Structurally normalize in range pattern checking in HIR typeck

Author: compiler-errors

compiler/rustc_hir_typeck/src/pat.rs

@@ -866,6 +866,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // be peeled to `str` while ty here is still `&str`, if we don't
                 // err early here, a rather confusing unification error will be
                 // emitted instead).
+                let ty = self.structurally_resolve_type(expr.span, ty);
                 let fail =
                     !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
                 Some((fail, ty, expr.span))

tests/ui/pattern/normalize-ty-in-range.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// Regression test for <https://github.com/rust-lang/trait-system-refactor-initiative/issues/200>.
+// Make sure we structurally normalize in range pattern checking in HIR typeck.
+
+trait Foo {
+    type Bar;
+}
+
+impl Foo for () {
+    type Bar = i32;
+}
+
+fn main() {
+    const X: <() as Foo>::Bar = 0;
+
+    match 0 {
+        X..=X => {}
+        _ => {}
+    }
+}