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rust / rust / 1ce9c977ffcff7c3b12bfe5629a682da0e74a7a1 / . / 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;
mod cmse;
mod dyn_compatibility;
pub mod errors;
pub mod generics;
mod lint;
use std::assert_matches::assert_matches;
use std::slice;
use rustc_ast::TraitObjectSyntax;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_errors::codes::*;
use rustc_errors::{
Applicability, Diag, DiagCtxtHandle, ErrorGuaranteed, FatalError, struct_span_code_err,
};
use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{self as hir, AnonConst, GenericArg, GenericArgs, HirId};
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::DynCompatibilityViolation;
use rustc_macros::{TypeFoldable, TypeVisitable};
use rustc_middle::middle::stability::AllowUnstable;
use rustc_middle::mir::interpret::LitToConstInput;
use rustc_middle::ty::print::PrintPolyTraitRefExt as _;
use rustc_middle::ty::{
self, Const, GenericArgKind, GenericArgsRef, GenericParamDefKind, Ty, TyCtxt, TypeVisitableExt,
TypingMode, Upcast, fold_regions,
};
use rustc_middle::{bug, span_bug};
use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
use rustc_session::parse::feature_err;
use rustc_span::{DUMMY_SP, Ident, Span, kw, sym};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::wf::object_region_bounds;
use rustc_trait_selection::traits::{self, FulfillmentError};
use tracing::{debug, instrument};
use crate::check::check_abi;
use crate::errors::{AmbiguousLifetimeBound, BadReturnTypeNotation};
use crate::hir_ty_lowering::errors::{GenericsArgsErrExtend, prohibit_assoc_item_constraint};
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;
/// 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 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. This mode exists to
/// side-step query cycles when lowering associated types.
SelfTraitThatDefines(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,
/// Filter only the `[const]` bounds, which are lowered into `HostEffect` clauses.
ConstIfConst,
/// Filter only the `[const]` bounds which are *also* in the supertrait position.
SelfConstIfConst,
}
#[derive(Debug)]
pub enum RegionInferReason<'a> {
/// Lifetime on a trait object that is spelled explicitly, e.g. `+ 'a` or `+ '_`.
ExplicitObjectLifetime,
/// A trait object's lifetime when it is elided, e.g. `dyn Any`.
ObjectLifetimeDefault,
/// Generic lifetime parameter
Param(&'a ty::GenericParamDef),
RegionPredicate,
Reference,
OutlivesBound,
}
#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Debug)]
pub struct InherentAssocCandidate {
pub impl_: DefId,
pub assoc_item: DefId,
pub scope: DefId,
}
/// 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>;
fn dcx(&self) -> DiagCtxtHandle<'_>;
/// Returns the [`LocalDefId`] of the overarching item whose constituents get lowered.
fn item_def_id(&self) -> LocalDefId;
/// Returns the region to use when a lifetime is omitted (and not elided).
fn re_infer(&self, span: Span, reason: RegionInferReason<'_>) -> 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, param: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx>;
fn register_trait_ascription_bounds(
&self,
bounds: Vec<(ty::Clause<'tcx>, Span)>,
hir_id: HirId,
span: Span,
);
/// 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_ident: Ident,
) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]>;
fn select_inherent_assoc_candidates(
&self,
span: Span,
self_ty: Ty<'tcx>,
candidates: Vec<InherentAssocCandidate>,
) -> (Vec<InherentAssocCandidate>, Vec<FulfillmentError<'tcx>>);
/// Lower a path to an associated item (of a trait) 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_item_path(
&self,
span: Span,
item_def_id: DefId,
item_segment: &hir::PathSegment<'tcx>,
poly_trait_ref: ty::PolyTraitRef<'tcx>,
) -> Result<(DefId, GenericArgsRef<'tcx>), ErrorGuaranteed>;
fn lower_fn_sig(
&self,
decl: &hir::FnDecl<'tcx>,
generics: Option<&hir::Generics<'_>>,
hir_id: HirId,
hir_ty: Option<&hir::Ty<'_>>,
) -> (Vec<Ty<'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>>;
/// 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
}
/// Performs minimalistic dyn compat checks outside of bodies, but full within bodies.
/// Outside of bodies we could end up in cycles, so we delay most checks to later phases.
fn dyn_compatibility_violations(&self, trait_def_id: DefId) -> Vec<DynCompatibilityViolation>;
}
/// The "qualified self" of an associated item path.
///
/// For diagnostic purposes only.
enum AssocItemQSelf {
Trait(DefId),
TyParam(LocalDefId, Span),
SelfTyAlias,
}
impl AssocItemQSelf {
fn to_string(&self, tcx: TyCtxt<'_>) -> String {
match *self {
Self::Trait(def_id) => tcx.def_path_str(def_id),
Self::TyParam(def_id, _) => tcx.hir_ty_param_name(def_id).to_string(),
Self::SelfTyAlias => kw::SelfUpper.to_string(),
}
}
}
/// In some cases, [`hir::ConstArg`]s that are being used in the type system
/// through const generics need to have their type "fed" to them
/// using the query system.
///
/// Use this enum with `<dyn HirTyLowerer>::lower_const_arg` to instruct it with the
/// desired behavior.
#[derive(Debug, Clone, Copy)]
pub enum FeedConstTy<'a, 'tcx> {
/// Feed the type.
///
/// The `DefId` belongs to the const param that we are supplying
/// this (anon) const arg to.
///
/// The list of generic args is used to instantiate the parameters
/// used by the type of the const param specified by `DefId`.
Param(DefId, &'a [ty::GenericArg<'tcx>]),
/// Don't feed the type.
No,
}
#[derive(Debug, Clone, Copy)]
enum LowerTypeRelativePathMode {
Type(PermitVariants),
Const,
}
impl LowerTypeRelativePathMode {
fn assoc_tag(self) -> ty::AssocTag {
match self {
Self::Type(_) => ty::AssocTag::Type,
Self::Const => ty::AssocTag::Const,
}
}
fn def_kind(self) -> DefKind {
match self {
Self::Type(_) => DefKind::AssocTy,
Self::Const => DefKind::AssocConst,
}
}
fn permit_variants(self) -> PermitVariants {
match self {
Self::Type(permit_variants) => permit_variants,
// FIXME(mgca): Support paths like `Option::<T>::None` or `Option::<T>::Some` which
// resolve to const ctors/fn items respectively.
Self::Const => PermitVariants::No,
}
}
}
/// Whether to permit a path to resolve to an enum variant.
