adding a _typing module

this is a place that *must* only be imported inside a if
typing.TYPE_CHECKING block. It is a mixture of smoothing over thinigs
that moved from typing_extensions to typing in later python versions and
useful but typing only code.

This makes typing_extensions required for python versions older than
3.8 *when running mypy*. typing_extensions should *only* be imported
inside an `if typing.TYPE_CHECKING` block (include the new _typing.py
module) to ensure that it doesn't become a runtime dependency

1 files changed, 3 insertions, 0 deletions

diff --git a/setup.cfg b/setup.cfg
index 2ce0c4a..7c49b71 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -43,6 +43,9 @@ console_scripts =
 [options.extras_require]
 progress =
   tqdm
+typing =
+  mypy
+  typing_extensions; python_version <"3.8"
 
 [options.packages.find]
 include = mesonbuild, mesonbuild.*