Unrolled build for rust-lang#140218

Rollup merge of rust-lang#140218 - fmease:hirtylo-clean-up-path-low, r=compiler-errors

HIR ty lowering: Clean up & refactor the lowering of type-relative paths

While rebasing rust-lang#126651 I realized that HIR ty lowering could benefit from some *spring cleaning* now that it's been extended to handle RTN and mGCA paths.

More seriously, similar to my merged PR rust-lang#118668 which unified the handling of all *associated item constraints* (assoc ty, const (ACE) & fn (RTN)), this PR (commit rust-lang@695fcf5) partially[^1] deduplicates the resolution code for all *type-relative paths* (assoc ty, const (mGCA) & fn (RTN)).

**Why**? DRY'ing that part of the code means PR rust-lang#126651 will automatically support RTN paths like `Ty::AssocTy::assoc_fn(..)` and it also implies shared diagnostic code and thus better diagnostics for RTN.

---

The other commits represent cleanups, renamings, moves. More notably, I've renamed path lowering methods to be a lot more descriptive, so ones lowering `QPath(Resolved)` paths now have `_resolved_` in their name and ones lowering `QPath(TypeRelative)` paths now have `_type_relative_` in their name. This should make it stupidly obvious what their purpose is.

---

Best reviewed commit by commit. The changes are close to trivial but the diff might make it look hairier.
r? compiler-errors

[^1]: Sadly, I couldn't unify as much compared to the other PR without introducing unnecessary `unreachable!()`s or rendering the code otherwise illegible with flags and micro helper traits.

Author: rust-timer

compiler/rustc_hir_analysis/messages.ftl

@@ -37,7 +37,7 @@ hir_analysis_assoc_kind_mismatch = expected {$expected}, found {$got}
 
 hir_analysis_assoc_kind_mismatch_wrap_in_braces_sugg = consider adding braces here
 
-hir_analysis_associated_type_trait_uninferred_generic_params = cannot use the associated {$what} of a trait with uninferred generic parameters
+hir_analysis_associated_type_trait_uninferred_generic_params = cannot use the {$what} of a trait with uninferred generic parameters
     .suggestion = use a fully qualified path with inferred lifetimes
 
 hir_analysis_associated_type_trait_uninferred_generic_params_multipart_suggestion = use a fully qualified path with explicit lifetimes

compiler/rustc_hir_analysis/src/collect.rs

@@ -44,7 +44,6 @@ use rustc_trait_selection::traits::ObligationCtxt;
 use tracing::{debug, instrument};
 
 use crate::errors;
-use crate::hir_ty_lowering::errors::assoc_tag_str;
 use crate::hir_ty_lowering::{FeedConstTy, HirTyLowerer, RegionInferReason};
 
 pub(crate) mod dump;
@@ -444,13 +443,12 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_ident))
     }
 
-    fn lower_assoc_shared(
+    fn lower_assoc_item_path(
         &self,
         span: Span,
         item_def_id: DefId,
         item_segment: &rustc_hir::PathSegment<'tcx>,
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
-        assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, ty::GenericArgsRef<'tcx>), ErrorGuaranteed> {
         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
             let item_args = self.lowerer().lower_generic_args_of_assoc_item(
@@ -525,7 +523,7 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
                 inferred_sugg,
                 bound,
                 mpart_sugg,
-                what: assoc_tag_str(assoc_tag),
+                what: self.tcx.def_descr(item_def_id),
             }))
         }
     }