#[derive(Debug, Clone, Copy)]
pub enum PermitVariants {
Yes,
No,
}
#[derive(Debug, Clone, Copy)]
enum TypeRelativePath<'tcx> {
AssocItem(DefId, GenericArgsRef<'tcx>),
Variant { adt: Ty<'tcx>, variant_did: DefId },
}
/// 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, Debug)]
pub struct GenericArgCountMismatch {
pub reported: ErrorGuaranteed,
/// A list of indices of arguments provided that were not valid.
pub invalid_args: Vec<usize>,
}
/// 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,
preceding_args: &[ty::GenericArg<'tcx>],
param: &ty::GenericParamDef,
arg: &GenericArg<'tcx>,
) -> ty::GenericArg<'tcx>;
fn inferred_kind(
&mut self,
preceding_args: &[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,
reason: RegionInferReason<'_>,
) -> ty::Region<'tcx> {
if let Some(resolved) = self.tcx().named_bound_var(lifetime.hir_id) {
self.lower_resolved_lifetime(resolved)
} else {
self.re_infer(lifetime.ident.span, reason)
}
}
/// 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_resolved_lifetime(&self, resolved: rbv::ResolvedArg) -> 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 resolved {
rbv::ResolvedArg::StaticLifetime => tcx.lifetimes.re_static,
rbv::ResolvedArg::LateBound(debruijn, index, def_id) => {
let name = lifetime_name(def_id);
let br = ty::BoundRegion {
var: ty::BoundVar::from_u32(index),
kind: ty::BoundRegionKind::Named(def_id.to_def_id(), name),
};
ty::Region::new_bound(tcx, debruijn, br)
}
rbv::ResolvedArg::EarlyBound(def_id) => {
let name = tcx.hir_ty_param_name(def_id);
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::Region::new_early_param(tcx, ty::EarlyParamRegion { index, name })
}
rbv::ResolvedArg::Free(scope, id) => {
let name = lifetime_name(id);
ty::Region::new_late_param(
tcx,
scope.to_def_id(),
ty::LateParamRegionKind::Named(id.to_def_id(), name),
)
// (*) -- not late-bound, won't change
}
rbv::ResolvedArg::Error(guar) => ty::Region::new_error(tcx, guar),
}
}
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);
if let Some(c) = item_segment.args().constraints.first() {
prohibit_assoc_item_constraint(self, c, 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 constraints are not handled here! They are either lowered via
/// `lower_assoc_item_constraint` or rejected via `prohibit_assoc_item_constraint`.
///
/// ### 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 item constraints like `Output = u32` are contained in `generic_args.constraints`.
///
/// 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>>,
) -> (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 arg_count = check_generic_arg_count(
self,
def_id,
segment,
generics,
GenericArgPosition::Type,
self_ty.is_some(),
);
// 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 item constraints will be handled regardless of whether there are
// any non-`Self` generic parameters.
if generics.is_own_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,
infer_args: bool,
incorrect_args: &'a Result<(), GenericArgCountMismatch>,
}
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,
preceding_args: &[ty::GenericArg<'tcx>],
param: &ty::GenericParamDef,
arg: &GenericArg<'tcx>,
) -> ty::GenericArg<'tcx> {
let tcx = self.lowerer.tcx();
if let Err(incorrect) = self.incorrect_args {
if incorrect.invalid_args.contains(&(param.index as usize)) {
return param.to_error(tcx);
}
}
let 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.
},
);
}
self.lowerer.lower_ty(ty).into()
};
match (&param.kind, arg) {
(GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
self.lowerer.lower_lifetime(lt, RegionInferReason::Param(param)).into()
}
(&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
// We handle the other parts of `Ty` in the match arm below
handle_ty_args(has_default, ty.as_unambig_ty())
}
(&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
handle_ty_args(has_default, &inf.to_ty())
}
(GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
.lowerer
// Ambig portions of `ConstArg` are handled in the match arm below
.lower_const_arg(
ct.as_unambig_ct(),
FeedConstTy::Param(param.def_id, preceding_args),
)
.into(),
(&GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
self.lowerer.ct_infer(Some(param), inf.span).into()
}
(kind, arg) => span_bug!(
self.span,
"mismatched path argument for kind {kind:?}: found arg {arg:?}"
),
}
}
fn inferred_kind(
&mut self,
preceding_args: &[ty::GenericArg<'tcx>],
param: &ty::GenericParamDef,
infer_args: bool,
) -> ty::GenericArg<'tcx> {
let tcx = self.lowerer.tcx();
if let Err(incorrect) = self.incorrect_args {
if incorrect.invalid_args.contains(&(param.index as usize)) {
return param.to_error(tcx);
}
}
match param.kind {
GenericParamDefKind::Lifetime => {
self.lowerer.re_infer(self.span, RegionInferReason::Param(param)).into()
}
GenericParamDefKind::Type { has_default, .. } => {
if !infer_args && has_default {
// No type parameter provided, but a default exists.
if let Some(prev) =
preceding_args.iter().find_map(|arg| match arg.kind() {
GenericArgKind::Type(ty) => ty.error_reported().err(),
_ => None,
})
{
// Avoid ICE #86756 when type error recovery goes awry.
return Ty::new_error(tcx, prev).into();
}
tcx.at(self.span)
.type_of(param.def_id)
.instantiate(tcx, preceding_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)
.instantiate(tcx, preceding_args);
if let Err(guar) = ty.error_reported() {
return ty::Const::new_error(tcx, guar).into();
}
if !infer_args && has_default {
tcx.const_param_default(param.def_id)
.instantiate(tcx, preceding_args)
.into()
} else if infer_args {
self.lowerer.ct_infer(Some(param), self.span).into()
} else {
// We've already errored above about the mismatch.
ty::Const::new_misc_error(tcx).into()
}
}
}
}
}
let mut args_ctx = GenericArgsCtxt {
lowerer: self,
def_id,
span,
generic_args: segment.args(),
infer_args: segment.infer_args,
incorrect_args: &arg_count.correct,
};
let args = lower_generic_args(
self,
def_id,
parent_args,
self_ty.is_some(),
self_ty,
&arg_count,
&mut args_ctx,
);
(args, arg_count)
}
#[instrument(level = "debug", skip(self))]
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> {
let (args, _) =
self.lower_generic_args_of_path(span, item_def_id, parent_args, item_segment, None);
if let Some(c) = item_segment.args().constraints.first() {
prohibit_assoc_item_constraint(self, c, 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,
)
}
/// 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 iff the trait reference contains associated item constraints.
///
/// ### 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 `Ty: Iterator` in the 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: hir::BoundConstness,
polarity: hir::BoundPolarity,
self_ty: Ty<'tcx>,
bounds: &mut Vec<(ty::Clause<'tcx>, Span)>,
predicate_filter: PredicateFilter,
) -> 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.report_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),
);
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_from_args(tcx, trait_def_id, generic_args),
bound_vars,
);
debug!(?poly_trait_ref);
let polarity = match polarity {
rustc_ast::BoundPolarity::Positive => ty::PredicatePolarity::Positive,
rustc_ast::BoundPolarity::Negative(_) => ty::PredicatePolarity::Negative,
rustc_ast::BoundPolarity::Maybe(_) => {
// Validate associated type at least. We may want to reject these
// outright in the future...
for constraint in trait_segment.args().constraints {
let _ = self.lower_assoc_item_constraint(
trait_ref.hir_ref_id,
poly_trait_ref,
constraint,
&mut Default::default(),
&mut Default::default(),
constraint.span,
predicate_filter,
);
}
return arg_count;
}
};
// We deal with const conditions later.
match predicate_filter {
PredicateFilter::All
| PredicateFilter::SelfOnly
| PredicateFilter::SelfTraitThatDefines(..)
| PredicateFilter::SelfAndAssociatedTypeBounds => {
let bound = poly_trait_ref.map_bound(|trait_ref| {
ty::ClauseKind::Trait(ty::TraitPredicate { trait_ref, polarity })
});
let bound = (bound.upcast(tcx), span);
// FIXME(-Znext-solver): We can likely remove this hack once the
// new trait solver lands. This fixed an overflow in the old solver.
