fix: clean up stale asset symlinks to prevent hot reload crash loop (#6163)

* fix: clean up stale asset symlinks to prevent hot reload crash loop (#6159)

When a Python module directory using rx.asset(shared=True) is renamed,
stale symlinks in assets/external/ cause Granian to enter an infinite
reload loop. Clean up broken symlinks and empty directories in
assets/external/ in App.__call__ before compilation, so the cleanup
runs on every hot reload, not just initial startup.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* address PR review: guard rmdir against dir symlinks, fix fragile test

- Add `not dirpath.is_symlink()` check before `rmdir()` to avoid
  NotADirectoryError on symlinks pointing to directories.
- Use tmp_path/monkeypatch in no-external-dir test to avoid depending
  on prior test environment state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* cr feedback: do not mutate dir while iterating over it

* do not use cwd for tests

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: masenf

reflex/app.py

@@ -615,8 +615,13 @@ def __call__(self) -> ASGIApp:
         Returns:
             The backend api.
         """
+        from reflex.assets import remove_stale_external_asset_symlinks
         from reflex.vars.base import GLOBAL_CACHE
 
+        # Clean up stale symlinks in assets/external/ before compiling, so that
+        # rx.asset(shared=True) symlink re-creation doesn't trigger further reloads.
+        remove_stale_external_asset_symlinks()
+
         self._compile(prerender_routes=should_prerender_routes())
 
         config = get_config()

reflex/assets.py

@@ -7,6 +7,35 @@
 from reflex.environment import EnvironmentVariables
 
 
+def remove_stale_external_asset_symlinks():
+    """Remove broken symlinks and empty directories in assets/external/.
+
+    When a Python module directory that uses rx.asset(shared=True) is renamed
+    or deleted, stale symlinks remain in assets/external/ pointing to the old
+    path. This cleanup prevents issues with file watchers detecting symlink
+    re-creation during import.
+    """
+    external_dir = (
+        Path.cwd() / constants.Dirs.APP_ASSETS / constants.Dirs.EXTERNAL_APP_ASSETS
+    )
+    if not external_dir.exists():
+        return
+
+    # Remove broken symlinks.
+    broken = [
+        p
+        for p in external_dir.rglob("*")
+        if p.is_symlink() and not p.resolve().exists()
+    ]
+    for path in broken:
+        path.unlink()
+
+    # Remove empty directories left behind (deepest first).
+    for dirpath in sorted(external_dir.rglob("*"), reverse=True):
+        if dirpath.is_dir() and not dirpath.is_symlink() and not any(dirpath.iterdir()):
+            dirpath.rmdir()
+
+
 def asset(
     path: str,
     shared: bool = False,

tests/units/assets/test_assets.py

@@ -6,15 +6,40 @@
 
 import reflex as rx
 import reflex.constants as constants
+from reflex.assets import remove_stale_external_asset_symlinks
 
 
-def test_shared_asset() -> None:
+@pytest.fixture
+def mock_asset_path(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
+    """Create a mock asset file and patch the current working directory.
+
+    Args:
+        tmp_path: A temporary directory provided by pytest.
+        monkeypatch: A pytest fixture for patching.
+
+    Returns:
+        The path to a tmp cwd that will be used for assets.
+    """
+    # Create a temporary directory to act as the current working directory.
+    mock_cwd = tmp_path / "mock_asset_path"
+    mock_cwd.mkdir()
+    monkeypatch.chdir(mock_cwd)
+
+    return mock_cwd
+
+
+def test_shared_asset(mock_asset_path: Path) -> None:
     """Test shared assets."""
     # The asset function copies a file to the app's external assets directory.
     asset = rx.asset(path="custom_script.js", shared=True, subfolder="subfolder")
     assert asset == "/external/test_assets/subfolder/custom_script.js"
     result_file = Path(
-        Path.cwd(), "assets/external/test_assets/subfolder/custom_script.js"
+        mock_asset_path,
+        "assets",
+        "external",
+        "test_assets",
+        "subfolder",
+        "custom_script.js",
     )
     assert result_file.exists()
 
