameter whose trait defines the associated type given by `assoc_name`.
///
/// This fails if there is no such bound in the list of candidates or if there are multiple
/// candidates in which case it reports ambiguity.
///
/// `ty_param_def_id` is the `LocalDefId` of the type parameter.
#[instrument(level = "debug", skip_all, ret)]
fn probe_single_ty_param_bound_for_assoc_ty(
&self,
ty_param_def_id: LocalDefId,
assoc_name: Ident,
span: Span,
) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
debug!(?ty_param_def_id, ?assoc_name, ?span);
let tcx = self.tcx();
let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_name).predicates;
debug!("predicates={:#?}", predicates);
let param_name = tcx.hir().ty_param_name(ty_param_def_id);
self.probe_single_bound_for_assoc_item(
|| {
traits::transitive_bounds_that_define_assoc_item(
tcx,
predicates
.iter()
.filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref))),
assoc_name,
)
},
param_name,
Some(ty_param_def_id),
ty::AssocKind::Type,
assoc_name,
span,
None,
)
}
/// Search for a single trait bound whose trait defines the associated item given by `assoc_name`.
///
/// This fails if there is no such bound in the list of candidates or if there are multiple
/// candidates in which case it reports ambiguity.
#[instrument(level = "debug", skip(self, all_candidates, ty_param_name, binding), ret)]
fn probe_single_bound_for_assoc_item<I>(
&self,
all_candidates: impl Fn() -> I,
ty_param_name: impl Display,
ty_param_def_id: Option<LocalDefId>,
assoc_kind: ty::AssocKind,
assoc_name: Ident,
span: Span,
binding: Option<&hir::TypeBinding<'tcx>>,
) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
where
I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
{
let tcx = self.tcx();
let mut matching_candidates = all_candidates().filter(|r| {
self.probe_trait_that_defines_assoc_item(r.def_id(), assoc_kind, assoc_name)
});
let Some(bound) = matching_candidates.next() else {
let reported = self.complain_about_assoc_item_not_found(
all_candidates,
&ty_param_name.to_string(),
ty_param_def_id,
assoc_kind,
assoc_name,
span,
binding,
);
self.set_tainted_by_errors(reported);
return Err(reported);
};
debug!(?bound);
if let Some(bound2) = matching_candidates.next() {
debug!(?bound2);
let assoc_kind_str = assoc_kind_str(assoc_kind);
let ty_param_name = &ty_param_name.to_string();
let mut err = tcx.dcx().create_err(crate::errors::AmbiguousAssocItem {
span,
assoc_kind: assoc_kind_str,
assoc_name,
ty_param_name,
});
// Provide a more specific error code index entry for equality bindings.
err.code(
if let Some(binding) = binding
&& let hir::TypeBindingKind::Equality { .. } = binding.kind
{
E0222
} else {
E0221
},
);
// FIXME(#97583): Resugar equality bounds to type/const bindings.
// FIXME: Turn this into a structured, translateable & more actionable suggestion.
let mut where_bounds = vec![];
for bound in [bound, bound2].into_iter().chain(matching_candidates) {
let bound_id = bound.def_id();
let bound_span = tcx
.associated_items(bound_id)
.find_by_name_and_kind(tcx, assoc_name, assoc_kind, bound_id)
.and_then(|item| tcx.hir().span_if_local(item.def_id));
if let Some(bound_span) = bound_span {
err.span_label(
bound_span,
format!("ambiguous `{assoc_name}` from `{}`", bound.print_trait_sugared(),),
);
if let Some(binding) = binding {
match binding.kind {
hir::TypeBindingKind::Equality { term } => {
let term: ty::Term<'_> = match term {
hir::Term::Ty(ty) => self.lower_ty(ty).into(),
hir::Term::Const(ct) => {
ty::Const::from_anon_const(tcx, ct.def_id).into()
}
};
// FIXME(#97583): This isn't syntactically well-formed!
where_bounds.push(format!(
" T: {trait}::{assoc_name} = {term}",
trait = bound.print_only_trait_path(),
));
}
// FIXME: Provide a suggestion.
hir::TypeBindingKind::Constraint { bounds: _ } => {}
}
} else {
err.span_suggestion_verbose(
span.with_hi(assoc_name.span.lo()),
"use fully-qualified syntax to disambiguate",
format!("<{ty_param_name} as {}>::", bound.print_only_trait_path()),
Applicability::MaybeIncorrect,
);
}
} else {
err.note(format!(
"associated {assoc_kind_str} `{assoc_name}` could derive from `{}`",
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: {ty_param_name},\n{}",
where_bounds.join(",\n"),
));
}
let reported = err.emit();
self.set_tainted_by_errors(reported);
if !where_bounds.is_empty() {
return Err(reported);
}
}
Ok(bound)
}
/// Lower a [type-relative] path referring to an associated type or to an enum variant.
///
/// If the path refers to an enum variant and `permit_variants` holds,
/// the returned type is simply the provided self type `qself_ty`.
///
/// A path like `A::B::C::D` is understood as `<A::B::C>::D`. I.e.,
/// `qself_ty` / `qself` is `A::B::C` and `assoc_segment` is `D`.
/// We return the lowered type and the `DefId` for the whole path.
///
/// We only support associated type paths whose self type is a type parameter or a `Self`
/// type alias (in a trait impl) like `T::Ty` (where `T` is a ty param) or `Self::Ty`.
/// We **don't** support paths whose self type is an arbitrary type like `Struct::Ty` where
/// struct `Struct` impls an in-scope trait that defines an associated type called `Ty`.
/// For the latter case, we report ambiguity.
/// While desirable to support, the implemention would be non-trivial. Tracked in [#22519].
///
/// At the time of writing, *inherent associated types* are also resolved here. This however
/// is [problematic][iat]. A proper implementation would be as non-trivial as the one
/// described in the previous paragraph and their modeling of projections would likely be
/// very similar in nature.