// This may have performance implications, so please check perf when
// removing it.
// This was added in <https://github.com/rust-lang/rust/pull/123302>.
if tcx.is_lang_item(trait_def_id, rustc_hir::LangItem::Sized) {
bounds.insert(0, bound);
} else {
bounds.push(bound);
}
}
PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
}
if let hir::BoundConstness::Always(span) | hir::BoundConstness::Maybe(span) = constness
&& !self.tcx().is_const_trait(trait_def_id)
{
let (def_span, suggestion, suggestion_pre) =
match (trait_def_id.is_local(), self.tcx().sess.is_nightly_build()) {
(true, true) => (
None,
Some(tcx.def_span(trait_def_id).shrink_to_lo()),
if self.tcx().features().const_trait_impl() {
""
} else {
"enable `#![feature(const_trait_impl)]` in your crate and "
},
),
(false, _) | (_, false) => (Some(tcx.def_span(trait_def_id)), None, ""),
};
self.dcx().emit_err(crate::errors::ConstBoundForNonConstTrait {
span,
modifier: constness.as_str(),
def_span,
trait_name: self.tcx().def_path_str(trait_def_id),
suggestion_pre,
suggestion,
});
} else {
match predicate_filter {
// This is only concerned with trait predicates.
PredicateFilter::SelfTraitThatDefines(..) => {}
PredicateFilter::All
| PredicateFilter::SelfOnly
| PredicateFilter::SelfAndAssociatedTypeBounds => {
match constness {
hir::BoundConstness::Always(_) => {
if polarity == ty::PredicatePolarity::Positive {
bounds.push((
poly_trait_ref
.to_host_effect_clause(tcx, ty::BoundConstness::Const),
span,
));
}
}
hir::BoundConstness::Maybe(_) => {
// We don't emit a const bound here, since that would mean that we
// unconditionally need to prove a `HostEffect` predicate, even when
// the predicates are being instantiated in a non-const context. This
// is instead handled in the `const_conditions` query.
}
hir::BoundConstness::Never => {}
}
}
// On the flip side, when filtering `ConstIfConst` bounds, we only need to convert
// `[const]` bounds. All other predicates are handled in their respective queries.
//
// Note that like `PredicateFilter::SelfOnly`, we don't need to do any filtering
// here because we only call this on self bounds, and deal with the recursive case
// in `lower_assoc_item_constraint`.
PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {
match constness {
hir::BoundConstness::Maybe(_) => {
if polarity == ty::PredicatePolarity::Positive {
bounds.push((
poly_trait_ref
.to_host_effect_clause(tcx, ty::BoundConstness::Maybe),
span,
));
}
}
hir::BoundConstness::Always(_) | hir::BoundConstness::Never => {}
}
}
}
}
let mut dup_constraints = FxIndexMap::default();
for constraint in trait_segment.args().constraints {
// Don't register any associated item constraints for negative bounds,
// since we should have emitted an error for them earlier, and they
// would not be well-formed!
if polarity != ty::PredicatePolarity::Positive {
self.dcx().span_delayed_bug(
constraint.span,
"negative trait bounds should not have assoc item constraints",
);
break;
}
// Specify type to assert that error was already reported in `Err` case.
let _: Result<_, ErrorGuaranteed> = self.lower_assoc_item_constraint(
trait_ref.hir_ref_id,
poly_trait_ref,
constraint,
bounds,
&mut dup_constraints,
constraint.span,
predicate_filter,
);
// 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,
) -> ty::TraitRef<'tcx> {
self.report_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));
if let Some(c) = trait_segment.args().constraints.first() {
prohibit_assoc_item_constraint(self, c, Some((trait_def_id, trait_segment, span)));
}
ty::TraitRef::new_from_args(self.tcx(), trait_def_id, generic_args)
}
fn probe_trait_that_defines_assoc_item(
&self,
trait_def_id: DefId,
assoc_tag: ty::AssocTag,
assoc_ident: Ident,
) -> bool {
self.tcx()
.associated_items(trait_def_id)
.find_by_ident_and_kind(self.tcx(), assoc_ident, assoc_tag, 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_from_args(tcx, did, args);
Ty::new_alias(tcx, ty::Free, 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 item
/// given by `assoc_ident` and `kind`.
///
/// 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_item(
&self,
ty_param_def_id: LocalDefId,
ty_param_span: Span,
assoc_tag: ty::AssocTag,
assoc_ident: Ident,
span: Span,
) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
debug!(?ty_param_def_id, ?assoc_ident, ?span);
let tcx = self.tcx();
let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_ident);
debug!("predicates={:#?}", predicates);
self.probe_single_bound_for_assoc_item(
|| {
let trait_refs = predicates
.iter_identity_copied()
.filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref)));
traits::transitive_bounds_that_define_assoc_item(tcx, trait_refs, assoc_ident)
},
AssocItemQSelf::TyParam(ty_param_def_id, ty_param_span),
assoc_tag,
assoc_ident,
span,
None,
)
}
/// Search for a single trait bound whose trait defines the associated item given by
/// `assoc_ident`.
///
/// 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, qself, constraint), ret)]
fn probe_single_bound_for_assoc_item<I>(
&self,
all_candidates: impl Fn() -> I,
qself: AssocItemQSelf,
assoc_tag: ty::AssocTag,
assoc_ident: Ident,
span: Span,
constraint: Option<&hir::AssocItemConstraint<'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_tag, assoc_ident)
});
let Some(bound) = matching_candidates.next() else {
return Err(self.report_unresolved_assoc_item(
all_candidates,
qself,
assoc_tag,
assoc_ident,
span,
constraint,
));
};
debug!(?bound);
if let Some(bound2) = matching_candidates.next() {
debug!(?bound2);
let assoc_kind_str = errors::assoc_tag_str(assoc_tag);
let qself_str = qself.to_string(tcx);
let mut err = self.dcx().create_err(crate::errors::AmbiguousAssocItem {
span,
assoc_kind: assoc_kind_str,
assoc_ident,
qself: &qself_str,
});
// Provide a more specific error code index entry for equality bindings.
err.code(
if let Some(constraint) = constraint
&& let hir::AssocItemConstraintKind::Equality { .. } = constraint.kind
{
E0222
} else {
E0221
},
);
// FIXME(#97583): Print associated item bindings properly (i.e., not as equality
// predicates!).
