HIR ty lowering: Simplify signature of lower_poly_trait_ref

Author: fmease

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -482,12 +482,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
             match hir_bound {
                 hir::GenericBound::Trait(poly_trait_ref) => {
-                    let hir::TraitBoundModifiers { constness, polarity } = poly_trait_ref.modifiers;
                     let _ = self.lower_poly_trait_ref(
-                        &poly_trait_ref.trait_ref,
-                        poly_trait_ref.span,
-                        constness,
-                        polarity,
+                        poly_trait_ref,
                         param_ty,
                         bounds,
                         predicate_filter,

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -18,9 +18,7 @@ use tracing::{debug, instrument};
 
 use super::HirTyLowerer;
 use crate::errors::SelfInTypeAlias;
-use crate::hir_ty_lowering::{
-    GenericArgCountMismatch, GenericArgCountResult, PredicateFilter, RegionInferReason,
-};
+use crate::hir_ty_lowering::{GenericArgCountMismatch, PredicateFilter, RegionInferReason};
 
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// Lower a trait object type from the HIR to our internal notion of a type.
@@ -38,24 +36,18 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let mut user_written_bounds = Vec::new();
         let mut potential_assoc_types = Vec::new();
-        for trait_bound in hir_bounds.iter() {
-            if let hir::BoundPolarity::Maybe(_) = trait_bound.modifiers.polarity {
+        for poly_trait_ref in hir_bounds.iter() {
+            if let hir::BoundPolarity::Maybe(_) = poly_trait_ref.modifiers.polarity {
                 continue;
             }
-            if let GenericArgCountResult {
-                correct:
-                    Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
-                ..
-            } = self.lower_poly_trait_ref(
-                &trait_bound.trait_ref,
-                trait_bound.span,
-                hir::BoundConstness::Never,
-                hir::BoundPolarity::Positive,
+            let result = self.lower_poly_trait_ref(
+                poly_trait_ref,
                 dummy_self,
                 &mut user_written_bounds,
                 PredicateFilter::SelfOnly,
-            ) {
-                potential_assoc_types.extend(cur_potential_assoc_types);
+            );
+            if let Err(GenericArgCountMismatch { invalid_args, .. }) = result.correct {
+                potential_assoc_types.extend(invalid_args);
             }
         }
 

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -750,17 +750,20 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// 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))]
+    #[instrument(level = "debug", skip(self, bounds))]
     pub(crate) fn lower_poly_trait_ref(
         &self,
-        trait_ref: &hir::TraitRef<'tcx>,
-        span: Span,
-        constness: hir::BoundConstness,
-        polarity: hir::BoundPolarity,
+        poly_trait_ref: &hir::PolyTraitRef<'tcx>,
         self_ty: Ty<'tcx>,
         bounds: &mut Vec<(ty::Clause<'tcx>, Span)>,
         predicate_filter: PredicateFilter,
     ) -> GenericArgCountResult {
+        // We use the *resolved* bound vars later instead of the HIR ones since the former
+        // also include the bound vars of the overarching predicate if applicable.
+        let hir::PolyTraitRef { bound_generic_params: _, modifiers, ref trait_ref, span } =
+            *poly_trait_ref;
+        let hir::TraitBoundModifiers { constness, polarity } = modifiers;
+
         let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
         let trait_segment = trait_ref.path.segments.last().unwrap();
 

tests/ui/traits/const-traits/const-trait-bounds-trait-objects.rs

@@ -14,5 +14,7 @@ fn main() {
 trait NonConst {}
 const fn handle(_: &dyn const NonConst) {}
 //~^ ERROR const trait bounds are not allowed in trait object types
+//~| ERROR `const` can only be applied to `#[const_trait]` traits
 const fn take(_: &dyn [const] NonConst) {}
 //~^ ERROR `[const]` is not allowed here
+//~| ERROR `[const]` can only be applied to `#[const_trait]` traits

tests/ui/traits/const-traits/const-trait-bounds-trait-objects.stderr

@@ -19,12 +19,34 @@ LL | const fn handle(_: &dyn const NonConst) {}
    |                         ^^^^^^^^^^^^^^
 
 error: `[const]` is not allowed here
-  --> $DIR/const-trait-bounds-trait-objects.rs:17:19
+  --> $DIR/const-trait-bounds-trait-objects.rs:18:19
    |
 LL | const fn take(_: &dyn [const] NonConst) {}
    |                   ^^^^^^^^^^^
    |
    = note: trait objects cannot have `[const]` trait bounds
 
-error: aborting due to 4 previous errors
+error: `const` can only be applied to `#[const_trait]` traits
+  --> $DIR/const-trait-bounds-trait-objects.rs:15:25
+   |
+LL | const fn handle(_: &dyn const NonConst) {}
+   |                         ^^^^^ can't be applied to `NonConst`
+   |
+help: mark `NonConst` as `#[const_trait]` to allow it to have `const` implementations
+   |
+LL | #[const_trait] trait NonConst {}
+   | ++++++++++++++
+
+error: `[const]` can only be applied to `#[const_trait]` traits
+  --> $DIR/const-trait-bounds-trait-objects.rs:18:19
+   |
+LL | const fn take(_: &dyn [const] NonConst) {}
+   |                   ^^^^^^^^^^^ can't be applied to `NonConst`
+   |
+help: mark `NonConst` as `#[const_trait]` to allow it to have `const` implementations
+   |
+LL | #[const_trait] trait NonConst {}
+   | ++++++++++++++
+
+error: aborting due to 6 previous errors