Rollup merge of #122527 - fmease:clean-up-hir-ty-lowering, r=compiler-errors

Clean up AstConv

Split off from #120926 to make it only contain the renaming & (doc) comment updates.
Any changes other than that which have accumulated over time are now part of this PR.
Let's be disciplined ;) Inspired by https://github.com/rust-lang/rust/pull/120926#issuecomment-1997984483.

---

* Remove `hir_trait_to_predicates`
  * Unused since #113671
* Inline `create_args_for_ast_trait_ref`
  * Only had a single call site
  * Having it as a separate method didn't gain us anything
* Use an if-let guard somewhere to avoid unwrapping
* Avoid explicit trait object lifetimes
  * More legible, stylistic-only (the updated code is 100% semantically identical)
  * Use explicitly elided lifetimes in impl headers, they get elaborated to distinct lifetimes
  * Make use of [object lifetime defaulting](https://doc.rust-lang.org/reference/lifetime-elision.html#default-trait-object-lifetimes) for a trait object type inside of a reference type somewhere
* Use preexisting dedicated method `ItemCtxt::to_ty` over `<dyn AstConv<'_>>::ast_ty_to_ty`
* Use preexisting dedicated method `AstConv::astconv` over explicit coercions
* Simplify the function signature of `create_args_for_ast_path` and of `check_generic_arg_count`
  * In both cases redundant information was passed rendering the call sites verbose and confusing
  * No perf impact (tested in [#120926](https://github.com/rust-lang/rust/pull/120926))
* Move diagnostic method `report_ambiguous_associated_type` from `astconv` to `astconv::errors`
  * The submodule `errors` exists specifically for that purpose
  * Use it to keep the main module clean & short

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -22,7 +22,7 @@
 use rustc_span::{Span, Symbol, DUMMY_SP};
 use rustc_trait_selection::traits::object_safety_violations_for_assoc_item;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
     /// the type parameter's name as a placeholder.
     pub(crate) fn complain_about_missing_type_params(
@@ -349,6 +349,118 @@ fn complain_about_assoc_kind_mismatch(
         })
     }
 
+    pub(super) fn report_ambiguous_associated_type(
+        &self,
+        span: Span,
+        types: &[String],
+        traits: &[String],
+        name: Symbol,
+    ) -> ErrorGuaranteed {
+        let mut err =
+            struct_span_code_err!(self.tcx().dcx(), span, E0223, "ambiguous associated type");
+        if self
+            .tcx()
+            .resolutions(())
+            .confused_type_with_std_module
+            .keys()
+            .any(|full_span| full_span.contains(span))
+        {
+            err.span_suggestion_verbose(
+                span.shrink_to_lo(),
+                "you are looking for the module in `std`, not the primitive type",
+                "std::",
+                Applicability::MachineApplicable,
+            );
+        } else {
+            let mut types = types.to_vec();
+            types.sort();
+            let mut traits = traits.to_vec();
+            traits.sort();
+            match (&types[..], &traits[..]) {
+                ([], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a type named `Type` that implements a trait named \
+                             `Trait` with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        format!("<Type as Trait>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], [trait_str]) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a type named `Example` that implemented `{trait_str}`, \
+                             you could use the fully-qualified path",
+                        ),
+                        format!("<Example as {trait_str}>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], traits) => {
+                    err.span_suggestions(
+                        span,
+                        format!(
+                            "if there were a type named `Example` that implemented one of the \
+                             traits with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        traits
+                            .iter()
+                            .map(|trait_str| format!("<Example as {trait_str}>::{name}"))
+                            .collect::<Vec<_>>(),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([type_str], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for `{type_str}`, you could use the fully-qualified path",
+                        ),
+                        format!("<{type_str} as Example>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, []) => {
+                    err.span_suggestions(
+                        span,
+                        format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for one of the types, you could use the fully-qualified \
+                             path",
+                        ),
+                        types
+                            .into_iter()
+                            .map(|type_str| format!("<{type_str} as Example>::{name}")),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, traits) => {
+                    let mut suggestions = vec![];
+                    for type_str in types {
+                        for trait_str in traits {
+                            suggestions.push(format!("<{type_str} as {trait_str}>::{name}"));
+                        }
+                    }
+                    err.span_suggestions(
+                        span,
+                        "use fully-qualified syntax",
+                        suggestions,
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+        }
+        let reported = err.emit();
+        self.set_tainted_by_errors(reported);
+        reported
+    }
+
     pub(crate) fn complain_about_ambiguous_inherent_assoc_type(
         &self,
         name: Ident,

