'reveal_type' is not defined when using mypy_django_plugin

[blueyed]

Using reveal_type in a module fails when using plugins = project.mypy_django_plugin (via [mypy] section in setup.cfg):

% mypy project/app/admin.py
Error constructing plugin instance of NewSemanalDjangoPlugin

Traceback (most recent call last):
  File "…/project/.venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "…/project/.venv/lib/python3.9/site-packages/mypy/__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "mypy/main.py", line 90, in main
  File "mypy/build.py", line 179, in build
  File "mypy/build.py", line 228, in _build
  File "mypy/build.py", line 472, in load_plugins
  File "mypy/build.py", line 450, in load_plugins_from_config
  File "…/project/.venv/lib/python3.9/site-packages/mypy_django_plugin/main.py", line 104, in __init__
    self.django_context = DjangoContext(django_settings_module)
  File "…/project/.venv/lib/python3.9/site-packages/mypy_django_plugin/django/context.py", line 88, in __init__
    apps, settings = initialize_django(self.django_settings_module)
  File "…/project/.venv/lib/python3.9/site-packages/mypy_django_plugin/django/context.py", line 72, in initialize_django
    apps.populate(settings.INSTALLED_APPS)
  File "…/project/.venv/lib/python3.9/site-packages/django/apps/registry.py", line 122, in populate
    app_config.ready()
  File "…/project/.venv/lib/python3.9/site-packages/django/contrib/admin/apps.py", line 24, in ready
    self.module.autodiscover()
  File "…/project/.venv/lib/python3.9/site-packages/django/contrib/admin/__init__.py", line 24, in autodiscover
    autodiscover_modules('admin', register_to=site)
  File "…/project/.venv/lib/python3.9/site-packages/django/utils/module_loading.py", line 47, in autodiscover_modules
    import_module('%s.%s' % (app_config.name, module_to_search))
  File "/usr/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "…/project/app/operations/admin.py", line 928, in <module>
    reveal_type(FooAdmin)
NameError: name 'reveal_type' is not defined

System information

• OS:
• python version: Python 3.9.2
• django version: Django 3.1.8
• mypy version: mypy 0.812
• django-stubs version: f003968 (current master)

[sobolevn]

Yes, this happens because we first run django.setup() and reveal_type is not defined in runtime.

I suggest to use this hack:

from typing import TYPE_CHECKING

if not TYPE_CHECKING:
   reveal_type = print

[blueyed]

Yes, this happens because we first run django.setup() and reveal_type is not defined in runtime.

Thanks for the explanation and the workaround.
I think this warrants an answer/mention in the README/FAQ probably, doesn't it? (I've wondered not having found an issue for it already).

But I'd also like to clarify if there isn't something that could be done to fix/improve this in general, i.e. in case plugins are not really meant to import modules / run code already (what (the "custom") django.setup() does (

django-stubs/mypy_django_plugin/django/context.py

Lines 69 to 72 in f003968

	if not settings.configured:
	settings._setup()
	apps.populate(settings.INSTALLED_APPS)

)); maybe there is a later (mypy) plugin hook that should/could be used?

As for the hack the following appears to be more feasible (as an editor snippet/shortcut then):

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    reveal_type(expr)

And django-stubs itself could maybe add something like the following (while running "django.setup()")?

        from typing import TYPE_CHECKING

        if not TYPE_CHECKING:
            import builtins

            builtins.reveal_type = lambda _: None
            builtins.reveal_locals = lambda: None

[sobolevn]

Hm, probably we can add builtins patch into https://github.com/typeddjango/django-stubs/tree/master/django_stubs_ext 🤔

Do you want to work on this?

[blueyed]

Hm, probably we can add builtins patch into https://github.com/typeddjango/django-stubs/tree/master/django_stubs_ext thinking

Sounds good!

Do you want to work on this?

=> #591

[blueyed]

@sobolevn
After doing #591 I've thought that it might be better to only do this patching during the "django.setup()" - like initially suggested here.

I think it a) should not require to use the patch() method, and b) should not be in place during runtime in general (after the (apparently necessary/unavoidable) "setup").

[sobolevn]

Yes, looks like it is a good idea indeed. But, 0.2.0 is already released, we can rework how it is done in the 0.3.0.

[sebastian-philipp]

facing the same issue right now

[sobolevn]

You have reveal_type somewhere in your code, don't forget to use from typing import reveal_type

[sebastian-philipp]

sure about this?

$ python -m venv venv                                      
$ . ./venv/bin/activate          
$ pip install mypy > /dev/null
$ echo "x: int = 0" > file.py
$ echo "reveal_type(x)" >> file.py
$ mypy file.py 
file.py:2: note: Revealed type is "builtins.int"
$

[sobolevn]

Yes, I am sure :)

» echo "x: int = 0" > file.py                                                   
» echo "reveal_type(x)" >> file.py                                                                                                        
» python file.py
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/mypy/file.py", line 2, in <module>
    reveal_type(x)
    ^^^^^^^^^^^
NameError: name 'reveal_type' is not defined

With import:

» echo "x: int = 0" > file.py                                                                                                       
» echo "from typing_extensions import reveal_type" >> file.py                          
» echo "reveal_type(x)" >> file.py                                                                              
» python file.py
Runtime type is 'int'

[intgr]

Mypy doesn't require reveal_type import, but Python itself does require it to be imported.