fix(runfiles): assume main repository on Windows

With any Python version on Windows, `RUNFILES_*` environment variables
still point to an intermediate stage path instead of the module path,
causing `CurrentRepository()` to raise a `ValueError` since
`rules_python` v1.8.0:
```
ValueError: C:\Users\bot\AppData\Local\Temp\Bazel.runfiles_gh34ij5_\runfiles\+_repo_rules+cpython\my_script.py does not lie under the runfiles root C:/cache/ab1cdef2/execroot/_main/bazel-out/x64_windows-fastbuild/bin/external/+_repo_rules+cpython/install.exe.runfiles
```

This was not the case with `rules_python` v1.7.0. The issue stems from
bazel-contrib#3086 which, by eliminating a wrong assumption, also brought a stricter
behavior.

Since bazel-contrib#3086 came up with a corresponding workaround in
`//tests/runtime_env_toolchain:toolchain_runs_test`, the proposed fix
simply consists in moving it to `CurrentRepository()`, thus adding
another case to the workaround introduced by bazel-contrib#1634 for Python < 3.11
- so assuming the main repository on Windows as well.

Removing the workaround from `CurrentRepository()`, would make the test
fail as follows:
```
==================== Test output for //tests/runtime_env_toolchain:toolchain_runs_test:
E
======================================================================
ERROR: test_ran (__main__.RunTest.test_ran)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\user\AppData\Local\Temp\Bazel.runfiles_1f08smy6\runfiles\_main\tests\runtime_env_toolchain\toolchain_runs_test.py", line 13, in test_ran
    settings_path = rf.Rlocation(
        "rules_python/tests/support/current_build_settings.json"
    )
  File "C:\Users\user\AppData\Local\Temp\Bazel.runfiles_1f08smy6\runfiles\_main\python\runfiles\runfiles.py", line 306, in Rlocation
    source_repo = self.CurrentRepository(frame=2)
  File "C:\Users\user\AppData\Local\Temp\Bazel.runfiles_1f08smy6\runfiles\_main\python\runfiles\runfiles.py", line 404, in CurrentRepository
    raise ValueError(
    ...<3 lines>...
    )
ValueError: C:\Users\user\AppData\Local\Temp\Bazel.runfiles_1f08smy6\runfiles\_main\tests\runtime_env_toolchain\toolchain_runs_test.py does not lie under the runfiles root c:\users\user\_bazel_user\cxxeswjo\execroot\_main\bazel-out\x64_windows-fastbuild-st-c530e4918e48\bin\tests\runtime_env_toolchain\toolchain_runs_test.exe.runfiles
```

Author: rdesgroppes

CHANGELOG.md

@@ -75,6 +75,7 @@ END_UNRELEASED_TEMPLATE
 
 {#v0-0-0-fixed}
 ### Fixed
+* (runfiles) Fixed `CurrentRepository()` raising `ValueError` on Windows.
 * (tests) No more coverage warnings are being printed if there are no sources.
   ([#2762](https://github.com/bazel-contrib/rules_python/issues/2762))
 * (gazelle) Ancestor `conftest.py` files are added in addition to sibling `conftest.py`.

python/runfiles/runfiles.py

@@ -389,11 +389,15 @@ def CurrentRepository(self, frame: int = 1) -> str:
             # located in the main repository.
             # With Python 3.11 and higher, the Python launcher sets
             # PYTHONSAFEPATH, which prevents this behavior.
+            # On Windows, the current toolchain being used has a buggy zip file
+            # bootstrap, which leaves RUNFILES_DIR pointing at the first stage
+            # path and not the module path. In this case too, assume that the
+            # module is located in the main repository.
             # TODO: This doesn't cover the case of a script being run from an
             #       external repository, which could be heuristically detected
             #       by parsing the script's path.
             if (
-                sys.version_info.minor <= 10
+                (sys.version_info.minor <= 10 or sys.platform == "win32")
                 and sys.path[0] != self._python_runfiles_root
             ):
                 return ""

tests/runtime_env_toolchain/toolchain_runs_test.py

@@ -10,17 +10,9 @@
 class RunTest(unittest.TestCase):
     def test_ran(self):
         rf = runfiles.Create()
-        try:
-            settings_path = rf.Rlocation(
-                "rules_python/tests/support/current_build_settings.json"
-            )
-        except ValueError as e:
-            # The current toolchain being used has a buggy zip file bootstrap, which
-            # leaves RUNFILES_DIR pointing at the first stage path and not the module
-            # path.
-            if platform.system() != "Windows" or "does not lie under the runfiles root" not in str(e):
-                raise e
-            settings_path = "./tests/support/current_build_settings.json"
+        settings_path = rf.Rlocation(
+            "rules_python/tests/support/current_build_settings.json"
+        )
 
         settings = json.loads(pathlib.Path(settings_path).read_text())