util: add project_wheel_metadata

[FFY00]

Signed-off-by: Filipe Laíns lains@riseup.net

[layday]

This is gonna break --strict downstream. Just add __all__ in build.util.

[FFY00]

This is for SimplePath, which is not explicitly re-exported in importlib.

[gaborbernat]

If so you want to set that option for only that lib, not globally. Or add a type ignore at the location of the import.

[layday]

We shouldn't need to import SimplePath after python/importlib_metadata#335 is merged.

[henryiii]

I think we should move to pyproject.toml mypy config, it's much cleaner and makes per-lib settings prettier if we need them. Not in this PR, though.

[FFY00]

Sure, feel free to open a PR.

[layday]

Does it return PackageMetadata if you don't have importlib-metadata >= 4.1.0?

[gaborbernat]

Also on python3.8 or later this packagemetadata import would fail not?

[FFY00]

Older versions are not typed, but they do return an object that implements the protocol, tox -e py36-min works fine, and it pins importlib-metadata==0.22. I can bump the version though, if you think it would be better.

[henryiii]

I generally assume that static typing only supports a narrow set of versions (usually exactly pinned versions to the latest dependencies). I wouldn't worry about bumping a runtime version for typing, or about whether older versions fail typing checks. So I'm happy with it as is.

[layday]

but they do return an object that implements the protocol

The protocol declares json, which does not exist on email.Message, and only a small subset of email.Message's methods.

[FFY00]

Hum, right. We need to keep the type hints and the implementation in sync then. I think the best option is for us to declare the fixed SimplePath protocol and cast it, or simply have a # type: ignore instead of pulling importlib_metadata for Python >= 3.8 only when type checking.

[layday]

Or just return the distribution and let consumers call .metadata.

[FFY00]

The distribution is dependent on the metadata path being on the system. We would have to make this a context manager to do the cleanup of the temporary directory, which is just more boilerplate for people to write.

[FFY00]

Nevermind, we would need to cast to the incorrect SimplePath, which will break in the future. I just went with a # type: ignore.

[layday]

There's a new version of importlib-metadata out if you have time to revisit this PR @FFY00.

[layday]

and not typing.TYPE_CHECKING?

[FFY00]

To make it use the fixed SimplePath protocol in importlib-metadata.

[layday]

I don't like that we're mixing runtime with type checking checks. Was the broken protocol shipped as part of the stdlib? Otherwise this shouldn't be necessary.

[FFY00]

Yes, https://github.com/python/cpython/blob/8868d48712aee2b490efaf60bed8dfe9fb14d6b7/Lib/importlib/metadata/_meta.py#L32.

Do you have any alternative? We know the code in importlib.metadata is compatible, it's just the protocol is wrong. I don't see another way of making mypy happy without adding a dependency on importlib_metadata for Python < 3.11, without it being actually needed at runtime, or sprinkling some # type: ignore comments.

[layday]

Let's just pull TYPE_CHECKING out of the version check:

diff --git a/src/build/util.py b/src/build/util.py
index cd2b95a..f56901a 100644
--- a/src/build/util.py
+++ b/src/build/util.py
@@ -13,18 +13,15 @@
 import build
 import build.env

-
-if sys.version_info >= (3, 8) and not typing.TYPE_CHECKING:
+if typing.TYPE_CHECKING:
+    import importlib_metadata
+elif sys.version_info >= (3, 8):
     import importlib.metadata as importlib_metadata
 else:
     import importlib_metadata


-if typing.TYPE_CHECKING:
-    from importlib_metadata import PackageMetadata
-
-
-def _project_wheel_metadata(builder: build.ProjectBuilder) -> 'PackageMetadata':
+def _project_wheel_metadata(builder: build.ProjectBuilder) -> 'importlib_metadata.PackageMetadata':
     with tempfile.TemporaryDirectory() as tmpdir:
         path = pathlib.Path(builder.metadata_path(tmpdir))
         # https://github.com/python/importlib_metadata/pull/343
@@ -34,7 +31,7 @@ def _project_wheel_metadata(builder: build.ProjectBuilder) -> 'PackageMetadata':
 def project_wheel_metadata(
     srcdir: Union[str, 'os.PathLike[str]'],
     isolated: bool = True,
-) -> 'PackageMetadata':
+) -> 'importlib_metadata.PackageMetadata':
     """
     Return the wheel metadata for a project.

[FFY00]

This protocol is still not fixed in importlib_metadata (needs python/importlib_metadata#342, see python/importlib_metadata#343), so I think we should just go ahead with the # type: ignore as we know the code is definitely correct.

[henryiii]

You should get a message about an unnecessary type ignore when this does get fixed, so don't see any harm.

[gaborbernat]

Add an __all__ with this in it to mark this method as public 👍 (and hides importlib_metadata)

[henryiii]

I also usually recommend:

def __dir__() -> Tuple[Any, ...]:
    return __all__

This fixes tab completion the REPL or IPython in Python 3.7+ to only show public methods.

[FFY00]

I am gonna do __all__ to keep in sync with the other modules, and then you can open a PR moving to that form.

[FFY00]

Does anyone have other comments?

[layday]

LGTM!