tests: adds cargo fix tests

Co-Developed-by: Eric Holk
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

Author: vincenzopalazzo

tests/ui/macros/expr_2021_cargo_fix_edition.fixed

@@ -0,0 +1,19 @@
+//@ run-rustfix
+//@ check-pass
+//@ compile-flags: --edition=2021
+#![allow(incomplete_features)]
+#![feature(expr_fragment_specifier_2024)]
+#![warn(edition_2024_expr_fragment_specifier)]
+
+macro_rules! m {
+    ($e:expr_2021) => { //~ WARN: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+       //~^ WARN: this changes meaning in Rust 2024
+        $e
+    };
+    ($($i:expr_2021)*) => { }; //~ WARN: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+       //~^ WARN: this changes meaning in Rust 2024
+}
+
+fn main() {
+    m!(());
+}

tests/ui/macros/expr_2021_cargo_fix_edition.rs

@@ -0,0 +1,19 @@
+//@ run-rustfix
+//@ check-pass
+//@ compile-flags: --edition=2021
+#![allow(incomplete_features)]
+#![feature(expr_fragment_specifier_2024)]
+#![warn(edition_2024_expr_fragment_specifier)]
+
+macro_rules! m {
+    ($e:expr) => { //~ WARN: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+       //~^ WARN: this changes meaning in Rust 2024
+        $e
+    };
+    ($($i:expr)*) => { }; //~ WARN: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+       //~^ WARN: this changes meaning in Rust 2024
+}
+
+fn main() {
+    m!(());
+}

tests/ui/macros/expr_2021_cargo_fix_edition.stderr

@@ -0,0 +1,33 @@
+warning: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+  --> $DIR/expr_2021_cargo_fix_edition.rs:9:9
+   |
+LL |     ($e:expr) => {
+   |         ^^^^
+   |
+   = warning: this changes meaning in Rust 2024
+   = note: for more information, see Migration Guide <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/macro-fragment-specifiers.html>
+note: the lint level is defined here
+  --> $DIR/expr_2021_cargo_fix_edition.rs:6:9
+   |
+LL | #![warn(edition_2024_expr_fragment_specifier)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: to keep the existing behavior, use the `expr_2021` fragment specifier.
+   |
+LL |     ($e:expr_2021) => {
+   |         ~~~~~~~~~
+
+warning: the `expr` fragment specifier will accept more expressions in the 2024 edition.
+  --> $DIR/expr_2021_cargo_fix_edition.rs:13:11
+   |
+LL |     ($($i:expr)*) => { };
+   |           ^^^^
+   |
+   = warning: this changes meaning in Rust 2024
+   = note: for more information, see Migration Guide <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/macro-fragment-specifiers.html>
+help: to keep the existing behavior, use the `expr_2021` fragment specifier.
+   |
+LL |     ($($i:expr_2021)*) => { };
+   |           ~~~~~~~~~
+
+warning: 2 warnings emitted
+