Add failing test for marker eval on versions

This commit adds test cases to cover version-to-version and
non-version-to-version marker evaluation, according to PEP 508,
Environment Markers. https://peps.python.org/pep-0508/#environment-markers

Marker evaluation currently throws an InvalidVersion error when the rhs
is a valid version but the lhs is not. For example, consider the
dependency:

> Requires-Dist: typing-extensions (>=4,<5) ; extra == "v8"

The extra name "v8" is both a valid version and extra name. During
evaluation of this requirement, the LHS of the marker can take on the
value "", or some other extra name, which are not valid versions.

When this situation occurs, the comparison fails by throwing
InvalidVersion, rather then returning False. This is causing pip to
crash when attempting to install a package with such a requirement.

Currently, just one of these added cases is failing - the
"quux" == "v8" case.

I've also added two cases to document the (perhaps surprising) behaviour
that is a result of the PEP 508 spec requiring normalized version
comparison to apply to extras when both sides are valid versions.

Author: h4l

tests/test_markers.py

@@ -314,6 +314,14 @@ def test_environment_with_extra_none(self):
                 {"extra": "different__punctuation_is_EQUAL"},
                 True,
             ),
+            # extra name that is also a valid version - version comparison applies
+            # if both sides are valid versions
+            ("extra == 'v8'", {"extra": "quux"}, False),
+            ("extra == 'v8'", {"extra": "v8"}, True),
+            # LHS and RHS are valid versions, so equality uses normalized version
+            ("extra == 'v8-dev'", {"extra": "v8-dev.0"}, True),
+            # Only one side is a valid version, so values are not normalized as versions
+            ("extra == 'v-8-dev'", {"extra": "v-8-dev.0"}, False),
         ],
     )
     def test_evaluates(self, marker_string, environment, expected):