Generate module version file at build

Gunicore rely on `eventlet.__version__` [1], however
this data have been removed during our modernization
of the continuous deployment mechanisms [2].

People reported problem with gunicore after 0.34.1 [3][4],
so, it could be worth to reintroduce similar version info,
to avoid side effects.

This patch propose to use a `hatch-vcs` hook [5] to generate
dynamically, at build, the missing data. Other solutions exists
but each of them have their own problems [6].

Indeed, considering "footgun" described in [6] I choose the
hatch-vcs approach, because, retrieving a wrong version number
during development when the lib is installed in editable mode,
is not, I think, something horrible. I prefer this side effect
rather than relying on another additional underlying library
just to print a version number when eventlet is installed in
editable mode. A new additional requirement which would be
installed anytime at runtime and production.

Moreover, sometimes you want to import a package from a
development repository tarball you just downloaded (where
there's no metadata or Git tags present). So, Using
`setuptools_scm` or `importlib.metadata.version` won't
works in that context.

Fix benoitc/gunicorn#3120

Also, update the supported python to 3.7 in a remaining
condition. Python 3.5 is not supported anymore.

[1] benoitc/gunicorn#3120
[2] #845
[3] #845 (comment)
[4] #842 (comment)
[5] https://github.com/ofek/hatch-vcs#build-hook
[6] https://github.com/maresb/hatch-vcs-footgun-example

eventlet/__init__.py

@@ -2,12 +2,12 @@
 import sys
 import warnings
 
-if sys.version_info < (3, 5):
+if sys.version_info < (3, 7):
     warnings.warn(
-        "Support for your Python version is deprecated and will be removed in the future",
+        """Your Python version is no longer supported by eventlet
+        Please consider upgrading to minimal supported Python version""",
         DeprecationWarning,
     )
-
 from eventlet import convenience
 from eventlet import event
 from eventlet import greenpool
@@ -17,7 +17,19 @@
 from eventlet import semaphore
 from eventlet import support
 from eventlet import timeout
+# NOTE(hberaud): Versions are now managed by hatch and control version.
+# hatch has a build hook which generates the version file, however,
+# if the project is installed in editable mode then the _version.py file
+# will not be updated unless the package is reinstalled (or locally rebuilt).
+# For further details, please read:
+# https://github.com/ofek/hatch-vcs#build-hook
+# https://github.com/maresb/hatch-vcs-footgun-example
+try:
+    from eventlet._version import __version__
+except ImportError:
+    __version__ = "0.0.0"
 import greenlet
+
 # Force monotonic library search as early as possible.
 # Helpful when CPython < 3.5 on Linux blocked in `os.waitpid(-1)` before first use of hub.
 # Example: gunicorn

pyproject.toml

@@ -59,3 +59,6 @@ exclude = ["tests*", "benchmarks", "examples"]
 
 [tool.hatch]
 version.source = "vcs"
+
+[tool.hatch.build.hooks.vcs]
+version-file = "eventlet/_version.py"