Restore limited <major>.<minor> environment name support (#3319)

Author: gaborbernat

docs/changelog.rst

@@ -9,7 +9,7 @@ v4.17.0 (2024-08-05)
 
 Features - 4.17.0
 ~~~~~~~~~~~~~~~~~
-- Add "graalpy" prefix as a supported base python (:issue:`3312`)
+- Add ``graalpy`` prefix as a supported base python (:issue:`3312`)
 - Add :ref:`on_platform` core configuration holding the tox platform and do not install package when exec an environment
   - by :user:`gaborbernat`. (:issue:`3315`)
 
@@ -69,7 +69,7 @@ Bugfixes - 4.14.2
 
 Improved Documentation - 4.14.2
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Removed unused line from the 'fresh_subprocess' documentation. (:issue:`3241`)
+- Removed unused line from the ``fresh_subprocess`` documentation. (:issue:`3241`)
 
 v4.14.1 (2024-03-06)
 --------------------
@@ -216,9 +216,9 @@ v4.7.0 (2023-08-08)
 
 Features - 4.7.0
 ~~~~~~~~~~~~~~~~
-- Make --hashseed default to PYTHONHASHSEED, if defined - by :user:`paravoid`.
+- Make ``--hashseed`` default to ``PYTHONHASHSEED``, if defined - by :user:`paravoid`.
   The main motivation for this is to able to set the hash seed when building the
-  documentation with "tox -e docs", and thus avoid embedding a random value in
+  documentation with ``tox -e docs``, and thus avoid embedding a random value in
   the tox documentation for --help. This caused documentation builds to fail to
   build reproducibly. (:issue:`2942`)
 

docs/changelog/2849.bugfix.rst

@@ -0,0 +1 @@
+Support for running ``-e <major>.<minor>`` has been lost, fixing it - by :user:`gaborbernat`.

src/tox/tox_env/python/api.py

@@ -56,6 +56,7 @@ def version_dot(self) -> str:
     """,
     re.VERBOSE,
 )
+PY_FACTORS_RE_EXPLICIT_VERSION = re.compile(r"^(?P<version>[2-9]\.[0-9]+)$")
 
 
 class Python(ToxEnv, ABC):
@@ -142,10 +143,14 @@ def default_base_python(self, conf: Config, env_name: str | None) -> list[str]:
     @classmethod
     def extract_base_python(cls, env_name: str) -> str | None:
         candidates: list[str] = []
-        for factor in env_name.split("-"):
-            match = PY_FACTORS_RE.match(factor)
-            if match:
-                candidates.append(factor)
+        match = PY_FACTORS_RE_EXPLICIT_VERSION.match(env_name)
+        if match:
+            candidates.append(env_name)
+        else:
+            for factor in env_name.split("-"):
+                match = PY_FACTORS_RE.match(factor)
+                if match:
+                    candidates.append(factor)
         if candidates:
             if len(candidates) > 1:
                 msg = f"conflicting factors {', '.join(candidates)} in {env_name}"

tests/tox_env/python/test_python_api.py

@@ -100,6 +100,9 @@ def test_diff_msg_no_diff() -> None:
         ("5", None),
         ("2000", None),
         ("4000", None),
+        ("3.10", "3.10"),
+        ("3.9", "3.9"),
+        ("2.7", "2.7"),
     ],
     ids=lambda a: "|".join(a) if isinstance(a, list) else str(a),
 )