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -409,15 +409,12 @@ pub fn check_generic_arg_count_for_call(
     seg: &hir::PathSegment<'_>,
     is_method_call: IsMethodCall,
 ) -> GenericArgCountResult {
-    let empty_args = hir::GenericArgs::none();
-    let gen_args = seg.args.unwrap_or(&empty_args);
     let gen_pos = match is_method_call {
         IsMethodCall::Yes => GenericArgPosition::MethodCall,
         IsMethodCall::No => GenericArgPosition::Value,
     };
     let has_self = generics.parent.is_none() && generics.has_self;
-
+    check_generic_arg_count(tcx, def_id, seg, generics, gen_pos, has_self)
-    check_generic_arg_count(tcx, def_id, seg, generics, gen_args, gen_pos, has_self, seg.infer_args)
 }
 
 /// Checks that the correct number of generic arguments have been provided.
@@ -428,11 +425,10 @@ pub(crate) fn check_generic_arg_count(
     def_id: DefId,
     seg: &hir::PathSegment<'_>,
     gen_params: &ty::Generics,
-    gen_args: &hir::GenericArgs<'_>,
     gen_pos: GenericArgPosition,
     has_self: bool,
-    infer_args: bool,
 ) -> GenericArgCountResult {
+    let gen_args = seg.args();
     let default_counts = gen_params.own_defaults();
     let param_counts = gen_params.own_counts();
 
@@ -453,7 +449,7 @@ pub(crate) fn check_generic_arg_count(
         .count();
     let named_const_param_count = param_counts.consts - synth_const_param_count;
     let infer_lifetimes =
-        (gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();
+        (gen_pos != GenericArgPosition::Type || seg.infer_args) && !gen_args.has_lifetime_params();
 
     if gen_pos != GenericArgPosition::Type
         && let Some(b) = gen_args.bindings.first()
@@ -586,7 +582,7 @@ pub(crate) fn check_generic_arg_count(
     };
 
     let args_correct = {
-        let expected_min = if infer_args {
+        let expected_min = if seg.infer_args {
             0
         } else {
             param_counts.consts + named_type_param_count

compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -8,7 +8,7 @@
 
 use super::AstConv;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// Make sure that we are in the condition to suggest the blanket implementation.
     pub(super) fn maybe_lint_blanket_trait_impl<G: EmissionGuarantee>(
         &self,

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -214,7 +214,7 @@ fn inferred_kind(
     ) -> ty::GenericArg<'tcx>;
 }
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     #[instrument(level = "debug", skip(self), ret)]
     pub fn ast_region_to_region(
         &self,
@@ -284,8 +284,6 @@ pub fn ast_path_args_for_ty(
             def_id,
             &[],
             item_segment,
-            item_segment.args(),
-            item_segment.infer_args,
             None,
             ty::BoundConstness::NotConst,
         );
@@ -330,14 +328,12 @@ pub fn ast_path_args_for_ty(
     /// type itself: `['a]`. The returned `GenericArgsRef` concatenates these two
     /// lists: `[Vec<u8>, u8, 'a]`.
     #[instrument(level = "debug", skip(self, span), ret)]
-    fn create_args_for_ast_path<'a>(
+    fn create_args_for_ast_path(
         &self,
         span: Span,
         def_id: DefId,
         parent_args: &[ty::GenericArg<'tcx>],
-        seg: &hir::PathSegment<'_>,
+        segment: &hir::PathSegment<'tcx>,
-        generic_args: &'a hir::GenericArgs<'tcx>,
-        infer_args: bool,
         self_ty: Option<Ty<'tcx>>,
         constness: ty::BoundConstness,
     ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
@@ -365,12 +361,10 @@ fn create_args_for_ast_path<'a>(
         let mut arg_count = check_generic_arg_count(
             tcx,
             def_id,
-            seg,
+            segment,
             generics,
-            generic_args,
             GenericArgPosition::Type,
             self_ty.is_some(),
-            infer_args,
         );
 
         if let Err(err) = &arg_count.correct
@@ -388,7 +382,7 @@ fn create_args_for_ast_path<'a>(
         }
 
         struct InstantiationsForAstPathCtxt<'a, 'tcx> {
-            astconv: &'a (dyn AstConv<'tcx> + 'a),
+            astconv: &'a dyn AstConv<'tcx>,
             def_id: DefId,
             generic_args: &'a GenericArgs<'tcx>,
             span: Span,
@@ -547,9 +541,9 @@ fn inferred_kind(
             astconv: self,
             def_id,
             span,
-            generic_args,
+            generic_args: segment.args(),
             inferred_params: vec![],
-            infer_args,
+            infer_args: segment.infer_args,
         };
         if let ty::BoundConstness::Const | ty::BoundConstness::ConstIfConst = constness
             && generics.has_self
@@ -592,8 +586,6 @@ pub fn create_args_for_associated_item(
             item_def_id,
             parent_args,
             item_segment,
-            item_segment.args(),
-            item_segment.infer_args,
             None,
             ty::BoundConstness::NotConst,
         );
@@ -661,7 +653,6 @@ pub(crate) fn instantiate_poly_trait_ref(
     ) -> 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 args = trait_segment.args();
 