///
/// [type-relative]: hir::QPath::TypeRelative
/// [#22519]: https://github.com/rust-lang/rust/issues/22519
/// [iat]: https://github.com/rust-lang/rust/issues/8995#issuecomment-1569208403
//
// NOTE: When this function starts resolving `Trait::AssocTy` successfully
// it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
#[instrument(level = "debug", skip_all, ret)]
pub fn lower_assoc_path(
&self,
hir_ref_id: HirId,
span: Span,
qself_ty: Ty<'tcx>,
qself: &'tcx hir::Ty<'tcx>,
assoc_segment: &'tcx hir::PathSegment<'tcx>,
permit_variants: bool,
) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
debug!(%qself_ty, ?assoc_segment.ident);
let tcx = self.tcx();
let assoc_ident = assoc_segment.ident;
let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = &qself.kind {
path.res
} else {
Res::Err
};
// Check if we have an enum variant or an inherent associated type.
let mut variant_resolution = None;
if let Some(adt_def) = self.probe_adt(span, qself_ty) {
if adt_def.is_enum() {
let variant_def = adt_def
.variants()
.iter()
.find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), 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, None);
let _ = self.prohibit_generic_args(
slice::from_ref(assoc_segment).iter(),
GenericsArgsErrExtend::EnumVariant { qself, assoc_segment, adt_def },
);
return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
} else {
variant_resolution = Some(variant_def.def_id);
}
}
}
// FIXME(inherent_associated_types, #106719): Support self types other than ADTs.
if let Some((ty, did)) = self.probe_inherent_assoc_ty(
assoc_ident,
assoc_segment,
adt_def.did(),
qself_ty,
hir_ref_id,
span,
)? {
return Ok((ty, DefKind::AssocTy, did));
}
}
// 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::SelfTyAlias { alias_to: impl_def_id, is_trait_impl: true, .. }) => {
// `Self` in an impl of a trait -- we have a concrete self type and a
// trait reference.
let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
// A cycle error occurred, most likely.
tcx.dcx().span_bug(span, "expected cycle error");
};
self.probe_single_bound_for_assoc_item(
|| {
traits::supertraits(
tcx,
ty::Binder::dummy(trait_ref.instantiate_identity()),
)
},
kw::SelfUpper,
None,
ty::AssocKind::Type,
assoc_ident,
span,
None,
)?
}
(
&ty::Param(_),
Res::SelfTyParam { trait_: param_did } | Res::Def(DefKind::TyParam, param_did),
) => self.probe_single_ty_param_bound_for_assoc_ty(
param_did.expect_local(),
assoc_ident,
span,
)?,
_ => {
let reported = if variant_resolution.is_some() {
// Variant in type position
let msg = format!("expected type, found variant `{assoc_ident}`");
tcx.dcx().span_err(span, msg)
} else if qself_ty.is_enum() {
let mut err = struct_span_code_err!(
tcx.dcx(),
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.name)
.collect::<Vec<Symbol>>(),
assoc_ident.name,
None,
) {
err.span_suggestion(
assoc_ident.span,
"there is a variant with a similar name",
suggested_name,
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()) {
err.span_label(sp, format!("variant `{assoc_ident}` not found here"));
}
err.emit()
} else if let Err(reported) = qself_ty.error_reported() {
reported
} else if let ty::Alias(ty::Opaque, alias_ty) = qself_ty.kind() {
// `<impl Trait as OtherTrait>::Assoc` makes no sense.
struct_span_code_err!(
tcx.dcx(),
tcx.def_span(alias_ty.def_id),
E0667,
"`impl Trait` is not allowed in path parameters"
)
.emit() // Already reported in an earlier stage.
} else {
self.maybe_report_similar_assoc_fn(span, qself_ty, qself)?;
let traits: Vec<_> =
self.probe_traits_that_match_assoc_ty(qself_ty, assoc_ident);
// Don't print `ty::Error` to the user.
self.report_ambiguous_assoc_ty(
span,
&[qself_ty.to_string()],
&traits,
assoc_ident.name,
)
};
self.set_tainted_by_errors(reported);
return Err(reported);
}
};
let trait_did = bound.def_id();
let assoc_ty_did = self.probe_assoc_ty(assoc_ident, hir_ref_id, span, trait_did).unwrap();
let ty = self.lower_assoc_ty(span, assoc_ty_did, assoc_segment, bound);
if let Some(variant_def_id) = variant_resolution {
tcx.node_span_lint(
AMBIGUOUS_ASSOCIATED_ITEMS,
hir_ref_id,
span,
"ambiguous associated item",
|lint| {
let mut could_refer_to = |kind: DefKind, def_id, also| {
let note_msg = format!(
"`{}` could{} refer to the {} defined here",
assoc_ident,
also,
tcx.def_kind_descr(kind, def_id)
);
lint.span_note(tcx.def_span(def_id), note_msg);
};
could_refer_to(DefKind::Variant, variant_def_id, "");
could_refer_to(DefKind::AssocTy, assoc_ty_did, " also");
lint.span_suggestion(
span,
"use fully-qualified syntax",
format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
Applicability::MachineApplicable,
);
},
);
}
Ok((ty, DefKind::AssocTy, assoc_ty_did))
}
fn probe_inherent_assoc_ty(
&self,
name: Ident,
segment: &hir::PathSegment<'tcx>,
adt_did: DefId,
self_ty: Ty<'tcx>,
block: HirId,
span: Span,
) -> Result<Option<(Ty<'tcx>, DefId)>, ErrorGuaranteed> {
let tcx = self.tcx();
// Don't attempt to look up inherent associated types when the feature is not enabled.
// Theoretically it'd be fine to do so since we feature-gate their definition site.
// However, due to current limitations of the implementation (caused by us performing
// selection during HIR ty lowering instead of in the trait solver), IATs can lead to cycle
// errors (#108491) which mask the feature-gate error, needlessly confusing users
// who use IATs by accident (#113265).
if !tcx.features().inherent_associated_types {
return Ok(None);
}
let candidates: Vec<_> = tcx
.inherent_impls(adt_did)?
.iter()
.filter_map(|&impl_| Some((impl_, self.probe_assoc_ty_unchecked(name, block, impl_)?)))
.collect();
if candidates.is_empty() {
return Ok(None);
}
//
// Select applicable inherent associated type candidates modulo regions.
//
// In contexts that have no inference context, just make a new one.
