From 994b58fee7e66c25d4b13a8a95feaff650088301 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 15 Apr 2024 10:45:37 -0400
Subject: [PATCH] Okay actually check only alias TYPES

---
 compiler/rustc_trait_selection/src/traits/wf.rs   | 12 +++---------
 tests/ui/higher-ranked/well-formed-aliases.rs     |  8 ++++++++
 tests/ui/higher-ranked/well-formed-aliases.stderr | 12 ++++++++++++
 3 files changed, 23 insertions(+), 9 deletions(-)
 create mode 100644 tests/ui/higher-ranked/well-formed-aliases.rs
 create mode 100644 tests/ui/higher-ranked/well-formed-aliases.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index f4189ff0902..57efd2996e4 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -435,12 +435,6 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         }
     }
 
-    /// Pushes the obligations required for an alias (except inherent) to be WF
-    /// into `self.out`.
-    fn compute_alias_ty(&mut self, data: ty::AliasTy<'tcx>) {
-        self.compute_alias_term(data.into());
-    }
-
     /// Pushes the obligations required for an alias (except inherent) to be WF
     /// into `self.out`.
     fn compute_alias_term(&mut self, data: ty::AliasTerm<'tcx>) {
@@ -498,7 +492,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
             self.out.extend(obligations);
         }
 
-        self.compute_projection_args(data.args);
+        data.args.visit_with(self);
     }
 
     fn compute_projection_args(&mut self, args: GenericArgsRef<'tcx>) {
@@ -702,8 +696,8 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
             }
 
             ty::Alias(ty::Projection | ty::Opaque | ty::Weak, data) => {
-                self.compute_alias_ty(data);
-                return; // Subtree handled by compute_projection.
+                let obligations = self.nominal_obligations(data.def_id, data.args);
+                self.out.extend(obligations);
             }
             ty::Alias(ty::Inherent, data) => {
                 self.compute_inherent_projection(data);
diff --git a/tests/ui/higher-ranked/well-formed-aliases.rs b/tests/ui/higher-ranked/well-formed-aliases.rs
new file mode 100644
index 00000000000..60e013a54bc
--- /dev/null
+++ b/tests/ui/higher-ranked/well-formed-aliases.rs
@@ -0,0 +1,8 @@
+trait Trait {
+    type Gat<U: ?Sized>;
+}
+
+fn test<T>(f: for<'a> fn(<&'a T as Trait>::Gat<&'a [str]>)) where for<'a> &'a T: Trait {}
+//~^ ERROR the size for values of type `str` cannot be known at compilation time
+
+fn main() {}
diff --git a/tests/ui/higher-ranked/well-formed-aliases.stderr b/tests/ui/higher-ranked/well-formed-aliases.stderr
new file mode 100644
index 00000000000..4a6f4e961d9
--- /dev/null
+++ b/tests/ui/higher-ranked/well-formed-aliases.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/well-formed-aliases.rs:5:52
+   |
+LL | fn test<T>(f: for<'a> fn(<&'a T as Trait>::Gat<&'a [str]>)) where for<'a> &'a T: Trait {}
+   |                                                    ^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: slice and array elements must have `Sized` type
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.