Rollup merge of #129755 - vincenzopalazzo:macros/recursive-macros-between-edition, r=compiler-errors

test: cross-edition metavar fragment specifiers

There's a subtle interaction between macros with metavar expressions and the edition-dependent fragment matching behavior. This test illustrates the current behavior when using macro-generating-macros across crate boundaries with different editions.

See the original suggestion https://github.com/rust-lang/rust/pull/123865#discussion_r1577176199

Tracking:

- https://github.com/rust-lang/rust/issues/123742

tests/ui/macros/auxiliary/metavar_2018.rs

@@ -0,0 +1,14 @@
+//@ 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_2018, expr, $);
+make_matcher!(is_pat_from_2018, pat, $);

tests/ui/macros/metavar_cross_edition_recursive_macros.rs

@@ -0,0 +1,38 @@
+//@ compile-flags: --edition=2024 -Z unstable-options
+//@ aux-build: metavar_2018.rs
+//@ known-bug: #130484
+//@ 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);
+
+    assert!(!from_2018);
+    assert!(!from_2024); // from_2024 will be true once #130484 is fixed
+
+    // 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);
+
+    assert!(!from_2018);
+    assert!(!from_2024); // from_2024 will be true once #130484 is fixed
+}