Add coverage for pat too

In 2021 pat was changed to recognize `|` at the top level, with
pat_param added to retain the old behavior. This means
pat is subject to the same cross-edition behavior as expr will be in
2024.

Co-authored-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

tests/ui/macros/auxiliary/metavar_2021.rs → tests/ui/macros/auxiliary/metavar_2018.rs

@@ -1,12 +1,14 @@
-//@ edition: 2021
+//@ edition: 2018
 #[macro_export]
 macro_rules! make_matcher {
     ($name:ident, $fragment_type:ident, $d:tt) => {
         #[macro_export]
         macro_rules! $name {
             ($d _:$fragment_type) => { true };
             (const { 0 }) => { false };
+            (A | B) => { false };
         }
     };
 }
-make_matcher!(is_expr_from_2021, expr, $);
+make_matcher!(is_expr_from_2018, expr, $);
+make_matcher!(is_pat_from_2018, pat, $);

tests/ui/macros/metavar_cross_edition_recursive_macros.rs

@@ -0,0 +1,41 @@
+//@ compile-flags: --edition=2024 -Z unstable-options
+//@ aux-build: metavar_2018.rs
+//@ run-pass
+
+// This test captures the behavior of macro-generating-macros with fragment
+// specifiers across edition boundaries.
+
+#![feature(expr_fragment_specifier_2024)]
+#![feature(macro_metavar_expr)]
+#![allow(incomplete_features)]
+
+extern crate metavar_2018;
+
+use metavar_2018::{is_expr_from_2018, is_pat_from_2018, make_matcher};
+
+make_matcher!(is_expr_from_2024, expr, $);
+make_matcher!(is_pat_from_2024, pat, $);
+
+fn main() {
+    // Check expr
+    let from_2018 = is_expr_from_2018!(const { 0 });
+    dbg!(from_2018);
+    let from_2024 = is_expr_from_2024!(const { 0 });
+    dbg!(from_2024);
+
+    // These capture the current, empirically determined behavior.
+    // It's not clear whether this is the desired behavior.
+    assert!(!from_2018);
+    assert!(!from_2024);
+
+    // Check pat
+    let from_2018 = is_pat_from_2018!(A | B);
+    dbg!(from_2018);
+    let from_2024 = is_pat_from_2024!(A | B);
+    dbg!(from_2024);
+
+    // These capture the current, empirically determined behavior.
+    // It's not clear whether this is the desired behavior.
+    assert!(!from_2018);
+    assert!(!from_2024);
+}