Prevent sys.prefix from leaking into child process on macOS (#1648)

Author: cjolowicz

docs/changelog/1643.bugfix.rst

@@ -0,0 +1,2 @@
+Fix cross interpreter support when the host python sets ``sys.base_executable`` based on ``__PYVENV_LAUNCHER__`` -
+by :user:`cjolowicz`

src/virtualenv/discovery/cached_py_info.py

@@ -101,12 +101,21 @@ def _get_fs_path():
 def _run_subprocess(cls, exe):
     resolved_path = Path(os.path.abspath(__file__)).parent / "py_info.py"
     with ensure_file_on_disk(resolved_path) as resolved_path:
+
         cmd = [exe, "-s", str(resolved_path)]
+        # prevent sys.prefix from leaking into the child process - see https://bugs.python.org/issue22490
+        env = os.environ.copy()
+        env.pop("__PYVENV_LAUNCHER__", None)
 
         logging.debug("get interpreter info via cmd: %s", LogCmd(cmd))
         try:
             process = Popen(
-                cmd, universal_newlines=True, stdin=subprocess.PIPE, stderr=subprocess.PIPE, stdout=subprocess.PIPE
+                cmd,
+                universal_newlines=True,
+                stdin=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+                stdout=subprocess.PIPE,
+                env=env,
             )
             out, err = process.communicate()
             code = process.returncode