// 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_ident_and_kind(tcx, assoc_ident, assoc_tag, 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_ident}` from `{}`", bound.print_trait_sugared(),),
);
if let Some(constraint) = constraint {
match constraint.kind {
hir::AssocItemConstraintKind::Equality { term } => {
let term: ty::Term<'_> = match term {
hir::Term::Ty(ty) => self.lower_ty(ty).into(),
hir::Term::Const(ct) => {
self.lower_const_arg(ct, FeedConstTy::No).into()
}
};
if term.references_error() {
continue;
}
// FIXME(#97583): This isn't syntactically well-formed!
where_bounds.push(format!(
" T: {trait}::{assoc_ident} = {term}",
trait = bound.print_only_trait_path(),
));
}
// FIXME: Provide a suggestion.
hir::AssocItemConstraintKind::Bound { bounds: _ } => {}
}
} else {
err.span_suggestion_verbose(
span.with_hi(assoc_ident.span.lo()),
"use fully-qualified syntax to disambiguate",
format!("<{qself_str} as {}>::", bound.print_only_trait_path()),
Applicability::MaybeIncorrect,
);
}
} else {
err.note(format!(
"associated {assoc_kind_str} `{assoc_ident}` 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: {qself_str},\n{}",
where_bounds.join(",\n"),
));
let reported = err.emit();
return Err(reported);
}
err.emit();
}
Ok(bound)
}
/// Lower a [type-relative](hir::QPath::TypeRelative) path in type position to a type.
///
/// 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 implementation 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.
///
/// [#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_type_relative_ty_path(
&self,
self_ty: Ty<'tcx>,
hir_self_ty: &'tcx hir::Ty<'tcx>,
segment: &'tcx hir::PathSegment<'tcx>,
qpath_hir_id: HirId,
span: Span,
permit_variants: PermitVariants,
) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
let tcx = self.tcx();
match self.lower_type_relative_path(
self_ty,
hir_self_ty,
segment,
qpath_hir_id,
span,
LowerTypeRelativePathMode::Type(permit_variants),
)? {
TypeRelativePath::AssocItem(def_id, args) => {
let alias_ty = ty::AliasTy::new_from_args(tcx, def_id, args);
let ty = Ty::new_alias(tcx, alias_ty.kind(tcx), alias_ty);
Ok((ty, tcx.def_kind(def_id), def_id))
}
TypeRelativePath::Variant { adt, variant_did } => {
Ok((adt, DefKind::Variant, variant_did))
}
}
}
/// Lower a [type-relative][hir::QPath::TypeRelative] path to a (type-level) constant.
#[instrument(level = "debug", skip_all, ret)]
fn lower_type_relative_const_path(
&self,
self_ty: Ty<'tcx>,
hir_self_ty: &'tcx hir::Ty<'tcx>,
segment: &'tcx hir::PathSegment<'tcx>,
qpath_hir_id: HirId,
span: Span,
) -> Result<Const<'tcx>, ErrorGuaranteed> {
let tcx = self.tcx();
let (def_id, args) = match self.lower_type_relative_path(
self_ty,
hir_self_ty,
segment,
qpath_hir_id,
span,
LowerTypeRelativePathMode::Const,
)? {
TypeRelativePath::AssocItem(def_id, args) => {
if !tcx.associated_item(def_id).is_type_const_capable(tcx) {
let mut err = self.dcx().struct_span_err(
span,
"use of trait associated const without `#[type_const]`",
);
err.note("the declaration in the trait must be marked with `#[type_const]`");
return Err(err.emit());
}
(def_id, args)
}
// FIXME(mgca): implement support for this once ready to support all adt ctor expressions,
// not just const ctors
TypeRelativePath::Variant { .. } => {
span_bug!(span, "unexpected variant res for type associated const path")
}
};
Ok(Const::new_unevaluated(tcx, ty::UnevaluatedConst::new(def_id, args)))
}
/// Lower a [type-relative][hir::QPath::TypeRelative] (and type-level) path.
#[instrument(level = "debug", skip_all, ret)]
fn lower_type_relative_path(
&self,
self_ty: Ty<'tcx>,
hir_self_ty: &'tcx hir::Ty<'tcx>,
segment: &'tcx hir::PathSegment<'tcx>,
qpath_hir_id: HirId,
span: Span,
mode: LowerTypeRelativePathMode,
) -> Result<TypeRelativePath<'tcx>, ErrorGuaranteed> {
debug!(%self_ty, ?segment.ident);
let tcx = self.tcx();
// Check if we have an enum variant or an inherent associated type.
let mut variant_def_id = None;
if let Some(adt_def) = self.probe_adt(span, self_ty) {
if adt_def.is_enum() {
let variant_def = adt_def
.variants()
.iter()
.find(|vd| tcx.hygienic_eq(segment.ident, vd.ident(tcx), adt_def.did()));
if let Some(variant_def) = variant_def {
if let PermitVariants::Yes = mode.permit_variants() {
tcx.check_stability(variant_def.def_id, Some(qpath_hir_id), span, None);
let _ = self.prohibit_generic_args(
slice::from_ref(segment).iter(),
GenericsArgsErrExtend::EnumVariant {
qself: hir_self_ty,
assoc_segment: segment,
adt_def,
},
);
return Ok(TypeRelativePath::Variant {
adt: self_ty,
variant_did: variant_def.def_id,
});
} else {
variant_def_id = Some(variant_def.def_id);
}
}
}
// FIXME(inherent_associated_types, #106719): Support self types other than ADTs.
if let Some((did, args)) = self.probe_inherent_assoc_item(
segment,
adt_def.did(),
self_ty,
qpath_hir_id,
span,
mode.assoc_tag(),
)? {
return Ok(TypeRelativePath::AssocItem(did, args));
}
}
let (item_def_id, bound) = self.resolve_type_relative_path(
self_ty,
hir_self_ty,
mode.assoc_tag(),
segment,
qpath_hir_id,
span,
variant_def_id,
)?;
let (item_def_id, args) = self.lower_assoc_item_path(span, item_def_id, segment, bound)?;
if let Some(variant_def_id) = variant_def_id {
tcx.node_span_lint(AMBIGUOUS_ASSOCIATED_ITEMS, qpath_hir_id, span, |lint| {
lint.primary_message("ambiguous associated item");
let mut could_refer_to = |kind: DefKind, def_id, also| {
let note_msg = format!(
"`{}` could{} refer to the {} defined here",
segment.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(mode.def_kind(), item_def_id, " also");
lint.span_suggestion(
span,
"use fully-qualified syntax",
format!(
"<{} as {}>::{}",
self_ty,
tcx.item_name(bound.def_id()),
segment.ident
),
Applicability::MachineApplicable,
);
});
}
Ok(TypeRelativePath::AssocItem(item_def_id, args))
}
/// Resolve a [type-relative](hir::QPath::TypeRelative) (and type-level) path.
fn resolve_type_relative_path(
&self,
self_ty: Ty<'tcx>,
hir_self_ty: &'tcx hir::Ty<'tcx>,
assoc_tag: ty::AssocTag,
segment: &'tcx hir::PathSegment<'tcx>,
qpath_hir_id: HirId,
span: Span,
variant_def_id: Option<DefId>,
) -> Result<(DefId, ty::PolyTraitRef<'tcx>), ErrorGuaranteed> {
let tcx = self.tcx();
let self_ty_res = match hir_self_ty.kind {
hir::TyKind::Path(hir::QPath::Resolved(_, path)) => path.res,
_ => Res::Err,
};
// Find the type of the assoc item, and the trait where the associated item is declared.
let bound = match (self_ty.kind(), self_ty_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.
self.dcx().span_bug(span, "expected cycle error");
};
self.probe_single_bound_for_assoc_item(
|| {
let trait_ref = ty::Binder::dummy(trait_ref.instantiate_identity());
traits::supertraits(tcx, trait_ref)
},
AssocItemQSelf::SelfTyAlias,
assoc_tag,
segment.ident,
span,
None,
)?