         self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
         self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
@@ -671,8 +662,6 @@ pub(crate) fn instantiate_poly_trait_ref(
             trait_def_id,
             &[],
             trait_segment,
-            args,
-            trait_segment.infer_args,
             Some(self_ty),
             constness,
         );
@@ -690,7 +679,7 @@ pub(crate) fn instantiate_poly_trait_ref(
         bounds.push_trait_bound(tcx, poly_trait_ref, span, polarity);
 
         let mut dup_bindings = FxIndexMap::default();
-        for binding in args.bindings {
+        for binding in trait_segment.args().bindings {
             // Don't register additional associated type bounds for negative bounds,
             // since we should have emitten an error for them earlier, and they will
             // not be well-formed!
@@ -729,12 +718,14 @@ fn ast_path_to_mono_trait_ref(
         // FIXME(effects) move all host param things in astconv to hir lowering
         constness: ty::BoundConstness,
     ) -> ty::TraitRef<'tcx> {
-        let (generic_args, _) = self.create_args_for_ast_trait_ref(
+        self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
+
+        let (generic_args, _) = self.create_args_for_ast_path(
             span,
             trait_def_id,
-            self_ty,
+            &[],
             trait_segment,
-            is_impl,
+            Some(self_ty),
             constness,
         );
         if let Some(b) = trait_segment.args().bindings.first() {
@@ -743,30 +734,6 @@ fn ast_path_to_mono_trait_ref(
         ty::TraitRef::new(self.tcx(), trait_def_id, generic_args)
     }
 
-    #[instrument(level = "debug", skip(self, span))]
-    fn create_args_for_ast_trait_ref<'a>(
-        &self,
-        span: Span,
-        trait_def_id: DefId,
-        self_ty: Ty<'tcx>,
-        trait_segment: &'a hir::PathSegment<'tcx>,
-        is_impl: bool,
-        constness: ty::BoundConstness,
-    ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
-        self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
-
-        self.create_args_for_ast_path(
-            span,
-            trait_def_id,
-            &[],
-            trait_segment,
-            trait_segment.args(),
-            trait_segment.infer_args,
-            Some(self_ty),
-            constness,
-        )
-    }
-
     fn trait_defines_associated_item_named(
         &self,
         trait_def_id: DefId,
@@ -801,115 +768,6 @@ fn ast_path_to_ty(
         }
     }
 
-    fn report_ambiguous_associated_type(
-        &self,
-        span: Span,
-        types: &[String],
-        traits: &[String],
-        name: Symbol,
-    ) -> ErrorGuaranteed {
-        let mut err =
-            struct_span_code_err!(self.tcx().dcx(), span, E0223, "ambiguous associated type");
-        if self
-            .tcx()
-            .resolutions(())
-            .confused_type_with_std_module
-            .keys()
-            .any(|full_span| full_span.contains(span))
-        {
-            err.span_suggestion_verbose(
-                span.shrink_to_lo(),
-                "you are looking for the module in `std`, not the primitive type",
-                "std::",
-                Applicability::MachineApplicable,
-            );
-        } else {
-            let mut types = types.to_vec();
-            types.sort();
-            let mut traits = traits.to_vec();
-            traits.sort();
-            match (&types[..], &traits[..]) {
-                ([], []) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a type named `Type` that implements a trait named \
-                             `Trait` with associated type `{name}`, you could use the \
-                             fully-qualified path",
-                        ),
-                        format!("<Type as Trait>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([], [trait_str]) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a type named `Example` that implemented `{trait_str}`, \
-                             you could use the fully-qualified path",
-                        ),
-                        format!("<Example as {trait_str}>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([], traits) => {
-                    err.span_suggestions(
-                        span,
-                        format!(
-                            "if there were a type named `Example` that implemented one of the \
-                             traits with associated type `{name}`, you could use the \
-                             fully-qualified path",
-                        ),
-                        traits.iter().map(|trait_str| format!("<Example as {trait_str}>::{name}")),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                ([type_str], []) => {
-                    err.span_suggestion_verbose(
-                        span,
-                        format!(
-                            "if there were a trait named `Example` with associated type `{name}` \
-                             implemented for `{type_str}`, you could use the fully-qualified path",
-                        ),
-                        format!("<{type_str} as Example>::{name}"),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                (types, []) => {
-                    err.span_suggestions(
-                        span,
-                        format!(
-                            "if there were a trait named `Example` with associated type `{name}` \
-                             implemented for one of the types, you could use the fully-qualified \
-                             path",
-                        ),
-                        types
-                            .into_iter()
-                            .map(|type_str| format!("<{type_str} as Example>::{name}")),
-                        Applicability::HasPlaceholders,
-                    );
-                }
-                (types, traits) => {
-                    let mut suggestions = vec![];
-                    for type_str in types {
-                        for trait_str in traits {
-                            suggestions.push(format!("<{type_str} as {trait_str}>::{name}"));
-                        }
-                    }
-                    err.span_suggestions(
-                        span,
-                        "use fully-qualified syntax",
-                        suggestions,
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
-        }
-        let reported = err.emit();
-        self.set_tainted_by_errors(reported);
-        reported
-    }
-
     // Search for a bound on a type parameter which includes the associated item
     // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
     // This function will fail if there are no suitable bounds or there is
@@ -2471,8 +2329,6 @@ fn ast_ty_to_ty_inner(
                     def_id,
                     &[],
                     &hir::PathSegment::invalid(),
-                    &GenericArgs::none(),
-                    true,
                     None,
                     ty::BoundConstness::NotConst,
                 );
@@ -2552,9 +2408,9 @@ fn impl_trait_ty_to_ty(
 
