Add fixme and test for issue #135289

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -1086,6 +1086,12 @@ fn find_fallback_pattern_typo<'tcx>(
                 let vis = cx.tcx.visibility(item.owner_id);
                 if vis.is_accessible_from(parent, cx.tcx) {
                     accessible.push(item_name);
+                    // FIXME: the line below from PR #135310 is a workaround for the ICE in issue
+                    // #135289, where a macro in a dependency can create unreachable patterns in the
+                    // current crate. Path trimming expects diagnostics for a typoed const, but no
+                    // diagnostics are emitted and we ICE. See
+                    // `tests/ui/resolve/const-with-typo-in-pattern-binding-ice-135289.rs` for a
+                    // test that reproduces the ICE if we don't use `with_no_trimmed_paths!`.
                     let path = with_no_trimmed_paths!(cx.tcx.def_path_str(item.owner_id));
                     accessible_path.push(path);
                 } else if name == item_name {

tests/ui/resolve/auxiliary/fake_matches.rs

@@ -0,0 +1,13 @@
+// Helper for test tests/ui/resolve/const-with-typo-in-pattern-binding-ice-135289.rs
+
+//@ edition: 2018
+
+#[macro_export]
+macro_rules! assert_matches {
+    ( $e:expr , $($pat:pat)|+ ) => {
+        match $e {
+            $($pat)|+ => (),
+            _ => (),
+        }
+    };
+}

tests/ui/resolve/const-with-typo-in-pattern-binding-ice-135289.rs

@@ -0,0 +1,17 @@
+// This is a non-regression test for issue 135289, where the "const with typo in pattern" diagnostic
+// caused an ICE when unexpectedly pretty printing a type for unreachable arms via a macro defined
+// in a dependency.
+
+#![warn(unreachable_patterns)] // needed to reproduce the ICE described in #135289
+
+//@ check-pass
+//@ aux-build: fake_matches.rs
+extern crate fake_matches;
+
+const _A: u64 = 0;
+pub fn f() -> u64 {
+    0
+}
+fn main() {
+    fake_matches::assert_matches!(f(), _non_existent);
+}