fix(flow): stop cyclic walks after unreachable continue

Track visited flow ids once loop control can feed a walk back into an
earlier loop label. If a walk revisits a flow node, fall back to the
declared reference type instead of walking forever.

Fixes #1146
Assisted-by: Codex

Author: lewis6991

crates/emmylua_code_analysis/src/compilation/test/flow.rs

@@ -1,6 +1,6 @@
 #[cfg(test)]
 mod test {
-    use crate::{DiagnosticCode, LuaType, VirtualWorkspace};
+    use crate::{DiagnosticCode, EmmyrcLuaVersion, LuaType, VirtualWorkspace};
     use emmylua_parser::{LuaAstToken, LuaLocalName};
     use ntest::timeout;
 
@@ -1475,6 +1475,30 @@ end
         assert_eq!(ws.expr_ty("after_loop"), ws.ty("string?"));
     }
 
+    #[test]
+    #[timeout(5000)]
+    fn test_unreachable_continue_loop_after_return_does_not_cycle() {
+        let mut ws = VirtualWorkspace::new();
+        let mut emmyrc = ws.get_emmyrc();
+        emmyrc.runtime.version = EmmyrcLuaVersion::LuaJITExt;
+        ws.update_emmyrc(emmyrc);
+
+        ws.def(
+            r#"
+        local side_effect = 0
+        return boolean
+
+        local continue_counter = 0
+        for i = 1, 5 do
+            if i % 2 == 0 then
+                continue
+            end
+            continue_counter = continue_counter + 1
+        end
+        "#,
+        );
+    }
+
     #[test]
     fn test_for_in_loop_post_flow_keeps_incoming_type_after_break() {
         let mut ws = VirtualWorkspace::new_with_init_std_lib();

crates/emmylua_code_analysis/src/semantic/infer/narrow/get_type_at_flow.rs

@@ -1322,7 +1322,18 @@ impl<'a> FlowTypeEngine<'a> {
     // produces a final type, needs another query first, or reaches a saved
     // continuation point like a branch merge.
     fn evaluate_walk(&mut self, mut walk: QueryWalk) -> Result<SchedulerStep, InferFailReason> {
+        // Most walks are acyclic, so only start tracking after loop control can
+        // feed a later flow node back into an earlier loop label.
+        let mut visited_flow_ids = None::<HashSet<FlowId>>;
+
         loop {
+            if let Some(visited_flow_ids) = &mut visited_flow_ids
+                && !visited_flow_ids.insert(walk.antecedent_flow_id)
+            {
+                let result_type = get_var_ref_type(self.db, self.cache, &walk.query.var_ref_id)?;
+                return Ok(self.finish_walk(walk, result_type));
+            }
+
             // Replays can suspend a query and later revisit an older antecedent
             // that another query already finished. Use that cached type instead
             // of walking back through the same replay chain again.
@@ -1356,6 +1367,15 @@ impl<'a> FlowTypeEngine<'a> {
                 | FlowNodeKind::Continue
                 | FlowNodeKind::Return
                 | FlowNodeKind::ForIStat(_) => {
+                    if matches!(
+                        &flow_node.kind,
+                        FlowNodeKind::LoopLabel | FlowNodeKind::Continue
+                    ) && visited_flow_ids.is_none()
+                    {
+                        let mut visited = HashSet::new();
+                        visited.insert(walk.antecedent_flow_id);
+                        visited_flow_ids = Some(visited);
+                    }
                     walk.antecedent_flow_id = get_single_antecedent(flow_node)?;
                 }
                 FlowNodeKind::BranchLabel | FlowNodeKind::NamedLabel(_) => {