Rollup merge of #113399 - compiler-errors:next-solver-byte-pat-again, r=oli-obk

Structurally normalize again for byte string lit pat checking

We need to structurally normalize the pointee of a match scrutinee when trying to match byte string patterns -- we used[^1] to call `structurally_resolve_type`, which errors for type vars[^2], but lcnr added `try_structurally_resolve_type`[^3] in the mean time, which is the right thing to use here since it's totally opportunistic.

Fixes rust-lang/trait-system-refactor-initiative#38

[^1]: #112428
[^2]: #112993
[^3]: #113086

compiler/rustc_hir_typeck/src/pat.rs

@@ -394,8 +394,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut pat_ty = ty;
         if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(..), .. }) = lt.kind {
             let expected = self.structurally_resolve_type(span, expected);
-            if let ty::Ref(_, inner_ty, _) = expected.kind()
-                && matches!(inner_ty.kind(), ty::Slice(_))
+            if let ty::Ref(_, inner_ty, _) = *expected.kind()
+                && self.try_structurally_resolve_type(span, inner_ty).is_slice()
             {
                 let tcx = self.tcx;
                 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");

tests/ui/traits/new-solver/slice-match-byte-lit.rs

@@ -1,5 +1,5 @@
 // compile-flags: -Ztrait-solver=next
-// known-bug: rust-lang/trait-system-refactor-initiative#38
+// check-pass
 
 fn test(s: &[u8]) {
     match &s[0..3] {

tests/ui/traits/new-solver/slice-match-byte-lit.stderr

@@ -1,11 +0,0 @@
-error[E0271]: type mismatch resolving `[u8; 3] <: <[u8] as Index<Range<usize>>>::Output`
-  --> $DIR/slice-match-byte-lit.rs:6:9
-   |
-LL |     match &s[0..3] {
-   |           -------- this expression has type `&<[u8] as Index<std::ops::Range<usize>>>::Output`
-LL |         b"uwu" => {}
-   |         ^^^^^^ types differ
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0271`.