Reload syntax error robustness

src/functions_framework/__init__.py

@@ -357,11 +357,30 @@ def handle_none(rv):
 
     # Execute the module, within the application context
     with _app.app_context():
-        spec.loader.exec_module(source_module)
+        try:
+            spec.loader.exec_module(source_module)
+            function = _function_registry.get_user_function(
+                source, source_module, target
+            )
+        except Exception as e:
+            if werkzeug.serving.is_running_from_reloader():
+                # When reloading, print out the error immediately, but raise
+                # it later so the debugger or server can handle it.
+                import traceback
+
+                traceback.print_exc()
+                err = e
+
+                def function(*_args, **_kwargs):
+                    raise err from None
+
+            else:
+                # When not reloading, raise the error immediately so the
+                # command fails.
+                raise e from None
 
     # Get the configured function signature type
     signature_type = _function_registry.get_func_signature_type(target, signature_type)
-    function = _function_registry.get_user_function(source, source_module, target)
 
     _configure_app(_app, function, signature_type)
 

tests/test_functions.py

@@ -323,6 +323,19 @@ def test_invalid_function_definition_function_syntax_error():
     )
 
 
+def test_invalid_function_definition_function_syntax_robustness_with_debug(monkeypatch):
+    monkeypatch.setattr(
+        functions_framework.werkzeug.serving, "is_running_from_reloader", lambda: True
+    )
+    source = TEST_FUNCTIONS_DIR / "background_load_error" / "main.py"
+    target = "function"
+
+    client = create_app(target, source).test_client()
+
+    resp = client.get("/")
+    assert resp.status_code == 500
+
+
 def test_invalid_function_definition_missing_dependency():
     source = TEST_FUNCTIONS_DIR / "background_missing_dependency" / "main.py"
     target = "function"