Fix another bug when reaching macro expansion limit caused a stack overflow

This time without missing bindings.

Solve it by returning to the old ways, i.e. just throw the extra nodes away.

In other words, I acknowledge defeat.

Author: ChayimFriedman2

src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/macro_error.rs

@@ -291,4 +291,30 @@ mod prim_never {}
 "#,
         );
     }
+
+    #[test]
+    fn no_stack_overflow_for_missing_binding() {
+        check_diagnostics(
+            r#"
+#[macro_export]
+macro_rules! boom {
+    (
+        $($code:literal),+,
+        $(param: $param:expr,)?
+    ) => {{
+        let _ = $crate::boom!(@param $($param)*);
+    }};
+    (@param) => { () };
+    (@param $param:expr) => { $param };
+}
+
+fn it_works() {
+    // NOTE: there is an error, but RA crashes before showing it
+    boom!("RAND", param: c7.clone());
+               // ^^^^^ error: expected literal
+}
+
+        "#,
+        );
+    }
 }

src/tools/rust-analyzer/crates/mbe/src/expander/transcriber.rs

@@ -448,6 +448,7 @@ fn expand_repeat(
     let mut counter = 0;
     let mut err = None;
 
+    let initial_restore_point = builder.restore_point();
     let mut restore_point = builder.restore_point();
     loop {
         let ExpandResult { value: (), err: e } =
@@ -465,6 +466,10 @@ fn expand_repeat(
 
         counter += 1;
         if counter == limit {
+            // FIXME: This is a bug here, we get here when we shouldn't, see https://github.com/rust-lang/rust-analyzer/issues/18910.
+            // If we don't restore we emit a lot of nodes which causes a stack overflow down the road. For now just ignore them,
+            // there is always an error here anyway.
+            builder.restore(initial_restore_point);
             err = Some(ExpandError::new(ctx.call_site, ExpandErrorKind::LimitExceeded));
             break;
         }