Fix ICE while normalizing an infer type

Returning an error instead of triggering a debug_assertion
when a normalized type still has infer

Author: gurry

compiler/rustc_traits/src/normalize_erasing_regions.rs

@@ -41,9 +41,9 @@ fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<TyCtxt<'tcx>> + Par
             // fresh `InferCtxt`. If this assert does trigger, it will give
             // us a test case.
             debug_assert_eq!(normalized_value, resolved_value);
+
             let erased = infcx.tcx.erase_regions(resolved_value);
-            debug_assert!(!erased.has_infer(), "{erased:?}");
-            Ok(erased)
+            if !erased.has_infer() { Ok(erased) } else { Err(NoSolution) }
         }
         Err(NoSolution) => Err(NoSolution),
     }

tests/crashes/126942.rs

@@ -0,0 +1,22 @@
+// Regression test for #126942
+
+// Tests that we do not ICE when an attempt
+// is made to compute the layout of a type
+// that normalizes to an infer type
+
+struct Thing;
+
+pub trait Every {
+    type Assoc;
+}
+impl<T: ?Sized> Every for Thing {
+//~^ ERROR the type parameter `T` is not constrained by the impl trait, self type, or predicates
+    type Assoc = T;
+}
+
+ // The type of this static normalizes to `Infer`
+ // thanks to the `?Sized` constraint in the impl above
+static I: <Thing as Every>::Assoc = 3;
+//~^ ERROR type annotations needed
+
+fn main() {}

tests/ui/layout/ice-layout-of-invalid-type-126942.rs

@@ -0,0 +1,19 @@
+error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/ice-layout-of-invalid-type-126942.rs:12:6
+   |
+LL | impl<T: ?Sized> Every for Thing {
+   |      ^ unconstrained type parameter
+
+error[E0283]: type annotations needed
+  --> $DIR/ice-layout-of-invalid-type-126942.rs:19:11
+   |
+LL | static I: <Thing as Every>::Assoc = 3;
+   |           ^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T`
+   |
+   = note: cannot satisfy `_: Sync`
+   = note: shared static variables must have a type that implements `Sync`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0207, E0283.
+For more information about an error, try `rustc --explain E0207`.