env: prevent warning from being emitted on venv creation

src/build/env.py

@@ -92,7 +92,12 @@ def __enter__(self) -> IsolatedEnv:
 
         :return: The isolated build environment
         """
-        self._path = tempfile.mkdtemp(prefix='build-env-')
+        # Call ``realpath`` to prevent spurious warning from being emitted
+        # that the venv location has changed on Windows. The username is
+        # DOS-encoded in the output of tempfile - the location is the same
+        # but the representation of it is different, which confuses venv.
+        # Ref: https://bugs.python.org/issue46171
+        self._path = os.path.realpath(tempfile.mkdtemp(prefix='build-env-'))
         try:
             # use virtualenv when available (as it's faster than venv)
             if _should_use_virtualenv():

tests/test_env.py

@@ -112,7 +112,7 @@ def test_isolated_env_log(mocker, caplog, package_test_flit):
         ('INFO', 'Installing packages in isolated environment... (something)'),
     ]
     if sys.version_info >= (3, 8):  # stacklevel
-        assert [(record.lineno) for record in caplog.records] == [105, 102, 193]
+        assert [(record.lineno) for record in caplog.records] == [105, 107, 198]
 
 
 @pytest.mark.isolated