FlaskGroup does not work when nested in a click.group

[gustapia06]

Expected Behavior

When using Flask CLI, I came to the case that we have a group of commands for a big program that uses click.

# main group
@click.group()
@click.pass_context
def my_big_cli_group(ctx):
    pass

# sub group
@my_big_cli_group.group()
@click.pass_context
def my_nested_group(ctx):
    pass

# command for sub group
@my_nested_group.command()
@click.pass_context
@click.option('-s', '--start', is_flag=True)
def my_command(ctx, start):
    click.echo(start)

The issue comes when nesting my flask app into the bigger group using cls=FlaskGroup and passing my create_app factory function.

# flask app sub group
@my_big_cli_group.group(cls=FlaskGroup, create_app=create_app)
@click.pass_context
def my_flask_app(ctx):
    pass

After running my setup.py pointing my entry point to 'my_big_cli = path.to:my_big_cli_group', I should expect the app to start once I do:

$ my_big_cli my_flask_app run

Actual Behavior

Instead, I get a flask.cli.NoAppException. It seems that create_app does not get passed on to Group.group instances on click.

Traceback (most recent call last):
 File “/Users/the_user/Desktop/venv/lib/python3.7/site-packages/flask/cli.py”, line 540, in list_commands
   rv.update(info.load_app().cli.list_commands(ctx))
 File “/Users/the_user/Desktop/venv/lib/python3.7/site-packages/flask/cli.py”, line 393, in load_app
   ‘Could not locate a Flask application. You did not provide ’
flask.cli.NoAppException: Could not locate a Flask application. You did not provide the “FLASK_APP” environment variable, and a “wsgi.py” or “app.py” module was not found in the current directory.

Work around

If I don't nest the flask app into a group but rather make it a new click.group, then after changing my setup.py to point to this new entry point as well, everything works as expected.

# flask app group
@click.group(cls=FlaskGroup, create_app=create_app)
@click.pass_context
def my_flask_app(ctx):
    pass

Then

$ my_flask_app run

works perfectly fine

Environment

• Python version: 3.7.3
• Flask version: 1.0.3
• Werkzeug version: 0.15.4

[frostming]

There are some bootstrap code in FlaskGroup.main(), so I think it is not allowed to nest it in another group, because the function is never called.

[gustapia06]

Ah, interesting. Could there be any workaround for this to be allowed? I guess at the end Flask should be fully compatible with all click functionalities (group nesting being one of the main ones).

[frostming]

Passing create_app as a parameter doesn't work in this case, but you can still use FLASK_APP environment variable to do the trick. Note that some functionalities are still missing, such as dotenv loading.

[u8sand]

I also came across this issue, I dug into the source and was able to make a minor change which seems to do the trick. I have yet to test it more thoroughly however, perhaps someone here can figure out if this affects something else.

Quite simply I re-write FlaskGroup and replace main with make_context (naturally, the call and the super()) here https://github.com/pallets/flask/blob/master/src/flask/cli.py#L578-L597

This is because in click, one of the first things that are done in main is to call make_context with kwargs (https://github.com/pallets/click/blob/master/src/click/core.py#L809)

Which ends up here: https://github.com/pallets/click/blob/35f73b8c2c314e56968de8bc483da9a84ac5c53e/src/click/core.py#L712
It looks to me like injecting kwargs into this function instead of main should work just as well. In my simple tests, this seems to enable me to run the flask apps using the new FlaskGroup in sub groups.

After additional testing I may consider writing a PR if no one beats me to it.

[chatne]

@u8sand Thanks a lot for your research!

For anyone else wondering how to avoid this issue, this is the code I used (simplified a bit):

class CustomGroup(FlaskGroup):
    def make_context(self, *args, **extra):
        obj = extra.get("obj")
        if obj is None:
            obj = ScriptInfo(create_app=self.create_app, set_debug_flag=self.set_debug_flag)
        extra["obj"] = obj

        return super().make_context(*args, **extra)

@click.group(cls=CustomGroup)
...