// We do need a local variable to store it, though.
let infcx_;
let infcx = match self.infcx() {
Some(infcx) => infcx,
None => {
assert!(!self_ty.has_infer());
infcx_ = tcx.infer_ctxt().ignoring_regions().build();
&infcx_
}
};
// FIXME(inherent_associated_types): Acquiring the ParamEnv this early leads to cycle errors
// when inside of an ADT (#108491) or where clause.
let param_env = tcx.param_env(block.owner);
let mut universes = if self_ty.has_escaping_bound_vars() {
vec![None; self_ty.outer_exclusive_binder().as_usize()]
} else {
vec![]
};
let (impl_, (assoc_item, def_scope)) = crate::traits::with_replaced_escaping_bound_vars(
infcx,
&mut universes,
self_ty,
|self_ty| {
self.select_inherent_assoc_type_candidates(
infcx, name, span, self_ty, param_env, candidates,
)
},
)?;
self.check_assoc_ty(assoc_item, name, def_scope, block, span);
// FIXME(fmease): Currently creating throwaway `parent_args` to please
// `lower_generic_args_of_assoc_item`. Modify the latter instead (or sth. similar) to
// not require the parent args logic.
let parent_args = ty::GenericArgs::identity_for_item(tcx, impl_);
let args = self.lower_generic_args_of_assoc_item(span, assoc_item, segment, parent_args);
let args = tcx.mk_args_from_iter(
std::iter::once(ty::GenericArg::from(self_ty))
.chain(args.into_iter().skip(parent_args.len())),
);
let ty = Ty::new_alias(tcx, ty::Inherent, ty::AliasTy::new(tcx, assoc_item, args));
Ok(Some((ty, assoc_item)))
}
fn select_inherent_assoc_type_candidates(
&self,
infcx: &InferCtxt<'tcx>,
name: Ident,
span: Span,
self_ty: Ty<'tcx>,
param_env: ParamEnv<'tcx>,
candidates: Vec<(DefId, (DefId, DefId))>,
) -> Result<(DefId, (DefId, DefId)), ErrorGuaranteed> {
let tcx = self.tcx();
let mut fulfillment_errors = Vec::new();
let applicable_candidates: Vec<_> = candidates
.iter()
.copied()
.filter(|&(impl_, _)| {
infcx.probe(|_| {
let ocx = ObligationCtxt::new(infcx);
let self_ty = ocx.normalize(&ObligationCause::dummy(), param_env, self_ty);
let impl_args = infcx.fresh_args_for_item(span, impl_);
let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args);
let impl_ty = ocx.normalize(&ObligationCause::dummy(), param_env, impl_ty);
// Check that the self types can be related.
if ocx.eq(&ObligationCause::dummy(), param_env, impl_ty, self_ty).is_err() {
return false;
}
// Check whether the impl imposes obligations we have to worry about.
let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args);
let impl_bounds =
ocx.normalize(&ObligationCause::dummy(), param_env, impl_bounds);
let impl_obligations = traits::predicates_for_generics(
|_, _| ObligationCause::dummy(),
param_env,
impl_bounds,
);
ocx.register_obligations(impl_obligations);
let mut errors = ocx.select_where_possible();
if !errors.is_empty() {
fulfillment_errors.append(&mut errors);
return false;
}
true
})
})
.collect();
match &applicable_candidates[..] {
&[] => Err(self.complain_about_inherent_assoc_ty_not_found(
name,
self_ty,
candidates,
fulfillment_errors,
span,
)),
&[applicable_candidate] => Ok(applicable_candidate),
&[_, ..] => Err(self.complain_about_ambiguous_inherent_assoc_ty(
name,
applicable_candidates.into_iter().map(|(_, (candidate, _))| candidate).collect(),
span,
)),
}
}
fn probe_assoc_ty(&self, name: Ident, block: HirId, span: Span, scope: DefId) -> Option<DefId> {
let (item, def_scope) = self.probe_assoc_ty_unchecked(name, block, scope)?;
self.check_assoc_ty(item, name, def_scope, block, span);
Some(item)
}
fn probe_assoc_ty_unchecked(
&self,
name: Ident,
block: HirId,
scope: DefId,
) -> Option<(DefId, DefId)> {
let tcx = self.tcx();
let (ident, def_scope) = tcx.adjust_ident_and_get_scope(name, scope, block);
// We have already adjusted the item name above, so compare with `.normalize_to_macros_2_0()`
// instead of calling `filter_by_name_and_kind` which would needlessly normalize the
// `ident` again and again.
let item = tcx.associated_items(scope).in_definition_order().find(|i| {
i.kind.namespace() == Namespace::TypeNS
&& i.ident(tcx).normalize_to_macros_2_0() == ident
})?;
Some((item.def_id, def_scope))
}
fn check_assoc_ty(&self, item: DefId, name: Ident, def_scope: DefId, block: HirId, span: Span) {
let tcx = self.tcx();
let kind = DefKind::AssocTy;
if !tcx.visibility(item).is_accessible_from(def_scope, tcx) {
let kind = tcx.def_kind_descr(kind, item);
let msg = format!("{kind} `{name}` is private");
let def_span = tcx.def_span(item);
let reported = tcx
.dcx()
.struct_span_err(span, msg)
.with_code(E0624)
.with_span_label(span, format!("private {kind}"))
.with_span_label(def_span, format!("{kind} defined here"))
.emit();
self.set_tainted_by_errors(reported);
}
tcx.check_stability(item, Some(block), span, None);
}
fn probe_traits_that_match_assoc_ty(
&self,
qself_ty: Ty<'tcx>,
assoc_ident: Ident,
) -> Vec<String> {
let tcx = self.tcx();
// In contexts that have no inference context, just make a new one.
// We do need a local variable to store it, though.
let infcx_;
let infcx = if let Some(infcx) = self.infcx() {
infcx
} else {
assert!(!qself_ty.has_infer());
infcx_ = tcx.infer_ctxt().build();
&infcx_
};
tcx.all_traits()
.filter(|trait_def_id| {
// Consider only traits with the associated type
tcx.associated_items(*trait_def_id)
.in_definition_order()
.any(|i| {
i.kind.namespace() == Namespace::TypeNS
&& i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
&& matches!(i.kind, ty::AssocKind::Type)
})
// Consider only accessible traits
&& tcx.visibility(*trait_def_id)
.is_accessible_from(self.item_def_id(), tcx)
&& tcx.all_impls(*trait_def_id)
.any(|impl_def_id| {
let impl_header = tcx.impl_trait_header(impl_def_id);
impl_header.is_some_and(|header| {
let trait_ref = header.trait_ref.instantiate(
tcx,
infcx.fresh_args_for_item(DUMMY_SP, impl_def_id),
);
let value = tcx.fold_regions(qself_ty, |_, _| tcx.lifetimes.re_erased);
// FIXME: Don't bother dealing with non-lifetime binders here...
if value.has_escaping_bound_vars() {
return false;
}
infcx
.can_eq(
ty::ParamEnv::empty(),
trait_ref.self_ty(),
value,
) && header.polarity != ty::ImplPolarity::Negative
})
})
})
.map(|trait_def_id| tcx.def_path_str(trait_def_id))
.collect()
}
/// Lower a qualified path to a type.