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -4,9 +4,9 @@ use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
+use rustc_hir::AmbigArg;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_hir::{AmbigArg, HirId};
 use rustc_middle::bug;
 use rustc_middle::ty::{
     self as ty, IsSuggestable, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable, TypeVisitable,
@@ -309,7 +309,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     false => "`?Sized`",
                 };
                 // There was a `?Trait` bound, but it was neither `?Sized` nor `experimental_default_bounds`.
-                tcx.dcx().span_err(
+                self.dcx().span_err(
                     unbound.span,
                     format!(
                         "relaxing a default bound only does something for {}; \
@@ -675,7 +675,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
                 // Good error for `where Trait::method(..): Send`.
                 let Some(self_ty) = opt_self_ty else {
-                    let guar = self.error_missing_qpath_self_ty(
+                    let guar = self.report_missing_self_ty_for_resolved_path(
                         trait_def_id,
                         hir_ty.span,
                         item_segment,
@@ -713,120 +713,51 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     Err(guar) => Ty::new_error(tcx, guar),
                 }
             }
-            hir::QPath::TypeRelative(qself, item_segment)
-                if item_segment.args.is_some_and(|args| {
+            hir::QPath::TypeRelative(hir_self_ty, segment)
+                if segment.args.is_some_and(|args| {
                     matches!(args.parenthesized, hir::GenericArgsParentheses::ReturnTypeNotation)
                 }) =>
             {
-                match self
-                    .resolve_type_relative_return_type_notation(
-                        qself,
-                        item_segment,
-                        hir_ty.hir_id,
-                        hir_ty.span,
-                    )
-                    .and_then(|(candidate, item_def_id)| {
-                        self.lower_return_type_notation_ty(candidate, item_def_id, hir_ty.span)
-                    }) {
-                    Ok(ty) => Ty::new_alias(tcx, ty::Projection, ty),
-                    Err(guar) => Ty::new_error(tcx, guar),
-                }
-            }
-            _ => self.lower_ty(hir_ty),
-        }
-    }
-
-    /// Perform type-dependent lookup for a *method* for return type notation.
-    /// This generally mirrors `<dyn HirTyLowerer>::lower_assoc_path`.
-    fn resolve_type_relative_return_type_notation(
-        &self,
-        qself: &'tcx hir::Ty<'tcx>,
-        item_segment: &'tcx hir::PathSegment<'tcx>,
-        qpath_hir_id: HirId,
-        span: Span,
-    ) -> Result<(ty::PolyTraitRef<'tcx>, DefId), ErrorGuaranteed> {
-        let tcx = self.tcx();
-        let qself_ty = self.lower_ty(qself);
-        let assoc_ident = item_segment.ident;
-        let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = &qself.kind {
-            path.res
-        } else {
-            Res::Err
-        };
-
-        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.
-                    self.dcx().span_bug(span, "expected cycle error");
-                };
-
-                self.probe_single_bound_for_assoc_item(
-                    || {
-                        traits::supertraits(
-                            tcx,
-                            ty::Binder::dummy(trait_ref.instantiate_identity()),
-                        )
-                    },
-                    AssocItemQSelf::SelfTyAlias,
+                let self_ty = self.lower_ty(hir_self_ty);
+                let (item_def_id, bound) = match self.resolve_type_relative_path(
+                    self_ty,
+                    hir_self_ty,
                     ty::AssocTag::Fn,
-                    assoc_ident,
-                    span,
+                    segment,
+                    hir_ty.hir_id,
+                    hir_ty.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(),
-                qself.span,
-                ty::AssocTag::Fn,
-                assoc_ident,
-                span,
-            )?,
-            _ => {
-                if let Err(reported) = qself_ty.error_reported() {
-                    return Err(reported);
-                } else {
-                    // FIXME(return_type_notation): Provide some structured suggestion here.
-                    let err = struct_span_code_err!(
-                        self.dcx(),
-                        span,
-                        E0223,
-                        "ambiguous associated function"
+                ) {
+                    Ok(result) => result,
+                    Err(guar) => return Ty::new_error(tcx, guar),
+                };
+
+                // Don't let `T::method` resolve to some `for<'a> <T as Tr<'a>>::method`,
+                // which may happen via a higher-ranked where clause or supertrait.
+                // This is the same restrictions as associated types; even though we could
+                // support it, it just makes things a lot more difficult to support in
+                // `resolve_bound_vars`, since we'd need to introduce those as elided
+                // bound vars on the where clause too.
+                if bound.has_bound_vars() {
+                    return Ty::new_error(
+                        tcx,
+                        self.dcx().emit_err(errors::AssociatedItemTraitUninferredGenericParams {
+                            span: hir_ty.span,
+                            inferred_sugg: Some(hir_ty.span.with_hi(segment.ident.span.lo())),
+                            bound: format!("{}::", tcx.anonymize_bound_vars(bound).skip_binder()),
+                            mpart_sugg: None,
+                            what: tcx.def_descr(item_def_id),
+                        }),
                     );
-                    return Err(err.emit());
                 }
-            }
-        };
 