@@ -24,17 +49,19 @@ def test_shared_asset() -> None:
     # Test the asset function without a subfolder.
     asset = rx.asset(path="custom_script.js", shared=True)
     assert asset == "/external/test_assets/custom_script.js"
-    result_file = Path(Path.cwd(), "assets/external/test_assets/custom_script.js")
+    result_file = Path(
+        mock_asset_path, "assets", "external", "test_assets", "custom_script.js"
+    )
     assert result_file.exists()
 
     # clean up
-    shutil.rmtree(Path.cwd() / "assets/external")
+    shutil.rmtree(Path(mock_asset_path) / "assets" / "external")
 
     with pytest.raises(FileNotFoundError):
         asset = rx.asset("non_existent_file.js")
 
     # Nothing is done to assets when file does not exist.
-    assert not Path(Path.cwd() / "assets/external").exists()
+    assert not Path(mock_asset_path / "assets" / "external").exists()
 
 
 @pytest.mark.parametrize(
@@ -56,13 +83,13 @@ def test_invalid_assets(path: str, shared: bool) -> None:
 
 
 @pytest.fixture
-def custom_script_in_asset_dir() -> Generator[Path, None, None]:
+def custom_script_in_asset_dir(mock_asset_path: Path) -> Generator[Path, None, None]:
     """Create a custom_script.js file in the app's assets directory.
 
     Yields:
         The path to the custom_script.js file.
     """
-    asset_dir = Path.cwd() / constants.Dirs.APP_ASSETS
+    asset_dir = mock_asset_path / constants.Dirs.APP_ASSETS
     asset_dir.mkdir(exist_ok=True)
     path = asset_dir / "custom_script.js"
     path.touch()
@@ -79,3 +106,49 @@ def test_local_asset(custom_script_in_asset_dir: Path) -> None:
     """
     asset = rx.asset("custom_script.js", shared=False)
     assert asset == "/custom_script.js"
+
+
+def test_remove_stale_external_asset_symlinks(mock_asset_path: Path) -> None:
+    """Test that stale symlinks and empty dirs in assets/external/ are cleaned up."""
+    external_dir = (
+        mock_asset_path / constants.Dirs.APP_ASSETS / constants.Dirs.EXTERNAL_APP_ASSETS
+    )
+
+    # Set up: create a subdirectory with a broken symlink.
+    stale_dir = external_dir / "old_module" / "subpkg"
+    stale_dir.mkdir(parents=True, exist_ok=True)
+    stale_symlink = stale_dir / "missing_file.js"
+    stale_symlink.symlink_to("/nonexistent/path/missing_file.js")
+    assert stale_symlink.is_symlink()
+    assert not stale_symlink.resolve().exists()
+
+    # Also create a valid symlink that should be preserved.
+    valid_dir = external_dir / "valid_module"
+    valid_dir.mkdir(parents=True, exist_ok=True)
+    valid_target = Path(__file__).parent / "custom_script.js"
+    valid_symlink = valid_dir / "custom_script.js"
+    valid_symlink.symlink_to(valid_target)
+    assert valid_symlink.is_symlink()
+    assert valid_symlink.resolve().exists()
+
+    remove_stale_external_asset_symlinks()
+
+    # Broken symlink and its empty parent dirs should be removed.
+    assert not stale_symlink.exists()
+    assert not stale_symlink.is_symlink()
+    assert not stale_dir.exists()
+    assert not (external_dir / "old_module").exists()
+
+    # Valid symlink should be preserved.
+    assert valid_symlink.is_symlink()
+    assert valid_symlink.resolve().exists()
+
+
+def test_remove_stale_symlinks_no_external_dir(mock_asset_path: Path) -> None:
+    """Test that cleanup is a no-op when assets/external/ doesn't exist."""
+    external_dir = (
+        mock_asset_path / constants.Dirs.APP_ASSETS / constants.Dirs.EXTERNAL_APP_ASSETS
+    )
+    assert not external_dir.exists()
+    # Should not raise.
+    remove_stale_external_asset_symlinks()