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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 19:33:14 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 19:33:14 +0000 |
commit | 36d22d82aa202bb199967e9512281e9a53db42c9 (patch) | |
tree | 105e8c98ddea1c1e4784a60a5a6410fa416be2de /third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py | |
parent | Initial commit. (diff) | |
download | firefox-esr-36d22d82aa202bb199967e9512281e9a53db42c9.tar.xz firefox-esr-36d22d82aa202bb199967e9512281e9a53db42c9.zip |
Adding upstream version 115.7.0esr.upstream/115.7.0esr
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py')
-rw-r--r-- | third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py b/third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py new file mode 100644 index 0000000000..77a8b9185a --- /dev/null +++ b/third_party/python/setuptools/pkg_resources/_vendor/packaging/_typing.py @@ -0,0 +1,48 @@ +"""For neatly implementing static typing in packaging. + +`mypy` - the static type analysis tool we use - uses the `typing` module, which +provides core functionality fundamental to mypy's functioning. + +Generally, `typing` would be imported at runtime and used in that fashion - +it acts as a no-op at runtime and does not have any run-time overhead by +design. + +As it turns out, `typing` is not vendorable - it uses separate sources for +Python 2/Python 3. Thus, this codebase can not expect it to be present. +To work around this, mypy allows the typing import to be behind a False-y +optional to prevent it from running at runtime and type-comments can be used +to remove the need for the types to be accessible directly during runtime. + +This module provides the False-y guard in a nicely named fashion so that a +curious maintainer can reach here to read this. + +In packaging, all static-typing related imports should be guarded as follows: + + from packaging._typing import TYPE_CHECKING + + if TYPE_CHECKING: + from typing import ... + +Ref: https://github.com/python/mypy/issues/3216 +""" + +__all__ = ["TYPE_CHECKING", "cast"] + +# The TYPE_CHECKING constant defined by the typing module is False at runtime +# but True while type checking. +if False: # pragma: no cover + from typing import TYPE_CHECKING +else: + TYPE_CHECKING = False + +# typing's cast syntax requires calling typing.cast at runtime, but we don't +# want to import typing at runtime. Here, we inform the type checkers that +# we're importing `typing.cast` as `cast` and re-implement typing.cast's +# runtime behavior in a block that is ignored by type checkers. +if TYPE_CHECKING: # pragma: no cover + # not executed at runtime + from typing import cast +else: + # executed at runtime + def cast(type_, value): # noqa + return value |