Export types of builtin fixtures for type annotations #8017

bluetech · 2020-11-09T17:00:48Z

The first commit is a hack to fix the issue discussed here: #7469 (comment)

The second commit is a partial fix for #7469 -- only for the fixture types. If this is accepted I will work on the other items on the list, but the fixtures are the most urgent so I'm starting with them.

Please see the commit messages for the approach I took, particularly the "privacy" mechanism in the second commit.

src/_pytest/pytester.py

nicoddemus · 2020-11-10T18:29:07Z

Unfortunately the _ispytest solution is very verbose requiring many changes, but I don't have a better suggestion. 👍

src/_pytest/config/__init__.py

src/_pytest/pytester_assertions.py

src/_pytest/cacheprovider.py

src/_pytest/deprecated.py

changelog/7469.improvement.rst

graingert

I think you're missing several *, _ispytest: bool = False defaults

…itself An upcoming commit wants to import from `_pytest.pytester` in the public `pytest` module. This means that `_pytest.pytester` would start to get imported during import time, which it hasn't up to now -- it was imported by the plugin loader (if requested). When a plugin is loaded, it is subjected to assertion rewriting, but only if the module isn't imported yet, it issues a warning "Module already imported so cannot be rewritten" and skips the rewriting. So we'd end up with the pytester plugin not being rewritten, but it wants to be. Absent better ideas, the solution here is to split the pytester assertions to their own plugin (which will always only be imported by the plugin loader) and exclude pytester itself from plugin rewriting.

In order to allow users to type annotate fixtures they request, the types need to be imported from the `pytest` namespace. They are/were always available to import from the `_pytest` namespace, but that is not guaranteed to be stable. These types are only exported for the purpose of typing. Specifically, the following are *not* public: - Construction (`__init__`) - Subclassing - staticmethods and classmethods We try to combat them being used anyway by: - Marking the classes as `@final` when possible (already done). - Not documenting private stuff in the API Reference. - Using `_`-prefixed names or marking as `:meta private:` for private stuff. - Adding a keyword-only `_ispytest=False` to private constructors, warning if False, and changing pytest itself to pass True. In the future it will (hopefully) become a hard error. Hopefully that will be enough.

bluetech · 2020-11-13T09:28:31Z

I think you're missing several *, _ispytest: bool = False defaults

Whoops!

Thanks for the review. I updated the PR, you can see the changes here.

bluetech · 2020-12-05T19:51:10Z

Merging per @nicoddemus's approval and replies to @graingert's comments. Let's see how the _is_pytest stuff works out!

bluetech changed the title ~~Export types of builtin fixture for type annotations~~ Export types of builtin fixtures for type annotations Nov 9, 2020

nicoddemus approved these changes Nov 10, 2020

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