}
(
&ty::Param(_),
Res::SelfTyParam { trait_: param_did } | Res::Def(DefKind::TyParam, param_did),
) => self.probe_single_ty_param_bound_for_assoc_item(
param_did.expect_local(),
hir_self_ty.span,
assoc_tag,
segment.ident,
span,
)?,
_ => {
return Err(self.report_unresolved_type_relative_path(
self_ty,
hir_self_ty,
assoc_tag,
segment.ident,
qpath_hir_id,
span,
variant_def_id,
));
}
};
let assoc_item = self
.probe_assoc_item(segment.ident, assoc_tag, qpath_hir_id, span, bound.def_id())
.expect("failed to find associated item");
Ok((assoc_item.def_id, bound))
}
/// Search for inherent associated items for use at the type level.
fn probe_inherent_assoc_item(
&self,
segment: &hir::PathSegment<'tcx>,
adt_did: DefId,
self_ty: Ty<'tcx>,
block: HirId,
span: Span,
assoc_tag: ty::AssocTag,
) -> Result<Option<(DefId, GenericArgsRef<'tcx>)>, ErrorGuaranteed> {
let tcx = self.tcx();
if !tcx.features().inherent_associated_types() {
match assoc_tag {
// 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).
ty::AssocTag::Type => return Ok(None),
ty::AssocTag::Const => {
// We also gate the mgca codepath for type-level uses of inherent consts
// with the inherent_associated_types feature gate since it relies on the
// same machinery and has similar rough edges.
return Err(feature_err(
&tcx.sess,
sym::inherent_associated_types,
span,
"inherent associated types are unstable",
)
.emit());
}
ty::AssocTag::Fn => unreachable!(),
}
}
let name = segment.ident;
let candidates: Vec<_> = tcx
.inherent_impls(adt_did)
.iter()
.filter_map(|&impl_| {
let (item, scope) =
self.probe_assoc_item_unchecked(name, assoc_tag, block, impl_)?;
Some(InherentAssocCandidate { impl_, assoc_item: item.def_id, scope })
})
.collect();
let (applicable_candidates, fulfillment_errors) =
self.select_inherent_assoc_candidates(span, self_ty, candidates.clone());
let InherentAssocCandidate { impl_, assoc_item, scope: def_scope } =
match &applicable_candidates[..] {
&[] => Err(self.report_unresolved_inherent_assoc_item(
name,
self_ty,
candidates,
fulfillment_errors,
span,
assoc_tag,
)),
&[applicable_candidate] => Ok(applicable_candidate),
&[_, ..] => Err(self.report_ambiguous_inherent_assoc_item(
name,
candidates.into_iter().map(|cand| cand.assoc_item).collect(),
span,
)),
}?;
self.check_assoc_item(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())),
);
Ok(Some((assoc_item, args)))
}
/// Given name and kind search for the assoc item in the provided scope and check if it's accessible[^1].
///
/// [^1]: I.e., accessible in the provided scope wrt. visibility and stability.
fn probe_assoc_item(
&self,
ident: Ident,
assoc_tag: ty::AssocTag,
block: HirId,
span: Span,
scope: DefId,
) -> Option<ty::AssocItem> {
let (item, scope) = self.probe_assoc_item_unchecked(ident, assoc_tag, block, scope)?;
self.check_assoc_item(item.def_id, ident, scope, block, span);
Some(item)
}
/// Given name and kind search for the assoc item in the provided scope
/// *without* checking if it's accessible[^1].
///
/// [^1]: I.e., accessible in the provided scope wrt. visibility and stability.
fn probe_assoc_item_unchecked(
&self,
ident: Ident,
assoc_tag: ty::AssocTag,
block: HirId,
scope: DefId,
) -> Option<(ty::AssocItem, /*scope*/ DefId)> {
let tcx = self.tcx();
let (ident, def_scope) = tcx.adjust_ident_and_get_scope(ident, 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)
.filter_by_name_unhygienic(ident.name)
.find(|i| i.as_tag() == assoc_tag && i.ident(tcx).normalize_to_macros_2_0() == ident)?;
Some((*item, def_scope))
}
/// Check if the given assoc item is accessible in the provided scope wrt. visibility and stability.
fn check_assoc_item(
&self,
item_def_id: DefId,
ident: Ident,
scope: DefId,
block: HirId,
span: Span,
) {
let tcx = self.tcx();
if !tcx.visibility(item_def_id).is_accessible_from(scope, tcx) {
self.dcx().emit_err(crate::errors::AssocItemIsPrivate {
span,
kind: tcx.def_descr(item_def_id),
name: ident,
defined_here_label: tcx.def_span(item_def_id),
});
}
tcx.check_stability(item_def_id, 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(TypingMode::non_body_analysis());
&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.is_type()
&& !i.is_impl_trait_in_trait()
&& i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
})
// 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 header = tcx.impl_trait_header(impl_def_id).unwrap();
let trait_ref = header.trait_ref.instantiate(
tcx,
infcx.fresh_args_for_item(DUMMY_SP, impl_def_id),
);
let value = fold_regions(tcx, 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 [resolved][hir::QPath::Resolved] associated type path to a projection.
#[instrument(level = "debug", skip_all)]
fn lower_resolved_assoc_ty_path(
&self,
span: Span,
opt_self_ty: Option<Ty<'tcx>>,
item_def_id: DefId,
trait_segment: Option<&hir::PathSegment<'tcx>>,
item_segment: &hir::PathSegment<'tcx>,
) -> Ty<'tcx> {
match self.lower_resolved_assoc_item_path(
span,
opt_self_ty,
item_def_id,
trait_segment,
item_segment,
ty::AssocTag::Type,
) {
Ok((item_def_id, item_args)) => {
Ty::new_projection_from_args(self.tcx(), item_def_id, item_args)
}
Err(guar) => Ty::new_error(self.tcx(), guar),
}
}
/// Lower a [resolved][hir::QPath::Resolved] associated const path to a (type-level) constant.
#[instrument(level = "debug", skip_all)]
fn lower_resolved_assoc_const_path(
&self,
span: Span,
opt_self_ty: Option<Ty<'tcx>>,
item_def_id: DefId,
trait_segment: Option<&hir::PathSegment<'tcx>>,
item_segment: &hir::PathSegment<'tcx>,
) -> Const<'tcx> {
match self.lower_resolved_assoc_item_path(
span,
opt_self_ty,
item_def_id,
trait_segment,
item_segment,
ty::AssocTag::Const,
) {
Ok((item_def_id, item_args)) => {
let uv = ty::UnevaluatedConst::new(item_def_id, item_args);
Const::new_unevaluated(self.tcx(), uv)
}
Err(guar) => Const::new_error(self.tcx(), guar),
}
}
/// Lower a [resolved][hir::QPath::Resolved] (type-level) associated item path.
