Don't do intra-pass validation on MIR shims

compiler/rustc_mir_transform/src/shim.rs

@@ -90,7 +90,11 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
     };
     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 
-    pm::run_passes(
+    // We don't validate MIR here because the shims may generate code that's
+    // only valid in a reveal-all param-env. However, since we do initial
+    // validation with the MirBuilt phase, which uses a user-facing param-env.
+    // This causes validation errors when TAITs are involved.
+    pm::run_passes_no_validate(
         tcx,
         &mut result,
         &[

tests/ui/type-alias-impl-trait/auxiliary/drop-shim-relates-opaque-aux.rs

@@ -0,0 +1,21 @@
+// crate foo
+
+#![feature(type_alias_impl_trait)]
+
+type Tait = impl Sized;
+fn _constrain() -> Tait {}
+
+struct WrapperWithDrop<T>(T);
+impl<T> Drop for WrapperWithDrop<T> {
+    fn drop(&mut self) {}
+}
+
+pub struct Foo(WrapperWithDrop<Tait>);
+
+trait Id {
+    type Id: ?Sized;
+}
+impl<T: ?Sized> Id for T {
+    type Id = T;
+}
+pub struct Bar(WrapperWithDrop<<Tait as Id>::Id>);

tests/ui/type-alias-impl-trait/drop-shim-relates-opaque-issue-114375.rs

@@ -0,0 +1,10 @@
+// aux-build:drop-shim-relates-opaque-aux.rs
+// compile-flags: -Zvalidate-mir --crate-type=lib
+// build-pass
+
+extern crate drop_shim_relates_opaque_aux;
+
+pub fn drop_foo(_: drop_shim_relates_opaque_aux::Foo) {}
+pub fn drop_bar(_: drop_shim_relates_opaque_aux::Bar) {}
+
+fn main() {}