Rollup merge of #111695 - fmease:dont-lump-together-alias-tys, r=compiler-errors

Exclude inherent projections from some alias type `match`es

Updating (hopefully) all remaining `match`es which I overlooked to update when adding `AliasKind::Inherent` in #109410.

Fixes #111399.
Sadly the regression test is a clippy test instead of a rustc one as I don't know of another way to test that a trait bound like `Ty::InhProj: Trait` doesn't cause a crash without reaching a cycle error first (this is getting old ^^').

`@rustbot` label F-inherent_associated_types
r? `@compiler-errors`

Author: Dylan-DPC

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -506,10 +506,12 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             | ty::Param(_)
             | ty::Placeholder(..)
             | ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
+            | ty::Alias(ty::Inherent, _)
             | ty::Error(_) => return,
             ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_))
             | ty::Bound(..) => bug!("unexpected self type for `{goal:?}`"),
-            ty::Alias(_, alias_ty) => alias_ty,
+            // Excluding IATs here as they don't have meaningful item bounds.
+            ty::Alias(ty::Projection | ty::Opaque, alias_ty) => alias_ty,
         };
 
         for assumption in self.tcx().item_bounds(alias_ty.def_id).subst(self.tcx(), alias_ty.substs)

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1543,7 +1543,10 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
     // Check whether the self-type is itself a projection.
     // If so, extract what we know from the trait and try to come up with a good answer.
     let bounds = match *obligation.predicate.self_ty().kind() {
-        ty::Alias(_, ref data) => tcx.item_bounds(data.def_id).subst(tcx, data.substs),
+        // Excluding IATs here as they don't have meaningful item bounds.
+        ty::Alias(ty::Projection | ty::Opaque, ref data) => {
+            tcx.item_bounds(data.def_id).subst(tcx, data.substs)
+        }
         ty::Infer(ty::TyVar(_)) => {
             // If the self-type is an inference variable, then it MAY wind up
             // being a projected type, so induce an ambiguity.

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -143,7 +143,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Before we go into the whole placeholder thing, just
         // quickly check if the self-type is a projection at all.
         match obligation.predicate.skip_binder().trait_ref.self_ty().kind() {
-            ty::Alias(..) => {}
+            // Excluding IATs here as they don't have meaningful item bounds.
+            ty::Alias(ty::Projection | ty::Opaque, _) => {}
             ty::Infer(ty::TyVar(_)) => {
                 span_bug!(
                     obligation.cause.span,

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -156,7 +156,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let placeholder_self_ty = placeholder_trait_predicate.self_ty();
         let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
         let (def_id, substs) = match *placeholder_self_ty.kind() {
-            ty::Alias(_, ty::AliasTy { def_id, substs, .. }) => (def_id, substs),
+            // Excluding IATs here as they don't have meaningful item bounds.
+            ty::Alias(ty::Projection | ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
+                (def_id, substs)
+            }
             _ => bug!("projection candidate for unexpected type: {:?}", placeholder_self_ty),
         };
 

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1645,7 +1645,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let tcx = self.infcx.tcx;
         let (def_id, substs) = match *placeholder_trait_predicate.trait_ref.self_ty().kind() {
-            ty::Alias(_, ty::AliasTy { def_id, substs, .. }) => (def_id, substs),
+            ty::Alias(ty::Projection | ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
+                (def_id, substs)
+            }
             _ => {
                 span_bug!(
                     obligation.cause.span,

src/tools/clippy/tests/ui/issue-111399.rs

@@ -0,0 +1,13 @@
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+// Check that rustc doesn't crash on the trait bound `Self::Ty: std::marker::Freeze`.
+
+pub struct Struct;
+
+impl Struct {
+    pub type Ty = usize;
+    pub const CT: Self::Ty = 42;
+}
+
+fn main() {}