Rollup merge of rust-lang#89126 - FabianWolff:issue-89088, r=petrochenkov

Fix ICE when `indirect_structural_match` is allowed

Fixes rust-lang#89088. The ICE is caused by `delay_good_path_bug()`, which is called (indirectly) from a `format!()` macro invocation. I have moved the macro invocation into the `decorate` closure of `struct_span_lint_hir()`, so that the macro is only invoked if the lint is not allowed (i.e., causes at least a warning, and thus prevents `delay_good_path_bug()` from firing).

Author: the8472

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

@@ -322,16 +322,18 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                     && !self.saw_const_match_lint.get()
                 {
                     self.saw_const_match_lint.set(true);
-                    let msg = format!(
-                        "to use a constant of type `{}` in a pattern, \
-                        `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
-                        cv.ty, cv.ty,
-                    );
                     tcx.struct_span_lint_hir(
                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
                         id,
                         span,
-                        |lint| lint.build(&msg).emit(),
+                        |lint| {
+                            let msg = format!(
+                                "to use a constant of type `{}` in a pattern, \
+                                 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
+                                cv.ty, cv.ty,
+                            );
+                            lint.build(&msg).emit()
+                        },
                     );
                 }
                 // Since we are behind a reference, we can just bubble the error up so we get a

src/test/ui/consts/issue-89088.rs

@@ -0,0 +1,22 @@
+// Regression test for the ICE described in #89088.
+
+// check-pass
+
+#![allow(indirect_structural_match)]
+use std::borrow::Cow;
+
+const FOO: &A = &A::Field(Cow::Borrowed("foo"));
+
+#[derive(PartialEq, Eq)]
+enum A {
+    Field(Cow<'static, str>)
+}
+
+fn main() {
+    let var = A::Field(Cow::Borrowed("bar"));
+
+    match &var {
+        FOO => todo!(),
+        _ => todo!()
+    }
+}