#[instrument(level = "debug", skip_all)]
fn lower_qpath(
&self,
span: Span,
opt_self_ty: Option<Ty<'tcx>>,
item_def_id: DefId,
trait_segment: &hir::PathSegment<'tcx>,
item_segment: &hir::PathSegment<'tcx>,
constness: ty::BoundConstness,
) -> Ty<'tcx> {
let tcx = self.tcx();
let trait_def_id = tcx.parent(item_def_id);
debug!(?trait_def_id);
let Some(self_ty) = opt_self_ty else {
let path_str = tcx.def_path_str(trait_def_id);
let def_id = self.item_def_id();
debug!(item_def_id = ?def_id);
let parent_def_id = def_id
.as_local()
.map(|def_id| tcx.local_def_id_to_hir_id(def_id))
.map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
debug!(?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 == trait_def_id;
let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
let type_names = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
vec!["Self".to_string()]
} else {
// Find all the types that have an `impl` for the trait.
tcx.all_impls(trait_def_id)
.filter_map(|impl_def_id| tcx.impl_trait_header(impl_def_id))
.filter(|header| {
// Consider only accessible traits
tcx.visibility(trait_def_id).is_accessible_from(self.item_def_id(), tcx)
&& header.polarity != ty::ImplPolarity::Negative
})
.map(|header| header.trait_ref.instantiate_identity().self_ty())
// We don't care about blanket impls.
.filter(|self_ty| !self_ty.has_non_region_param())
.map(|self_ty| tcx.erase_regions(self_ty).to_string())
.collect()
};
// FIXME: also look at `tcx.generics_of(self.item_def_id()).params` any that
// references the trait. Relevant for the first case in
// `src/test/ui/associated-types/associated-types-in-ambiguous-context.rs`
let reported = self.report_ambiguous_assoc_ty(
span,
&type_names,
&[path_str],
item_segment.ident.name,
);
return Ty::new_error(tcx, reported);
};
debug!(?self_ty);
let trait_ref =
self.lower_mono_trait_ref(span, trait_def_id, self_ty, trait_segment, false, constness);
debug!(?trait_ref);
let item_args =
self.lower_generic_args_of_assoc_item(span, item_def_id, item_segment, trait_ref.args);
Ty::new_projection(tcx, item_def_id, item_args)
}
pub fn prohibit_generic_args<'a>(
&self,
segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
err_extend: GenericsArgsErrExtend<'_>,
) -> Result<(), ErrorGuaranteed> {
let args_visitors = segments.clone().flat_map(|segment| segment.args().args);
let mut result = Ok(());
if let Some(_) = args_visitors.clone().next() {
result = Err(self.report_prohibit_generics_error(
segments.clone(),
args_visitors,
err_extend,
));
}
for segment in segments {
// Only emit the first error to avoid overloading the user with error messages.
if let Some(b) = segment.args().bindings.first() {
return Err(prohibit_assoc_item_binding(self.tcx(), b, None));
}
}
result
}
/// Probe path segments that are semantically allowed to have generic arguments.
///
/// ### Example
///
/// ```ignore (illustrative)
/// Option::None::<()>
/// // ^^^^ permitted to have generic args
///
/// // ==> [GenericPathSegment(Option_def_id, 1)]
///
/// Option::<()>::None
/// // ^^^^^^ ^^^^ *not* permitted to have generic args
/// // permitted to have generic args
///
/// // ==> [GenericPathSegment(Option_def_id, 0)]
/// ```
// FIXME(eddyb, varkor) handle type paths here too, not just value ones.
pub fn probe_generic_path_segments(
&self,
segments: &[hir::PathSegment<'_>],
self_ty: Option<Ty<'tcx>>,
kind: DefKind,
def_id: DefId,
span: Span,
) -> Vec<GenericPathSegment> {
// We need to extract the generic arguments 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 generic arguments are declared in the type space.
//
// 2. Reference to a constructor of an enum variant:
//
// enum E<T> { Foo(...) }
//
// In this case, the generic arguments are defined in the type space,
// but may be specified either on the type or the variant.
//
// 3. Reference to a free function or 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 generic
// arguments. However, in this case, those arguments are declared on
// a value, and hence are in the value space.
//
// 4. Reference to an associated function or constant:
//
// impl<A> SomeStruct<A> {
// fn foo<B>(...) {}
// }
//
// Here we can have a path like `a::b::SomeStruct::<A>::foo::<B>`,
// in which case generic arguments may appear in two places. The
// penultimate segment, `SomeStruct::<A>`, contains generic arguments
// in the type space, and the final segment, `foo::<B>` contains
// generic arguments in value 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 generic_segments = 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);
generic_segments.push(GenericPathSegment(generics_def_id, last));
}
// Case 2. Reference to a variant constructor.
DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
let (generics_def_id, index) = if let Some(self_ty) = self_ty {
let adt_def = self.probe_adt(span, self_ty).unwrap();
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);
}
// `DefKind::Variant` -> `DefKind::Enum`
let enum_def_id = tcx.parent(def_id);
(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)
};
generic_segments.push(GenericPathSegment(generics_def_id, index));
}
// Case 3. Reference to a top-level value.
DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static { .. } => {
generic_segments.push(GenericPathSegment(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);
generic_segments.push(GenericPathSegment(generics.parent.unwrap(), last - 1));
}
generic_segments.push(GenericPathSegment(def_id, last));
}
kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
}
debug!(?generic_segments);
generic_segments
}
/// Lower a type `Path` to a type.
