Add tests for nested macro_rules edition behavior

This adds tests to check the behavior of how nested macro_rules
definitions work across edition boundaries. This covers a change in
behavior due to rust-lang#133274.

See rust-lang#135669

Author: ehuss

tests/ui/editions/auxiliary/nested_macro_rules_dep_2021.rs

@@ -0,0 +1,23 @@
+//@ edition: 2021
+
+#[macro_export]
+macro_rules! make_macro_with_input {
+    ($i:ident) => {
+        macro_rules! macro_inner_input {
+            () => {
+                pub fn $i() {}
+            };
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! make_macro {
+    () => {
+        macro_rules! macro_inner {
+            () => {
+                pub fn gen() {}
+            };
+        }
+    };
+}

tests/ui/editions/auxiliary/nested_macro_rules_dep_2024.rs

@@ -0,0 +1,23 @@
+//@ edition: 2024
+
+#[macro_export]
+macro_rules! make_macro_with_input {
+    ($i:ident) => {
+        macro_rules! macro_inner_input {
+            () => {
+                pub fn $i() {}
+            };
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! make_macro {
+    () => {
+        macro_rules! macro_inner {
+            () => {
+                pub fn gen() {}
+            };
+        }
+    };
+}

tests/ui/editions/nested-macro-rules-edition-local-2021.rs

@@ -0,0 +1,30 @@
+// This checks the behavior of how nested macro_rules definitions are handled
+// with regards to edition spans. Prior to https://github.com/rust-lang/rust/pull/133274,
+// the compiler would compile the inner macro with the edition of the local crate.
+// Afterwards, it uses the edition where the macro was *defined*.
+//
+// Unfortunately macro_rules compiler discards the edition of any *input* that
+// was used to generate the macro. This is possibly not the behavior that we
+// want. If we want to keep with the philosophy that code should follow the
+// edition rules of the crate where it is written, then presumably we would
+// want the input tokens to retain the edition of where they were written.
+//
+// See https://github.com/rust-lang/rust/issues/135669 for more.
+
+//@ aux-crate: nested_macro_rules_dep_2024=nested_macro_rules_dep_2024.rs
+//@ edition:2024
+
+mod with_input {
+    // If we change the macro_rules input behavior, then this should pass
+    // because `gen` is written in a context with 2021 behavior.
+    nested_macro_rules_dep_2024::make_macro_with_input!{gen}
+    macro_inner_input!{}
+    //~^ ERROR found reserved keyword
+}
+mod no_input {
+    nested_macro_rules_dep_2024::make_macro!{}
+    macro_inner!{}
+    //~^ ERROR found reserved keyword
+}
+
+fn main() {}

tests/ui/editions/nested-macro-rules-edition-local-2021.stderr

@@ -0,0 +1,27 @@
+error: expected identifier, found reserved keyword `gen`
+  --> $DIR/nested-macro-rules-edition-local-2021.rs:21:5
+   |
+LL |     macro_inner_input!{}
+   |     ^^^^^^^^^^^^^^^^^^^^ expected identifier, found reserved keyword
+   |
+   = note: this error originates in the macro `macro_inner_input` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: escape `gen` to use it as an identifier
+   |
+LL |     nested_macro_rules_dep_2024::make_macro_with_input!{r#gen}
+   |                                                         ++
+
+error: expected identifier, found reserved keyword `gen`
+  --> $DIR/nested-macro-rules-edition-local-2021.rs:26:5
+   |
+LL |     macro_inner!{}
+   |     ^^^^^^^^^^^^^^ expected identifier, found reserved keyword
+   |
+   = note: this error originates in the macro `macro_inner` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: escape `gen` to use it as an identifier
+  --> $DIR/auxiliary/nested_macro_rules_dep_2024.rs:19:24
+   |
+LL |                 pub fn r#gen() {}
+   |                        ++
+
+error: aborting due to 2 previous errors
+

tests/ui/editions/nested-macro-rules-edition-local-2024.rs

@@ -0,0 +1,20 @@
+// See nested-macro-rules-edition-local-2021.rs for a description of this test.
+//
+// This flips the editions to show the opposite behavior.
+
+//@ aux-crate: nested_macro_rules_dep_2021=nested_macro_rules_dep_2021.rs
+//@ edition:2024
+//@ check-pass
+
+mod with_input {
+    // If we change the macro_rules input behavior, then this should fail
+    // because `gen` is written in a context with 2024 behavior.
+    nested_macro_rules_dep_2021::make_macro_with_input!{gen}
+    macro_inner_input!{}
+}
+mod no_input {
+    nested_macro_rules_dep_2021::make_macro!{}
+    macro_inner!{}
+}
+
+fn main() {}