#[instrument(level = "debug", skip_all)]
fn lower_resolved_assoc_item_path(
&self,
span: Span,
opt_self_ty: Option<Ty<'tcx>>,
item_def_id: DefId,
trait_segment: Option<&hir::PathSegment<'tcx>>,
item_segment: &hir::PathSegment<'tcx>,
assoc_tag: ty::AssocTag,
) -> Result<(DefId, GenericArgsRef<'tcx>), ErrorGuaranteed> {
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 {
return Err(self.report_missing_self_ty_for_resolved_path(
trait_def_id,
span,
item_segment,
assoc_tag,
));
};
debug!(?self_ty);
let trait_ref =
self.lower_mono_trait_ref(span, trait_def_id, self_ty, trait_segment.unwrap(), false);
debug!(?trait_ref);
let item_args =
self.lower_generic_args_of_assoc_item(span, item_def_id, item_segment, trait_ref.args);
Ok((item_def_id, item_args))
}
pub fn prohibit_generic_args<'a>(
&self,
segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
err_extend: GenericsArgsErrExtend<'a>,
) -> 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_prohibited_generic_args(
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(c) = segment.args().constraints.first() {
return Err(prohibit_assoc_item_constraint(self, c, 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 [resolved][hir::QPath::Resolved] path to a type.
#[instrument(level = "debug", skip_all)]
pub fn lower_resolved_ty_path(
&self,
opt_self_ty: Option<Ty<'tcx>>,
path: &hir::Path<'tcx>,
hir_id: HirId,
permit_variants: PermitVariants,
) -> 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_matches!(tcx.opaque_ty_origin(did), hir::OpaqueTyOrigin::TyAlias { .. });
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 let PermitVariants::Yes = 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(&path.segments),
);
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::Param(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 = self.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();
Ty::new_error(tcx, reported)
} else {
ty
}
}
Res::Def(DefKind::AssocTy, def_id) => {
let trait_segment = if let [modules @ .., trait_, _item] = path.segments {
let _ = self.prohibit_generic_args(modules.iter(), GenericsArgsErrExtend::None);
Some(trait_)
} else {
None
};
self.lower_resolved_assoc_ty_path(
span,
opt_self_ty,
def_id,
trait_segment,
path.segments.last().unwrap(),
)
}
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");
Ty::new_error(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.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.to_def_id());
let br = ty::BoundTy {
var: ty::BoundVar::from_u32(index),
kind: ty::BoundTyKind::Param(def_id.to_def_id(), name),
};
Ty::new_bound(tcx, debruijn, br)
}
Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
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, param_def_id: DefId, path_hir_id: HirId) -> Const<'tcx> {
let tcx = self.tcx();
match tcx.named_bound_var(path_hir_id) {
Some(rbv::ResolvedArg::EarlyBound(_)) => {
// 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(param_def_id);
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&param_def_id];
let name = tcx.item_name(param_def_id);
ty::Const::new_param(tcx, ty::ParamConst::new(index, name))
}
Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
ty::Const::new_bound(tcx, debruijn, ty::BoundVar::from_u32(index))
}
Some(rbv::ResolvedArg::Error(guar)) => ty::Const::new_error(tcx, guar),
arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", path_hir_id),
}
}
/// Lower a [`hir::ConstArg`] to a (type-level) [`ty::Const`](Const).
#[instrument(skip(self), level = "debug")]
pub fn lower_const_arg(
&self,
const_arg: &hir::ConstArg<'tcx>,
feed: FeedConstTy<'_, 'tcx>,
) -> Const<'tcx> {
let tcx = self.tcx();
if let FeedConstTy::Param(param_def_id, args) = feed
&& let hir::ConstArgKind::Anon(anon) = &const_arg.kind
{
let anon_const_type = tcx.type_of(param_def_id).instantiate(tcx, args);
// FIXME(generic_const_parameter_types): Ideally we remove these errors below when
// we have the ability to intermix typeck of anon const const args with the parent
// bodies typeck.
// We also error if the type contains any regions as effectively any region will wind
// up as a region variable in mir borrowck. It would also be somewhat concerning if
// hir typeck was using equality but mir borrowck wound up using subtyping as that could
// result in a non-infer in hir typeck but a region variable in borrowck.
if tcx.features().generic_const_parameter_types()
&& (anon_const_type.has_free_regions() || anon_const_type.has_erased_regions())
{
let e = self.dcx().span_err(
const_arg.span(),
"anonymous constants with lifetimes in their type are not yet supported",
);
tcx.feed_anon_const_type(anon.def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, e)));
return ty::Const::new_error(tcx, e);
}
// We must error if the instantiated type has any inference variables as we will
// use this type to feed the `type_of` and query results must not contain inference
// variables otherwise we will ICE.
if anon_const_type.has_non_region_infer() {
let e = self.dcx().span_err(
const_arg.span(),
"anonymous constants with inferred types are not yet supported",
);
tcx.feed_anon_const_type(anon.def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, e)));
return ty::Const::new_error(tcx, e);
}
// We error when the type contains unsubstituted generics since we do not currently
// give the anon const any of the generics from the parent.
if anon_const_type.has_non_region_param() {
let e = self.dcx().span_err(
const_arg.span(),
"anonymous constants referencing generics are not yet supported",
);
tcx.feed_anon_const_type(anon.def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, e)));
return ty::Const::new_error(tcx, e);
}
tcx.feed_anon_const_type(
anon.def_id,
ty::EarlyBinder::bind(tcx.type_of(param_def_id).instantiate(tcx, args)),
);
}
let hir_id = const_arg.hir_id;
match const_arg.kind {
hir::ConstArgKind::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_resolved_const_path(opt_self_ty, path, hir_id)
}
hir::ConstArgKind::Path(hir::QPath::TypeRelative(hir_self_ty, segment)) => {
debug!(?hir_self_ty, ?segment);
let self_ty = self.lower_ty(hir_self_ty);
self.lower_type_relative_const_path(
self_ty,
hir_self_ty,
segment,
hir_id,
const_arg.span(),
)
.unwrap_or_else(|guar| Const::new_error(tcx, guar))
}
hir::ConstArgKind::Path(qpath @ hir::QPath::LangItem(..)) => {
ty::Const::new_error_with_message(
tcx,
qpath.span(),
format!("Const::lower_const_arg: invalid qpath {qpath:?}"),
)
}
hir::ConstArgKind::Anon(anon) => self.lower_anon_const(anon),
hir::ConstArgKind::Infer(span, ()) => self.ct_infer(None, span),
}
}
/// Lower a [resolved][hir::QPath::Resolved] path to a (type-level) constant.
