Auto merge of #16048 - Veykril:concat-bytes-fix, r=Veykril

fix: Fix concat_bytes! expansion emitting an identifier

Fixes https://github.com/rust-lang/rust-analyzer/issues/16046 (note that this has always been broken)

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

@@ -468,12 +468,12 @@ macro_rules! concat_bytes {}
 
 fn main() { concat_bytes!(b'A', b"BC", [68, b'E', 70]); }
 "##,
-        expect![[r##"
+        expect![[r#"
 #[rustc_builtin_macro]
 macro_rules! concat_bytes {}
 
 fn main() { [b'A', 66, 67, 68, b'E', 70]; }
-"##]],
+"#]],
     );
 }
 

crates/hir-def/src/macro_expansion_tests/mbe/regression.rs

@@ -1004,3 +1004,29 @@ fn main() {
 "##]],
     );
 }
+
+#[test]
+fn eager_concat_bytes_panic() {
+    check(
+        r#"
+#[rustc_builtin_macro]
+#[macro_export]
+macro_rules! concat_bytes {}
+
+fn main() {
+    let x = concat_bytes!(2);
+}
+
+"#,
+        expect![[r#"
+#[rustc_builtin_macro]
+#[macro_export]
+macro_rules! concat_bytes {}
+
+fn main() {
+    let x = /* error: unexpected token in input */[];
+}
+
+"#]],
+    );
+}