move caching to a new function that wraps AST parsing

Author: ngoldbaum

src/pytest_run_parallel/plugin.py

@@ -172,7 +172,7 @@ def pytest_itemcollected(item):
     skipped_functions = [
         x.split(".") for x in item.config.getini("thread_unsafe_functions")
     ]
-    skipped_functions = frozenset((".".join(x[:-1]), x[-1]) for x in skipped_functions)
+    skipped_functions = {(".".join(x[:-1]), x[-1]) for x in skipped_functions}
 
     if n_workers > 1:
         thread_unsafe, thread_unsafe_reason = identify_thread_unsafe_nodes(

src/pytest_run_parallel/utils.py

@@ -118,12 +118,16 @@ def visit_Assign(self, node):
 
 
 @functools.lru_cache
+def ast_parse(fn):
+    src = inspect.getsource(fn)
+    return ast.parse(dedent(src))
+
+
 def identify_thread_unsafe_nodes(fn, skip_set, level=0):
     if is_hypothesis_test(fn):
         return True, "uses hypothesis"
     try:
-        src = inspect.getsource(fn)
-        tree = ast.parse(dedent(src))
+        tree = ast_parse(fn)
     except Exception:
         return False, None
     visitor = ThreadUnsafeNodeVisitor(fn, skip_set, level=level)