Avoid impossible impossible minversion requirement

Fixes: #2414

Author: ssbarnea

docs/changelog/2414.bugfix.rst

@@ -0,0 +1 @@
+Avoid impossible minversion version requirements. - by :user:`ssbarnea`.

src/tox/provision.py

@@ -75,6 +75,14 @@ def provision(state: State) -> int | bool:
 
     def add_tox_requires_min_version(requires: list[Requirement]) -> list[Requirement]:
         min_version: Version = state.conf.core["min_version"]
+        # If own version can be a development one or a pre-release, we need to
+        # to only use its base_version for requirements, or pip will never be
+        # able to find a version that is compatible with the requirement.
+        # See https://github.com/tox-dev/tox/issues/2414
+        if min_version.is_devrelease or min_version.is_prerelease:  # noqa: SC200
+            # So we build a PEP 440 version out of the base ones.
+            # https://peps.python.org/pep-0440/#implicit-pre-release-number
+            min_version = Version(min_version.base_version + "a0")
         requires.append(Requirement(f"tox >= {min_version.public}"))
         return requires
 

tests/test_provision.py

@@ -13,6 +13,7 @@
 import pytest
 from filelock import FileLock
 from packaging.requirements import Requirement
+from packaging.version import Version
 
 from tox import __version__
 from tox.pytest import Index, IndexServer, MonkeyPatch, TempPathFactory, ToxProjectCreator
@@ -188,5 +189,7 @@ def test_provision_no_recreate_json(tox_project: ToxProjectCreator) -> None:
     assert msg in result.out
     with (project.path / "out.json").open() as file_handler:
         requires = json.load(file_handler)
-    version = __version__.split("+")[0]
+    # __version__ could be something like 4.0.0b3.dev23+g50e62f93 so we still  # noqa: SC100
+    # need to sanitize it to keep the base and add "a0"  # noqa: SC100
+    version = Version(__version__).base_version + "a0"
     assert requires == {"minversion": version, "requires": ["p", f"tox>={version}"]}