     pub fn ty_of_arg(&self, ty: &hir::Ty<'tcx>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
         match ty.kind {
-            hir::TyKind::Infer if expected_ty.is_some() => {
+            hir::TyKind::Infer if let Some(expected_ty) = expected_ty => {
-                self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
+                self.record_ty(ty.hir_id, expected_ty, ty.span);
-                expected_ty.unwrap()
+                expected_ty
             }
             _ => self.ast_ty_to_ty(ty),
         }

compiler/rustc_hir_analysis/src/astconv/object_safety.rs

@@ -17,7 +17,7 @@
 
 use super::AstConv;
 
-impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+impl<'tcx> dyn AstConv<'tcx> + '_ {
     pub(super) fn conv_object_ty_poly_trait_ref(
         &self,
         span: Span,

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -108,8 +108,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                 .unwrap()
                 .0
                 .def_id;
-            let item_ctxt = &ItemCtxt::new(tcx, item_def_id) as &dyn crate::astconv::AstConv<'_>;
+            let ty = ItemCtxt::new(tcx, item_def_id).to_ty(hir_ty);
-            let ty = item_ctxt.ast_ty_to_ty(hir_ty);
 
             // Iterate through the generics of the projection to find the one that corresponds to
             // the def_id that this query was called with. We filter to only type and const args here

compiler/rustc_hir_analysis/src/lib.rs

@@ -100,19 +100,16 @@
 
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_middle::middle;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_middle::util;
 use rustc_session::parse::feature_err;
-use rustc_span::{symbol::sym, Span, DUMMY_SP};
+use rustc_span::{symbol::sym, Span};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits;
 
-use astconv::{AstConv, OnlySelfBounds};
-use bounds::Bounds;
-use rustc_hir::def::DefKind;
-
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
@@ -222,31 +219,5 @@ pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx>
     // def-ID that will be used to determine the traits/predicates in
     // scope. This is derived from the enclosing item-like thing.
     let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
-    let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.def_id);
+    collect::ItemCtxt::new(tcx, env_def_id.def_id).to_ty(hir_ty)
-    item_cx.astconv().ast_ty_to_ty(hir_ty)
-}
-
-pub fn hir_trait_to_predicates<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    hir_trait: &hir::TraitRef<'tcx>,
-    self_ty: Ty<'tcx>,
-) -> Bounds<'tcx> {
-    // In case there are any projections, etc., find the "environment"
-    // def-ID that will be used to determine the traits/predicates in
-    // scope. This is derived from the enclosing item-like thing.
-    let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
-    let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.def_id);
-    let mut bounds = Bounds::default();
-    let _ = &item_cx.astconv().instantiate_poly_trait_ref(
-        hir_trait,
-        DUMMY_SP,
-        ty::BoundConstness::NotConst,
-        ty::ImplPolarity::Positive,
-        self_ty,
-        &mut bounds,
-        true,
-        OnlySelfBounds(false),
-    );
-
-    bounds
 }

compiler/rustc_hir_typeck/src/closure.rs

@@ -780,7 +780,7 @@ fn supplied_sig_of_closure(
         decl: &hir::FnDecl<'tcx>,
         closure_kind: hir::ClosureKind,
     ) -> ty::PolyFnSig<'tcx> {
-        let astconv: &dyn AstConv<'_> = self;
+        let astconv = self.astconv();
 
         trace!("decl = {:#?}", decl);
         debug!(?closure_kind);
@@ -985,7 +985,7 @@ fn error_sig_of_closure(
         decl: &hir::FnDecl<'tcx>,
         guar: ErrorGuaranteed,
     ) -> ty::PolyFnSig<'tcx> {
-        let astconv: &dyn AstConv<'_> = self;
+        let astconv = self.astconv();
         let err_ty = Ty::new_error(self.tcx, guar);
 
         let supplied_arguments = decl.inputs.iter().map(|a| {