#[instrument(level = "debug", skip_all)]
pub fn lower_path(
&self,
opt_self_ty: Option<Ty<'tcx>>,
path: &hir::Path<'tcx>,
hir_id: HirId,
permit_variants: bool,
) -> Ty<'tcx> {
debug!(?path.res, ?opt_self_ty, ?path.segments);
let tcx = self.tcx();
let span = path.span;
match path.res {
Res::Def(DefKind::OpaqueTy, did) => {
// Check for desugared `impl Trait`.
assert!(tcx.is_type_alias_impl_trait(did));
let item_segment = path.segments.split_last().unwrap();
let _ = self
.prohibit_generic_args(item_segment.1.iter(), GenericsArgsErrExtend::OpaqueTy);
let args = self.lower_generic_args_of_path_segment(span, did, item_segment.0);
Ty::new_opaque(tcx, did, args)
}
Res::Def(
DefKind::Enum
| DefKind::TyAlias
| DefKind::Struct
| DefKind::Union
| DefKind::ForeignTy,
did,
) => {
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.split_last().unwrap().1.iter(),
GenericsArgsErrExtend::None,
);
self.lower_path_segment(span, did, path.segments.last().unwrap())
}
Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
// Lower "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 generic_segments =
self.probe_generic_path_segments(path.segments, None, kind, def_id, span);
let indices: FxHashSet<_> =
generic_segments.iter().map(|GenericPathSegment(_, index)| index).collect();
let _ = self.prohibit_generic_args(
path.segments.iter().enumerate().filter_map(|(index, seg)| {
if !indices.contains(&index) { Some(seg) } else { None }
}),
GenericsArgsErrExtend::DefVariant,
);
let GenericPathSegment(def_id, index) = generic_segments.last().unwrap();
self.lower_path_segment(span, *def_id, &path.segments[*index])
}
Res::Def(DefKind::TyParam, def_id) => {
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.iter(),
GenericsArgsErrExtend::TyParam(def_id),
);
self.lower_ty_param(hir_id)
}
Res::SelfTyParam { .. } => {
// `Self` in trait or type alias.
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.iter(),
if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments {
GenericsArgsErrExtend::SelfTyParam(
ident.span.shrink_to_hi().to(args.span_ext),
)
} else {
GenericsArgsErrExtend::None
},
);
tcx.types.self_param
}
Res::SelfTyAlias { alias_to: def_id, forbid_generic, .. } => {
// `Self` in impl (we know the concrete type).
assert_eq!(opt_self_ty, None);
// Try to evaluate any array length constants.
let ty = tcx.at(span).type_of(def_id).instantiate_identity();
let _ = self.prohibit_generic_args(
path.segments.iter(),
GenericsArgsErrExtend::SelfTyAlias { def_id, span },
);
// HACK(min_const_generics): Forbid generic `Self` types
// here as we can't easily do that during nameres.
//
// We do this before normalization as we otherwise allow
// ```rust
// trait AlwaysApplicable { type Assoc; }
// impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
//
// trait BindsParam<T> {
// type ArrayTy;
// }
// impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
// type ArrayTy = [u8; Self::MAX];
// }
// ```
// Note that the normalization happens in the param env of
// the anon const, which is empty. This is why the
// `AlwaysApplicable` impl needs a `T: ?Sized` bound for
// this to compile if we were to normalize here.
if forbid_generic && ty.has_param() {
let mut err = tcx.dcx().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(impl_),
..
})) = tcx.hir().get_if_local(def_id)
{
err.span_note(impl_.self_ty.span, "not a concrete type");
}
let reported = err.emit();
self.set_tainted_by_errors(reported);
Ty::new_error(tcx, reported)
} else {
ty
}
}
Res::Def(DefKind::AssocTy, def_id) => {
debug_assert!(path.segments.len() >= 2);
let _ = self.prohibit_generic_args(
path.segments[..path.segments.len() - 2].iter(),
GenericsArgsErrExtend::None,
);
// HACK: until we support `<Type as ~const Trait>`, assume all of them are.
let constness = if tcx.has_attr(tcx.parent(def_id), sym::const_trait) {
ty::BoundConstness::ConstIfConst
} else {
ty::BoundConstness::NotConst
};
self.lower_qpath(
span,
opt_self_ty,
def_id,
&path.segments[path.segments.len() - 2],
path.segments.last().unwrap(),
constness,
)
}
Res::PrimTy(prim_ty) => {
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.iter(),
GenericsArgsErrExtend::PrimTy(prim_ty),
);
match prim_ty {
hir::PrimTy::Bool => tcx.types.bool,
hir::PrimTy::Char => tcx.types.char,
hir::PrimTy::Int(it) => Ty::new_int(tcx, ty::int_ty(it)),
hir::PrimTy::Uint(uit) => Ty::new_uint(tcx, ty::uint_ty(uit)),
hir::PrimTy::Float(ft) => Ty::new_float(tcx, ty::float_ty(ft)),
hir::PrimTy::Str => tcx.types.str_,
}
}
Res::Err => {
let e = self
.tcx()
.dcx()
.span_delayed_bug(path.span, "path with `Res::Err` but no error emitted");
self.set_tainted_by_errors(e);
Ty::new_error(self.tcx(), e)
}
Res::Def(..) => {
assert_eq!(
path.segments.get(0).map(|seg| seg.ident.name),
Some(kw::SelfUpper),
"only expected incorrect resolution for `Self`"
);
Ty::new_error(
self.tcx(),
self.tcx().dcx().span_delayed_bug(span, "incorrect resolution for `Self`"),
)
}
_ => span_bug!(span, "unexpected resolution: {:?}", path.res),
}
}
/// Lower a type parameter from the HIR to our internal notion of a type.
///
/// Early-bound type parameters get lowered to [`ty::Param`]
/// and late-bound ones to [`ty::Bound`].
pub(crate) fn lower_ty_param(&self, hir_id: HirId) -> Ty<'tcx> {
let tcx = self.tcx();
match tcx.named_bound_var(hir_id) {
Some(rbv::ResolvedArg::LateBound(debruijn, index, def_id)) => {
let name = tcx.item_name(def_id);
let br = ty::BoundTy {
var: ty::BoundVar::from_u32(index),
kind: ty::BoundTyKind::Param(def_id, name),
};
Ty::new_bound(tcx, debruijn, br)
}
Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
let def_id = def_id.expect_local();
let item_def_id = tcx.hir().ty_param_owner(def_id);
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&def_id.to_def_id()];
Ty::new_param(tcx, index, tcx.hir().ty_param_name(def_id))
}
Some(rbv::ResolvedArg::Error(guar)) => Ty::new_error(tcx, guar),
arg => bug!("unexpected bound var resolution for {hir_id:?}: {arg:?}"),
}
}
/// Lower a const parameter from the HIR to our internal notion of a constant.
