Add test for eager expanding of format_args

Author: HKalbasi

crates/hir-def/src/macro_expansion_tests/builtin_fn_macro.rs

@@ -235,6 +235,40 @@ fn main() {
     );
 }
 
+#[test]
+fn test_format_args_expand_eager() {
+    check(
+        r#"
+#[rustc_builtin_macro]
+macro_rules! concat {}
+
+#[rustc_builtin_macro]
+macro_rules! format_args {
+    ($fmt:expr) => ({ /* compiler built-in */ });
+    ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ })
+}
+
+fn main() {
+    format_args!(concat!("xxx{}y", "{:?}zzz"), 2, b);
+}
+"#,
+        expect![[r##"
+#[rustc_builtin_macro]
+macro_rules! concat {}
+
+#[rustc_builtin_macro]
+macro_rules! format_args {
+    ($fmt:expr) => ({ /* compiler built-in */ });
+    ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ })
+}
+
+fn main() {
+    $crate::fmt::Arguments::new_v1(&["xxx", "y", "zzz", ], &[$crate::fmt::ArgumentV1::new(&(2), $crate::fmt::Display::fmt), $crate::fmt::ArgumentV1::new(&(b), $crate::fmt::Debug::fmt), ]);
+}
+"##]],
+    );
+}
+
 #[test]
 fn test_format_args_expand_with_broken_member_access() {
     check(