fail loudly when the app package has no __init__.py (#7304)

* fail loudly when the app package has no __init__.py

* Create missing app package markers before backend import

* Test package marker creation and existing-file safety

* Update bugfix note for automatic package markers

* Guard package marker creation for namespace and read-only apps

* Preserve nested regular package imports

* Use module target for Granian backend imports

* Preserve app module validation for Granian target

* Restore sys.path after missing-module test

---------

Co-authored-by: Farhan Ali Raza <62690310+FarhanAliRaza@users.noreply.github.com>
Co-authored-by: Masen Furer <m_github@0x26.net>

Author: 3 people

news/7258.bugfix.md

@@ -0,0 +1 @@
+Load backend apps by their configured module name so state updates work even when the app package has no `__init__.py`.

reflex/utils/exec.py

@@ -553,7 +553,8 @@ def get_app_instance_from_file() -> str:
     Returns:
         The app module for the backend.
     """
-    return f"{get_app_file()}:{constants.CompileVars.APP}"
+    get_app_file()
+    return get_app_instance()
 
 
 def run_backend(

tests/units/utils/test_granian_module_target.py

@@ -0,0 +1,76 @@
+"""Regression for a backend app whose package has no __init__.py."""
+
+import importlib
+import sys
+from pathlib import Path
+
+import pytest
+
+from reflex.utils import exec as exec_utils
+
+
+@pytest.mark.parametrize("installed", [False, True])
+def test_granian_target_keeps_configured_module_without_writing_marker(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, installed: bool
+):
+    from granian._internal import prepare_import
+
+    root = tmp_path / "installed" if installed else tmp_path
+    module = "installed_app_7304" if installed else "myapp.myapp"
+    module_file = root.joinpath(*module.split(".")).with_suffix(".py")
+    module_file.parent.mkdir(parents=True)
+    module_file.write_text("app = object()\n")
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.syspath_prepend(str(root))
+    original_path = sys.path.copy()
+    if installed:
+        from reflex_base.config import Config
+
+        config = Config(app_name="myapp", app_module_import=module)
+        monkeypatch.setattr(exec_utils, "get_config", lambda: config)
+    else:
+        monkeypatch.setattr(exec_utils, "get_app_module", lambda: module)
+
+    target, _ = exec_utils.get_app_instance_from_file().split(":", 1)
+    assert prepare_import(target) == module
+    sys.modules.pop(module, None)
+    try:
+        assert importlib.import_module(target).app is not None
+        assert not (module_file.parent / "__init__.py").exists()
+    finally:
+        sys.modules.pop(module, None)
+        for index in range(1, len(module.split("."))):
+            sys.modules.pop(".".join(module.split(".")[:index]), None)
+        sys.path[:] = original_path
+
+
+def test_granian_target_rejects_missing_module(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    """The module target still provides the existing missing-module error."""
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.syspath_prepend(str(tmp_path))
+    monkeypatch.setattr(exec_utils, "get_app_module", lambda: "missing.app")
+    with pytest.raises(ImportError, match=r"Module missing\.app not found"):
+        exec_utils.get_app_instance_from_file()
+
+
+def test_granian_target_adds_project_root_to_sys_path(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    """An installed console script may not put the project root on sys.path."""
+    app_dir = tmp_path / "local_app_7304"
+    app_dir.mkdir()
+    (app_dir / "app.py").write_text("app = object()\n")
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setattr(
+        sys, "path", [entry for entry in sys.path if entry != str(tmp_path)]
+    )
+    monkeypatch.setattr(exec_utils, "get_app_module", lambda: "local_app_7304.app")
+
+    target, _ = exec_utils.get_app_instance_from_file().split(":", 1)
+    try:
+        assert importlib.import_module(target).app is not None
+    finally:
+        sys.modules.pop(target, None)
+        sys.modules.pop("local_app_7304", None)