add automated semicolon insertion test

crates/hir_def/src/macro_expansion_tests/mbe.rs

@@ -299,6 +299,34 @@ fn baz() {
     )
 }
 
+#[test]
+fn asi() {
+    // Thanks, Christopher!
+    //
+    // https://internals.rust-lang.org/t/understanding-decisions-behind-semicolons/15181/29
+    check(
+        r#"
+macro_rules! asi { ($($stmt:stmt)*) => ($($stmt)*); }
+
+fn main() {
+    asi! {
+        let a = 2
+        let b = 5
+        drop(b-a)
+        println!("{}", a+b)
+    }
+}
+"#,
+        expect![[r#"
+macro_rules! asi { ($($stmt:stmt)*) => ($($stmt)*); }
+
+fn main() {
+    let a = 2let b = 5drop(b-a)println!("{}", a+b)
+}
+"#]],
+    )
+}
+
 #[test]
 fn test_match_group_empty_fixed_token() {
     check(