///
/// Early-bound const parameters get lowered to [`ty::ConstKind::Param`]
/// and late-bound ones to [`ty::ConstKind::Bound`].
pub(crate) fn lower_const_param(&self, hir_id: HirId, param_ty: Ty<'tcx>) -> Const<'tcx> {
let tcx = self.tcx();
match tcx.named_bound_var(hir_id) {
Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
// Find the name and index of the const parameter by indexing the generics of
// the parent item and construct a `ParamConst`.
let item_def_id = tcx.parent(def_id);
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&def_id];
let name = tcx.item_name(def_id);
ty::Const::new_param(tcx, ty::ParamConst::new(index, name), param_ty)
}
Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
ty::Const::new_bound(tcx, debruijn, ty::BoundVar::from_u32(index), param_ty)
}
Some(rbv::ResolvedArg::Error(guar)) => ty::Const::new_error(tcx, guar, param_ty),
arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", hir_id),
}
}
/// Lower a type from the HIR to our internal notion of a type.
pub fn lower_ty(&self, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
self.lower_ty_common(hir_ty, false, false)
}
/// Lower a type inside of a path from the HIR to our internal notion of a type.
pub fn lower_ty_in_path(&self, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
self.lower_ty_common(hir_ty, false, true)
}
fn check_delegation_constraints(&self, sig_id: DefId, span: Span, emit: bool) -> bool {
let mut error_occured = false;
let sig_span = self.tcx().def_span(sig_id);
let mut try_emit = |descr| {
if emit {
self.tcx().dcx().emit_err(crate::errors::NotSupportedDelegation {
span,
descr,
callee_span: sig_span,
});
}
error_occured = true;
};
if let Some(node) = self.tcx().hir().get_if_local(sig_id)
&& let Some(decl) = node.fn_decl()
&& let hir::FnRetTy::Return(ty) = decl.output
&& let hir::TyKind::InferDelegation(_, _) = ty.kind
{
try_emit("recursive delegation");
}
let sig_generics = self.tcx().generics_of(sig_id);
let parent = self.tcx().parent(self.item_def_id());
let parent_generics = self.tcx().generics_of(parent);
let parent_is_trait = (self.tcx().def_kind(parent) == DefKind::Trait) as usize;
let sig_has_self = sig_generics.has_self as usize;
if sig_generics.count() > sig_has_self || parent_generics.count() > parent_is_trait {
try_emit("delegation with early bound generics");
}
// There is no way to instantiate `Self` param for caller if
// 1. callee is a trait method
// 2. delegation item isn't an associative item
if let DefKind::AssocFn = self.tcx().def_kind(sig_id)
&& let DefKind::Fn = self.tcx().def_kind(self.item_def_id())
&& self.tcx().associated_item(sig_id).container
== ty::AssocItemContainer::TraitContainer
{
try_emit("delegation to a trait method from a free function");
}
error_occured
}
fn lower_delegation_ty(
&self,
sig_id: DefId,
idx: hir::InferDelegationKind,
span: Span,
) -> Ty<'tcx> {
if self.check_delegation_constraints(sig_id, span, idx == hir::InferDelegationKind::Output)
{
let e = self.tcx().dcx().span_delayed_bug(span, "not supported delegation case");
self.set_tainted_by_errors(e);
return Ty::new_error(self.tcx(), e);
};
let sig = self.tcx().fn_sig(sig_id);
let sig_generics = self.tcx().generics_of(sig_id);
let parent = self.tcx().parent(self.item_def_id());
let parent_def_kind = self.tcx().def_kind(parent);
let sig = if let DefKind::Impl { .. } = parent_def_kind
&& sig_generics.has_self
{
// Generic params can't be here except the trait self type.
// They are not supported yet.
assert_eq!(sig_generics.count(), 1);
assert_eq!(self.tcx().generics_of(parent).count(), 0);
let self_ty = self.tcx().type_of(parent).instantiate_identity();
let generic_self_ty = ty::GenericArg::from(self_ty);
let args = self.tcx().mk_args_from_iter(std::iter::once(generic_self_ty));
sig.instantiate(self.tcx(), args)
} else {
sig.instantiate_identity()
};
// Bound vars are also inherited from `sig_id`.
// They will be rebound later in `lower_fn_ty`.
let sig = sig.skip_binder();
match idx {
hir::InferDelegationKind::Input(id) => sig.inputs()[id],
hir::InferDelegationKind::Output => sig.output(),
}
}
/// Lower a type from the HIR to our internal notion of a type given some extra data for diagnostics.
///
/// Extra diagnostic data:
///
/// 1. `borrowed`: Whether trait object types are borrowed like in `&dyn Trait`.
/// Used to avoid emitting redundant errors.
/// 2. `in_path`: Whether the type appears inside of a path.
/// Used to provide correct diagnostics for bare trait object types.
#[instrument(level = "debug", skip(self), ret)]
fn lower_ty_common(&self, hir_ty: &hir::Ty<'tcx>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
let tcx = self.tcx();
let result_ty = match &hir_ty.kind {
hir::TyKind::InferDelegation(sig_id, idx) => {
self.lower_delegation_ty(*sig_id, *idx, hir_ty.span)
}
hir::TyKind::Slice(ty) => Ty::new_slice(tcx, self.lower_ty(ty)),
hir::TyKind::Ptr(mt) => Ty::new_ptr(tcx, self.lower_ty(mt.ty), mt.mutbl),
hir::TyKind::Ref(region, mt) => {
let r = self.lower_lifetime(region, None);
debug!(?r);
let t = self.lower_ty_common(mt.ty, true, false);
Ty::new_ref(tcx, r, t, mt.mutbl)
}
hir::TyKind::Never => tcx.types.never,
hir::TyKind::Tup(fields) => {
Ty::new_tup_from_iter(tcx, fields.iter().map(|t| self.lower_ty(t)))
}
hir::TyKind::AnonAdt(item_id) => {
let _guard = debug_span!("AnonAdt");
let did = item_id.owner_id.def_id;
let adt_def = tcx.adt_def(did);
let args = ty::GenericArgs::for_item(tcx, did.to_def_id(), |param, _| {
tcx.mk_param_from_def(param)
});
debug!(?args);
Ty::new_adt(tcx, adt_def, tcx.mk_args(args))
}
hir::TyKind::BareFn(bf) => {
require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, hir_ty.span);
Ty::new_fn_ptr(
tcx,
self.lower_fn_ty(
hir_ty.hir_id,
bf.unsafety,
bf.abi,
bf.decl,
None,
Some(hir_ty),
),
)
}
hir::TyKind::TraitObject(bounds, lifetime, repr) => {
self.prohibit_or_lint_bare_trait_object_ty(hir_ty, in_path);
let repr = match repr {
TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
TraitObjectSyntax::DynStar => ty::DynStar,
};
self.lower_trait_object_ty(
hir_ty.span,
hir_ty.hir_id,
bounds,
lifetime,
borrowed,
repr,
)
}
hir::TyKind::Path(hir::QPath::Resolved(maybe_qself, path)) => {
debug!(?maybe_qself, ?path);
let opt_self_ty = maybe_qself.as_ref().map(|qself| self.lower_ty(qself));
self.lower_path(opt_self_ty, path, hir_ty.hir_id, false)
}
&hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
let opaque_ty = tcx.hir().item(item_id);
match opaque_ty.kind {
hir::ItemKind::OpaqueTy(&hir::OpaqueTy { .. }) => {
let local_def_id = item_id.owner_id.def_id;
// If this is an RPITIT and we are using the new RPITIT lowering scheme, we
// generate the def_id of an associated type for the trait and return as
// type a projection.
