Rollup merge of #143106 - yotamofek:pr/gce/non-local-ice, r=BoxyUwU

gce: don't ICE on non-local const

Fixes #133808

I have absolutely no idea what I'm doing here, but I followed `@BoxyUwU` 's [instructions](#133808 (comment)), and turns out this small change fixes #133808, and doesn't seem to break anything else.
(This code path is only reachable when the GCE feature gate is enabled, so even if it does break in a way that is not caught by current test coverage, I guess it's not as bad as breaking stable or non-incomplete features?)

Anyways, r? `@BoxyUwU` , if you don't mind.

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -421,7 +421,9 @@ fn const_evaluatable_predicates_of<'tcx>(
     impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ConstCollector<'tcx> {
         fn visit_const(&mut self, c: ty::Const<'tcx>) {
             if let ty::ConstKind::Unevaluated(uv) = c.kind() {
-                if is_const_param_default(self.tcx, uv.def.expect_local()) {
+                if let Some(local) = uv.def.as_local()
+                    && is_const_param_default(self.tcx, local)
+                {
                     // Do not look into const param defaults,
                     // these get checked when they are actually instantiated.
                     //

tests/crashes/133808.rs

@@ -0,0 +1,10 @@
+// regression test for #133808.
+
+#![feature(generic_const_exprs)]
+#![feature(min_generic_const_args)]
+#![allow(incomplete_features)]
+#![crate_type = "lib"]
+
+pub trait Foo {}
+impl Foo for [u8; std::path::MAIN_SEPARATOR] {}
+//~^ ERROR the constant `MAIN_SEPARATOR` is not of type `usize`

tests/ui/const-generics/generic_const_exprs/non-local-const.rs

@@ -0,0 +1,10 @@
+error: the constant `MAIN_SEPARATOR` is not of type `usize`
+  --> $DIR/non-local-const.rs:9:14
+   |
+LL | impl Foo for [u8; std::path::MAIN_SEPARATOR] {}
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `char`
+   |
+   = note: the length of array `[u8; MAIN_SEPARATOR]` must be type `usize`
+
+error: aborting due to 1 previous error
+