fn lower_resolved_const_path(
&self,
opt_self_ty: Option<Ty<'tcx>>,
path: &hir::Path<'tcx>,
hir_id: HirId,
) -> Const<'tcx> {
let tcx = self.tcx();
let span = path.span;
match path.res {
Res::Def(DefKind::ConstParam, def_id) => {
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.iter(),
GenericsArgsErrExtend::Param(def_id),
);
self.lower_const_param(def_id, hir_id)
}
Res::Def(DefKind::Const | DefKind::Ctor(_, CtorKind::Const), did) => {
assert_eq!(opt_self_ty, None);
let _ = self.prohibit_generic_args(
path.segments.split_last().unwrap().1.iter(),
GenericsArgsErrExtend::None,
);
let args = self.lower_generic_args_of_path_segment(
span,
did,
path.segments.last().unwrap(),
);
ty::Const::new_unevaluated(tcx, ty::UnevaluatedConst::new(did, args))
}
Res::Def(DefKind::AssocConst, did) => {
let trait_segment = if let [modules @ .., trait_, _item] = path.segments {
let _ = self.prohibit_generic_args(modules.iter(), GenericsArgsErrExtend::None);
Some(trait_)
} else {
None
};
self.lower_resolved_assoc_const_path(
span,
opt_self_ty,
did,
trait_segment,
path.segments.last().unwrap(),
)
}
Res::Def(DefKind::Static { .. }, _) => {
span_bug!(span, "use of bare `static` ConstArgKind::Path's not yet supported")
}
// FIXME(const_generics): create real const to allow fn items as const paths
Res::Def(DefKind::Fn | DefKind::AssocFn, did) => {
self.dcx().span_delayed_bug(span, "function items cannot be used as const args");
let args = self.lower_generic_args_of_path_segment(
span,
did,
path.segments.last().unwrap(),
);
ty::Const::zero_sized(tcx, Ty::new_fn_def(tcx, did, args))
}
// Exhaustive match to be clear about what exactly we're considering to be
// an invalid Res for a const path.
res @ (Res::Def(
DefKind::Mod
| DefKind::Enum
| DefKind::Variant
| DefKind::Ctor(CtorOf::Variant, CtorKind::Fn)
| DefKind::Struct
| DefKind::Ctor(CtorOf::Struct, CtorKind::Fn)
| DefKind::OpaqueTy
| DefKind::TyAlias
| DefKind::TraitAlias
| DefKind::AssocTy
| DefKind::Union
| DefKind::Trait
| DefKind::ForeignTy
| DefKind::TyParam
| DefKind::Macro(_)
| DefKind::LifetimeParam
| DefKind::Use
| DefKind::ForeignMod
| DefKind::AnonConst
| DefKind::InlineConst
| DefKind::Field
| DefKind::Impl { .. }
| DefKind::Closure
| DefKind::ExternCrate
| DefKind::GlobalAsm
| DefKind::SyntheticCoroutineBody,
_,
)
| Res::PrimTy(_)
| Res::SelfTyParam { .. }
| Res::SelfTyAlias { .. }
| Res::SelfCtor(_)
| Res::Local(_)
| Res::ToolMod
| Res::NonMacroAttr(_)
| Res::Err) => Const::new_error_with_message(
tcx,
span,
format!("invalid Res {res:?} for const path"),
),
}
}
/// Literals are eagerly converted to a constant, everything else becomes `Unevaluated`.
#[instrument(skip(self), level = "debug")]
fn lower_anon_const(&self, anon: &AnonConst) -> Const<'tcx> {
let tcx = self.tcx();
let expr = &tcx.hir_body(anon.body).value;
debug!(?expr);
// FIXME(generic_const_parameter_types): We should use the proper generic args
// here. It's only used as a hint for literals so doesn't matter too much to use the right
// generic arguments, just weaker type inference.
let ty = tcx.type_of(anon.def_id).instantiate_identity();
match self.try_lower_anon_const_lit(ty, expr) {
Some(v) => v,
None => ty::Const::new_unevaluated(
tcx,
ty::UnevaluatedConst {
def: anon.def_id.to_def_id(),
args: ty::GenericArgs::identity_for_item(tcx, anon.def_id.to_def_id()),
},
),
}
}
#[instrument(skip(self), level = "debug")]
fn try_lower_anon_const_lit(
&self,
ty: Ty<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Option<Const<'tcx>> {
let tcx = self.tcx();
// Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
// currently have to be wrapped in curly brackets, so it's necessary to special-case.
let expr = match &expr.kind {
hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
block.expr.as_ref().unwrap()
}
_ => expr,
};
if let hir::ExprKind::Path(hir::QPath::Resolved(
_,
&hir::Path { res: Res::Def(DefKind::ConstParam, _), .. },
)) = expr.kind
{
span_bug!(
expr.span,
"try_lower_anon_const_lit: received const param which shouldn't be possible"
);
};
let lit_input = match expr.kind {
hir::ExprKind::Lit(lit) => Some(LitToConstInput { lit: lit.node, ty, neg: false }),
hir::ExprKind::Unary(hir::UnOp::Neg, expr) => match expr.kind {
hir::ExprKind::Lit(lit) => Some(LitToConstInput { lit: lit.node, ty, neg: true }),
_ => None,
},
_ => None,
};
lit_input
// Allow the `ty` to be an alias type, though we cannot handle it here, we just go through
// the more expensive anon const code path.
.filter(|l| !l.ty.has_aliases())
.map(|l| tcx.at(expr.span).lit_to_const(l))
}
fn lower_delegation_ty(&self, idx: hir::InferDelegationKind) -> Ty<'tcx> {
let delegation_sig = self.tcx().inherit_sig_for_delegation_item(self.item_def_id());
match idx {
hir::InferDelegationKind::Input(idx) => delegation_sig[idx],
hir::InferDelegationKind::Output => *delegation_sig.last().unwrap(),
}
}
/// Lower a type from the HIR to our internal notion of a type.
#[instrument(level = "debug", skip(self), ret)]
pub fn lower_ty(&self, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
let tcx = self.tcx();
let result_ty = match &hir_ty.kind {
hir::TyKind::InferDelegation(_, idx) => self.lower_delegation_ty(*idx),
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, RegionInferReason::Reference);
debug!(?r);
let t = self.lower_ty(mt.ty);
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::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.safety, bf.abi, bf.decl, None, Some(hir_ty)),
)
}
hir::TyKind::UnsafeBinder(binder) => Ty::new_unsafe_binder(
tcx,
ty::Binder::bind_with_vars(
self.lower_ty(binder.inner_ty),
tcx.late_bound_vars(hir_ty.hir_id),
),
),
hir::TyKind::TraitObject(bounds, tagged_ptr) => {
let lifetime = tagged_ptr.pointer();
let repr = tagged_ptr.tag();
if let Some(guar) = self.prohibit_or_lint_bare_trait_object_ty(hir_ty) {
// Don't continue with type analysis if the `dyn` keyword is missing
// It generates confusing errors, especially if the user meant to use another
// keyword like `impl`
Ty::new_error(tcx, guar)
} else {
let repr = match repr {
TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
};
self.lower_trait_object_ty(hir_ty.span, hir_ty.hir_id, bounds, lifetime, repr)
}
}
// If we encounter a fully qualified path with RTN generics, then it must have
// *not* gone through `lower_ty_maybe_return_type_notation`, and therefore
// it's certainly in an illegal position.
hir::TyKind::Path(hir::QPath::Resolved(_, path))
if path.segments.last().and_then(|segment| segment.args).is_some_and(|args| {
matches!(args.parenthesized, hir::GenericArgsParentheses::ReturnTypeNotation)
}) =>
{
let guar = self.dcx().emit_err(BadReturnTypeNotation { span: hir_ty.span });
Ty::new_error(tcx, guar)
}
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_resolved_ty_path(opt_self_ty, path, hir_ty.hir_id, PermitVariants::No)
}
&hir::TyKind::OpaqueDef(opaque_ty) => {
// 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 in_trait = match opaque_ty.origin {
hir::OpaqueTyOrigin::FnReturn {
in_trait_or_impl: Some(hir::RpitContext::Trait),
..