let def_id = if in_trait {
tcx.associated_type_for_impl_trait_in_trait(local_def_id).to_def_id()
} else {
local_def_id.to_def_id()
};
self.lower_opaque_ty(def_id, lifetimes, in_trait)
}
ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
}
}
hir::TyKind::Path(hir::QPath::TypeRelative(qself, segment)) => {
debug!(?qself, ?segment);
let ty = self.lower_ty_common(qself, false, true);
self.lower_assoc_path(hir_ty.hir_id, hir_ty.span, ty, qself, segment, false)
.map(|(ty, _, _)| ty)
.unwrap_or_else(|guar| Ty::new_error(tcx, guar))
}
&hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
let def_id = tcx.require_lang_item(lang_item, Some(span));
let (args, _) = self.lower_generic_args_of_path(
span,
def_id,
&[],
&hir::PathSegment::invalid(),
None,
ty::BoundConstness::NotConst,
);
tcx.at(span).type_of(def_id).instantiate(tcx, args)
}
hir::TyKind::Array(ty, length) => {
let length = match length {
hir::ArrayLen::Infer(inf) => self.ct_infer(tcx.types.usize, None, inf.span),
hir::ArrayLen::Body(constant) => {
ty::Const::from_anon_const(tcx, constant.def_id)
}
};
Ty::new_array_with_const_len(tcx, self.lower_ty(ty), length)
}
hir::TyKind::Typeof(e) => tcx.type_of(e.def_id).instantiate_identity(),
hir::TyKind::Infer => {
// Infer also appears as the type of arguments or return
// values in an 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, hir_ty.span)
}
hir::TyKind::Pat(ty, pat) => {
let ty = self.lower_ty(ty);
let pat_ty = match pat.kind {
hir::PatKind::Wild => {
let err = tcx.dcx().emit_err(WildPatTy { span: pat.span });
Ty::new_error(tcx, err)
}
hir::PatKind::Range(start, end, include_end) => {
let expr_to_const = |expr: &'tcx hir::Expr<'tcx>| -> ty::Const<'tcx> {
let (expr, neg) = match expr.kind {
hir::ExprKind::Unary(hir::UnOp::Neg, negated) => {
(negated, Some((expr.hir_id, expr.span)))
}
_ => (expr, None),
};
let c = match &expr.kind {
hir::ExprKind::Lit(lit) => {
let lit_input =
LitToConstInput { lit: &lit.node, ty, neg: neg.is_some() };
match tcx.lit_to_const(lit_input) {
Ok(c) => c,
Err(LitToConstError::Reported(err)) => {
ty::Const::new_error(tcx, err, ty)
}
Err(LitToConstError::TypeError) => todo!(),
}
}
hir::ExprKind::Path(hir::QPath::Resolved(
_,
&hir::Path {
res: Res::Def(DefKind::ConstParam, def_id), ..
},
)) => {
let ty = tcx
.type_of(def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic");
self.lower_const_param(expr.hir_id, ty)
}
_ => {
let err = tcx
.dcx()
.emit_err(crate::errors::NonConstRange { span: expr.span });
ty::Const::new_error(tcx, err, ty)
}
};
self.record_ty(expr.hir_id, c.ty(), expr.span);
if let Some((id, span)) = neg {
self.record_ty(id, c.ty(), span);
}
c
};
let start = start.map(expr_to_const);
let end = end.map(expr_to_const);
let include_end = match include_end {
hir::RangeEnd::Included => true,
hir::RangeEnd::Excluded => false,
};
let pat = tcx.mk_pat(ty::PatternKind::Range { start, end, include_end });
Ty::new_pat(tcx, ty, pat)
}
hir::PatKind::Err(e) => Ty::new_error(tcx, e),
_ => Ty::new_error_with_message(
tcx,
pat.span,
format!("unsupported pattern for pattern type: {pat:#?}"),
),
};
self.record_ty(pat.hir_id, ty, pat.span);
pat_ty
}
hir::TyKind::Err(guar) => Ty::new_error(tcx, *guar),
};
self.record_ty(hir_ty.hir_id, result_ty, hir_ty.span);
result_ty
}
/// Lower an opaque type (i.e., an existential impl-Trait type) from the HIR.
