strip trailing + from version number of local Python builds

crates/uv-interpreter/src/get_interpreter_info.py

@@ -19,6 +19,43 @@ def format_full_version(info):
 else:
     implementation_version = "0"
     implementation_name = ""
+
+python_full_version = platform.python_version()
+# For local builds of Python, at time of writing, the version numbers end with
+# a `+`. This makes the version non-PEP-440 compatible since a `+` indicates
+# the start of a local segment which must be non-empty. Thus, `uv` chokes on it
+# and spits out an error[1] when trying to create a venv using a "local" build
+# of Python. Arguably, the right fix for this is for CPython to use a PEP-440
+# compatible version number[2].
+#
+# However, as a work-around for now, as suggested by pradyunsg[3] as one
+# possible direction forward, we strip the `+`.
+#
+# This fix does unfortunately mean that one cannot specify a Python version
+# constraint that specifically selects a local version[4]. But at the time of
+# writing, it seems reasonable to block such functionality on this being fixed
+# upstream (in some way).
+#
+# Another alternative would be to treat such invalid versions as strings (which
+# is what PEP-508 suggests), but this leads to undesirable behavior in this
+# case. For example, let's say you have a Python constraint of `>=3.9.1` and
+# a local build of Python with a version `3.11.1+`. Using string comparisons
+# would mean the constraint wouldn't be satisfied:
+#
+#     >>> "3.9.1" < "3.11.1+"
+#     False
+#
+# So in the end, we just strip the trailing `+`, as was done in the days of old
+# for legacy version numbers[5].
+#
+# [1]: https://github.com/astral-sh/uv/issues/1357
+# [2]: https://github.com/python/cpython/issues/99968
+# [3]: https://github.com/pypa/packaging/issues/678#issuecomment-1436033646
+# [4]: https://github.com/astral-sh/uv/issues/1357#issuecomment-1947645243
+# [5]: https://github.com/pypa/packaging/blob/085ff41692b687ae5b0772a55615b69a5b677be9/packaging/version.py#L168-L193
+if len(python_full_version) > 0 and python_full_version[-1] == '+':
+    python_full_version = python_full_version[:-1]
+
 markers = {
     "implementation_name": implementation_name,
     "implementation_version": implementation_version,
@@ -28,7 +65,7 @@ def format_full_version(info):
     "platform_release": platform.release(),
     "platform_system": platform.system(),
     "platform_version": platform.version(),
-    "python_full_version": platform.python_version(),
+    "python_full_version": python_full_version,
     "python_version": ".".join(platform.python_version_tuple()[:2]),
     "sys_platform": sys.platform,
 }