}
| hir::OpaqueTyOrigin::AsyncFn {
in_trait_or_impl: Some(hir::RpitContext::Trait),
..
} => true,
hir::OpaqueTyOrigin::FnReturn {
in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
..
}
| hir::OpaqueTyOrigin::AsyncFn {
in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
..
}
| hir::OpaqueTyOrigin::TyAlias { .. } => false,
};
self.lower_opaque_ty(opaque_ty.def_id, in_trait)
}
hir::TyKind::TraitAscription(hir_bounds) => {
// Impl trait in bindings lower as an infer var with additional
// set of type bounds.
let self_ty = self.ty_infer(None, hir_ty.span);
let mut bounds = Vec::new();
self.lower_bounds(
self_ty,
hir_bounds.iter(),
&mut bounds,
ty::List::empty(),
PredicateFilter::All,
);
self.register_trait_ascription_bounds(bounds, hir_ty.hir_id, hir_ty.span);
self_ty
}
// If we encounter a type relative path with RTN generics, then it must have
// *not* gone through `lower_ty_maybe_return_type_notation`, and therefore
// it's certainly in an illegal position.
hir::TyKind::Path(hir::QPath::TypeRelative(_, segment))
if segment.args.is_some_and(|args| {
matches!(args.parenthesized, hir::GenericArgsParentheses::ReturnTypeNotation)
}) =>
{
let guar = self.dcx().emit_err(BadReturnTypeNotation { span: hir_ty.span });
Ty::new_error(tcx, guar)
}
hir::TyKind::Path(hir::QPath::TypeRelative(hir_self_ty, segment)) => {
debug!(?hir_self_ty, ?segment);
let self_ty = self.lower_ty(hir_self_ty);
self.lower_type_relative_ty_path(
self_ty,
hir_self_ty,
segment,
hir_ty.hir_id,
hir_ty.span,
PermitVariants::No,
)
.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, span);
let (args, _) = self.lower_generic_args_of_path(
span,
def_id,
&[],
&hir::PathSegment::invalid(),
None,
);
tcx.at(span).type_of(def_id).instantiate(tcx, args)
}
hir::TyKind::Array(ty, length) => {
let length = self.lower_const_arg(length, FeedConstTy::No);
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_span = ty.span;
let ty = self.lower_ty(ty);
let pat_ty = match self.lower_pat_ty_pat(ty, ty_span, pat) {
Ok(kind) => Ty::new_pat(tcx, ty, tcx.mk_pat(kind)),
Err(guar) => Ty::new_error(tcx, guar),
};
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
}
fn lower_pat_ty_pat(
&self,
ty: Ty<'tcx>,
ty_span: Span,
pat: &hir::TyPat<'tcx>,
) -> Result<ty::PatternKind<'tcx>, ErrorGuaranteed> {
let tcx = self.tcx();
match pat.kind {
hir::TyPatKind::Range(start, end) => {
match ty.kind() {
// Keep this list of types in sync with the list of types that
// the `RangePattern` trait is implemented for.
ty::Int(_) | ty::Uint(_) | ty::Char => {
let start = self.lower_const_arg(start, FeedConstTy::No);
let end = self.lower_const_arg(end, FeedConstTy::No);
Ok(ty::PatternKind::Range { start, end })
}
_ => Err(self
.dcx()
.span_delayed_bug(ty_span, "invalid base type for range pattern")),
}
}
hir::TyPatKind::Or(patterns) => {
self.tcx()
.mk_patterns_from_iter(patterns.iter().map(|pat| {
self.lower_pat_ty_pat(ty, ty_span, pat).map(|pat| tcx.mk_pat(pat))
}))
.map(ty::PatternKind::Or)
}
hir::TyPatKind::Err(e) => Err(e),
}
}
/// Lower an opaque type (i.e., an existential impl-Trait type) from the HIR.
#[instrument(level = "debug", skip(self), ret)]
fn lower_opaque_ty(&self, def_id: LocalDefId, in_trait: bool) -> Ty<'tcx> {
let tcx = self.tcx();
let lifetimes = tcx.opaque_captured_lifetimes(def_id);
debug!(?lifetimes);
// 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(def_id).to_def_id()
} else {
def_id.to_def_id()
};
let generics = tcx.generics_of(def_id);
debug!(?generics);
// 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.
let offset = generics.count() - lifetimes.len();
let args = ty::GenericArgs::for_item(tcx, def_id, |param, _| {
if let Some(i) = (param.index as usize).checked_sub(offset) {
let (lifetime, _) = lifetimes[i];
self.lower_resolved_lifetime(lifetime).into()
} else {
tcx.mk_param_from_def(param)
}
});
debug!(?args);
if in_trait {
Ty::new_projection_from_args(tcx, def_id, args)
} else {
Ty::new_opaque(tcx, def_id, args)
}
}
/// Lower a function type from the HIR to our internal notion of a function signature.
#[instrument(level = "debug", skip(self, hir_id, safety, abi, decl, generics, hir_ty), ret)]
pub fn lower_fn_ty(
&self,
hir_id: HirId,
safety: hir::Safety,
abi: rustc_abi::ExternAbi,
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);
let (input_tys, output_ty) = self.lower_fn_sig(decl, generics, hir_id, hir_ty);
debug!(?output_ty);
let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, safety, abi);
let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
if let hir::Node::Ty(hir::Ty { kind: hir::TyKind::BareFn(bare_fn_ty), span, .. }) =
tcx.hir_node(hir_id)
{
check_abi(tcx, hir_id, *span, bare_fn_ty.abi);
}
// reject function types that violate cmse ABI requirements
cmse::validate_cmse_abi(self.tcx(), self.dcx(), hir_id, abi, bare_fn_ty);
if !bare_fn_ty.references_error() {
// 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!(
self.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.
pub(super) 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_ident_and_kind(
tcx,
*ident,
ty::AssocTag::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<'cx>(
&'cx self,
constrained_regions: FxIndexSet<ty::BoundRegionKind>,
referenced_regions: FxIndexSet<ty::BoundRegionKind>,
generate_err: impl Fn(&str) -> Diag<'cx>,
) {
for br in referenced_regions.difference(&constrained_regions) {
let br_name = match *br {
ty::BoundRegionKind::Named(_, kw::UnderscoreLifetime)
| ty::BoundRegionKind::Anon
| ty::BoundRegionKind::ClosureEnv => "an anonymous lifetime".to_string(),
ty::BoundRegionKind::Named(_, name) => format!("lifetime `{name}`"),
};
let mut err = generate_err(&br_name);
if let ty::BoundRegionKind::Named(_, kw::UnderscoreLifetime)
| ty::BoundRegionKind::Anon = *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");
}
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.dcx().emit_err(AmbiguousLifetimeBound { span });
}
Some(r)
}
}