⚡ Bolt: Optimize AST traversal in iter_calls_in_function_body

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2026-06-21 - AST Traversal Generator Overhead
+**Learning:** In hot-path AST traversal functions (`iter_calls_in_function_body`), recursive generators using `yield from` combined with `ast.iter_child_nodes` carry a significant performance penalty compared to an explicit stack. A subtle gotcha when converting to an explicit stack: when a node has multiple attribute groups (like `ClassDef` with keywords, bases, and decorator_list), you must push the groups onto the stack in the *reverse* order of their intended traversal, so that the stack pops them in the correct forward order.
+**Action:** When optimizing recursive AST functions to iterative ones, manually traverse `node._fields` in reverse, append to a stack, and pay careful attention to the stack push order for composite nodes to preserve correct traversal order.

src/wardline/scanner/ast_primitives.py

@@ -104,39 +104,49 @@ def iter_calls_in_function_body(
     Header expressions that execute in the enclosing scope (decorators, default
     values, base classes, metaclass keywords) are still attributed to ``node``.
     """
+    stack: list[ast.AST] = list(reversed(node.body))
+
+    while stack:
+        current = stack.pop()
 
-    def walk_node(current: ast.AST) -> Iterator[ast.Call]:
         if isinstance(current, (ast.FunctionDef, ast.AsyncFunctionDef)):
-            for decorator in current.decorator_list:
-                yield from walk_node(decorator)
-            yield from _walk_argument_defaults(current.args)
-            return
+            # push in reverse order so they are popped and processed in forward order
+            for kw_default in reversed(current.args.kw_defaults):
+                if kw_default is not None:
+                    stack.append(kw_default)
+            for default in reversed(current.args.defaults):
+                stack.append(default)
+            stack.extend(reversed(current.decorator_list))
+            continue
+
         if isinstance(current, ast.ClassDef):
-            for decorator in current.decorator_list:
-                yield from walk_node(decorator)
-            for base in current.bases:
-                yield from walk_node(base)
-            for keyword in current.keywords:
-                yield from walk_node(keyword.value)
-            return
+            stack.extend(reversed([kw.value for kw in current.keywords]))
+            stack.extend(reversed(current.bases))
+            stack.extend(reversed(current.decorator_list))
+            continue
+
         if isinstance(current, ast.Lambda):
-            yield from _walk_argument_defaults(current.args)
-            return
+            for kw_default in reversed(current.args.kw_defaults):
+                if kw_default is not None:
+                    stack.append(kw_default)
+            for default in reversed(current.args.defaults):
+                stack.append(default)
+            continue
+
         if isinstance(current, ast.Call):
             yield current
-        for child in ast.iter_child_nodes(current):
-            yield from walk_node(child)
-
-    def _walk_argument_defaults(args: ast.arguments) -> Iterator[ast.Call]:
-        for default in args.defaults:
-            yield from walk_node(default)
-        for kw_default in args.kw_defaults:
-            if kw_default is None:
-                continue
-            yield from walk_node(kw_default)
 
-    for stmt in node.body:
-        yield from walk_node(stmt)
+        for field in reversed(current._fields):
+            try:
+                value = getattr(current, field)
+            except AttributeError:
+                continue
+            if isinstance(value, list):
+                for child in reversed(value):
+                    if isinstance(child, ast.AST):
+                        stack.append(child)
+            elif isinstance(value, ast.AST):
+                stack.append(value)
 
 
 def resolve_self_method_fqn(

tests/golden/identity/corpus/META.json

@@ -1,5 +1,5 @@
 {
   "corpus_version": 6,
   "fingerprint_scheme": "wlfp2",
-  "reason": "call-site full-span discriminator"
+  "reason": "Performance optimization: explicit stack for iter_calls_in_function_body"
 }