#[instrument(level = "debug", skip_all, ret)]
fn lower_opaque_ty(
&self,
def_id: DefId,
lifetimes: &[hir::GenericArg<'_>],
in_trait: bool,
) -> Ty<'tcx> {
debug!(?def_id, ?lifetimes);
let tcx = self.tcx();
let generics = tcx.generics_of(def_id);
debug!(?generics);
let args = ty::GenericArgs::for_item(tcx, def_id, |param, _| {
// We use `generics.count() - lifetimes.len()` here instead of `generics.parent_count`
// since return-position impl trait in trait squashes all of the generics from its source fn
// into its own generics, so the opaque's "own" params isn't always just lifetimes.
if let Some(i) = (param.index as usize).checked_sub(generics.count() - lifetimes.len())
{
// Resolve our own lifetime parameters.
let GenericParamDefKind::Lifetime { .. } = param.kind else {
span_bug!(
tcx.def_span(param.def_id),
"only expected lifetime for opaque's own generics, got {:?}",
param.kind
);
};
let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] else {
bug!(
"expected lifetime argument for param {param:?}, found {:?}",
&lifetimes[i]
)
};
self.lower_lifetime(lifetime, None).into()
} else {
tcx.mk_param_from_def(param)
}
});
debug!(?args);
if in_trait {
Ty::new_projection(tcx, def_id, args)
} else {
Ty::new_opaque(tcx, def_id, args)
}
}
pub fn lower_arg_ty(&self, ty: &hir::Ty<'tcx>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
match ty.kind {
hir::TyKind::Infer if let Some(expected_ty) = expected_ty => {
self.record_ty(ty.hir_id, expected_ty, ty.span);
expected_ty
}
_ => self.lower_ty(ty),
}
}
/// Lower a function type from the HIR to our internal notion of a function signature.
#[instrument(level = "debug", skip(self, hir_id, unsafety, abi, decl, generics, hir_ty), ret)]
pub fn lower_fn_ty(
&self,
hir_id: HirId,
unsafety: hir::Unsafety,
abi: abi::Abi,
decl: &hir::FnDecl<'tcx>,
generics: Option<&hir::Generics<'_>>,
hir_ty: Option<&hir::Ty<'_>>,
) -> ty::PolyFnSig<'tcx> {
let tcx = self.tcx();
let bound_vars = tcx.late_bound_vars(hir_id);
debug!(?bound_vars);
// We proactively collect all the inferred type params to emit a single error per fn def.
let mut visitor = HirPlaceholderCollector::default();
let mut infer_replacements = vec![];
if let Some(generics) = generics {
walk_generics(&mut visitor, generics);
}
let input_tys: Vec<_> = decl
.inputs
.iter()
.enumerate()
.map(|(i, a)| {
if let hir::TyKind::Infer = a.kind
&& !self.allow_infer()
{
if let Some(suggested_ty) =
self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
{
infer_replacements.push((a.span, suggested_ty.to_string()));
return Ty::new_error_with_message(
self.tcx(),
a.span,
suggested_ty.to_string(),
);
}
}
// Only visit the type looking for `_` if we didn't fix the type above
visitor.visit_ty(a);
self.lower_arg_ty(a, None)
})
.collect();
let output_ty = match decl.output {
hir::FnRetTy::Return(output) => {
if let hir::TyKind::Infer = output.kind
&& !self.allow_infer()
&& let Some(suggested_ty) =
self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
{
infer_replacements.push((output.span, suggested_ty.to_string()));
Ty::new_error_with_message(self.tcx(), output.span, suggested_ty.to_string())
} else {
visitor.visit_ty(output);
self.lower_ty(output)
}
}
hir::FnRetTy::DefaultReturn(..) => tcx.types.unit,
};
debug!(?output_ty);
let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
if !self.allow_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
// 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_infer` gates this behavior. We check for the presence of
// `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
let mut diag = crate::collect::placeholder_type_error_diag(
tcx,
generics,
visitor.0,
infer_replacements.iter().map(|(s, _)| *s).collect(),
true,
hir_ty,
"function",
);
if !infer_replacements.is_empty() {
diag.multipart_suggestion(
format!(
"try replacing `_` with the type{} in the corresponding trait method signature",
rustc_errors::pluralize!(infer_replacements.len()),
),
infer_replacements,
Applicability::MachineApplicable,
);
}
self.set_tainted_by_errors(diag.emit());
}
// 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_code_err!(
tcx.dcx(),
decl.output.span(),
E0581,
"return type references {}, which is not constrained by the fn input types",
br_name
)
});
bare_fn_ty
}
/// Given a fn_hir_id for a impl function, suggest the type that is found on the
/// corresponding function in the trait that the impl implements, if it exists.
/// If arg_idx is Some, then it corresponds to an input type index, otherwise it
/// corresponds to the return type.
fn suggest_trait_fn_ty_for_impl_fn_infer(
&self,
fn_hir_id: HirId,
arg_idx: Option<usize>,
) -> Option<Ty<'tcx>> {
let tcx = self.tcx();
let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
tcx.hir_node(fn_hir_id)
else {
return None;
};
let i = tcx.parent_hir_node(fn_hir_id).expect_item().expect_impl();
let trait_ref = self.lower_impl_trait_ref(i.of_trait.as_ref()?, self.lower_ty(i.self_ty));
let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
tcx,
*ident,
ty::AssocKind::Fn,
trait_ref.def_id,
)?;
let fn_sig = tcx.fn_sig(assoc.def_id).instantiate(
tcx,
trait_ref.args.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
);
let fn_sig = tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), fn_sig);
Some(if let Some(arg_idx) = arg_idx {
*fn_sig.inputs().get(arg_idx)?
} else {
fn_sig.output()
})
}
#[instrument(level = "trace", skip(self, generate_err))]
fn validate_late_bound_regions(
&self,
constrained_regions: FxHashSet<ty::BoundRegionKind>,
referenced_regions: FxHashSet<ty::BoundRegionKind>,
generate_err: impl Fn(&str) -> Diag<'tcx>,
) {
for br in referenced_regions.difference(&constrained_regions) {
let br_name = match *br {
ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon | ty::BrEnv => {
"an anonymous lifetime".to_string()
}
ty::BrNamed(_, name) => format!("lifetime `{name}`"),
};
let mut err = generate_err(&br_name);
if let ty::BrNamed(_, kw::UnderscoreLifetime) | 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 or opaque type are not considered constrained",
);
err.note("consider introducing a named lifetime parameter");
}
self.set_tainted_by_errors(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`.
#[instrument(level = "debug", skip(self, span), ret)]
fn compute_object_lifetime_bound(
&self,
span: Span,
existential_predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
) -> Option<ty::Region<'tcx>> // if None, use the default
{
let tcx = self.tcx();
// 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| r.is_static()) {
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) {
self.set_tainted_by_errors(tcx.dcx().emit_err(AmbiguousLifetimeBound { span }));
}
Some(r)
}
}
fn assoc_kind_str(kind: ty::AssocKind) -> &'static str {
match kind {
ty::AssocKind::Fn => "function",
ty::AssocKind::Const => "constant",
ty::AssocKind::Type => "type",
}
}