-        // Don't let `T::method` resolve to some `for<'a> <T as Tr<'a>>::method`,
-        // which may happen via a higher-ranked where clause or supertrait.
-        // This is the same restrictions as associated types; even though we could
-        // support it, it just makes things a lot more difficult to support in
-        // `resolve_bound_vars`, since we'd need to introduce those as elided
-        // bound vars on the where clause too.
-        if bound.has_bound_vars() {
-            return Err(self.tcx().dcx().emit_err(
-                errors::AssociatedItemTraitUninferredGenericParams {
-                    span,
-                    inferred_sugg: Some(span.with_hi(item_segment.ident.span.lo())),
-                    bound: format!("{}::", tcx.anonymize_bound_vars(bound).skip_binder(),),
-                    mpart_sugg: None,
-                    what: "function",
-                },
-            ));
+                match self.lower_return_type_notation_ty(bound, item_def_id, hir_ty.span) {
+                    Ok(ty) => Ty::new_alias(tcx, ty::Projection, ty),
+                    Err(guar) => Ty::new_error(tcx, guar),
+                }
+            }
+            _ => self.lower_ty(hir_ty),
         }
-
-        let trait_def_id = bound.def_id();
-        let assoc_ty = self
-            .probe_assoc_item(assoc_ident, ty::AssocTag::Fn, qpath_hir_id, span, trait_def_id)
-            .expect("failed to find associated type");
-
-        Ok((bound, assoc_ty.def_id))
     }
 
     /// Do the common parts of lowering an RTN type. This involves extending the

compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs

@@ -35,7 +35,7 @@ pub(crate) fn validate_cmse_abi<'tcx>(
                     _ => tcx.hir_span(hir_id),
                 };
                 struct_span_code_err!(
-                    tcx.dcx(),
+                    dcx,
                     span,
                     E0781,
                     "the `\"C-cmse-nonsecure-call\"` ABI is only allowed on function pointers"

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -78,15 +78,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         // We  don't support empty trait objects.
         if regular_traits.is_empty() && auto_traits.is_empty() {
-            let guar = self.report_trait_object_with_no_traits_error(
-                span,
-                user_written_bounds.iter().copied(),
-            );
+            let guar =
+                self.report_trait_object_with_no_traits(span, user_written_bounds.iter().copied());
             return Ty::new_error(tcx, guar);
         }
         // We don't support >1 principal
         if regular_traits.len() > 1 {
-            let guar = self.report_trait_object_addition_traits_error(&regular_traits);
+            let guar = self.report_trait_object_addition_traits(&regular_traits);
             return Ty::new_error(tcx, guar);
         }
         // Don't create a dyn trait if we have errors in the principal.
@@ -132,7 +130,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     if references_self {
                         // With trait alias and type alias combined, type resolver
                         // may not be able to catch all illegal `Self` usages (issue 139082)
-                        let guar = tcx.dcx().emit_err(SelfInTypeAlias { span });
+                        let guar = self.dcx().emit_err(SelfInTypeAlias { span });
                         b.term = replace_dummy_self_with_error(tcx, b.term, guar);
                     }
                 }
@@ -360,7 +358,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
                         && hir_bound.span.contains(span)
                 });
-                self.complain_about_missing_type_params(
+                self.report_missing_type_params(
                     missing_type_params,
                     trait_ref.def_id,
                     span,