bugfix: Also skip the gitcache script run by a Python interpreter

CHANGELOG.md

@@ -11,6 +11,10 @@
   named `git` was skipped, so that renaming or hard-linking the gitcache executable to `git` resulted in an
   infinite recursion. As the check now compares the candidates with the gitcache executable, a symlink pointing to
   the real git command is no longer skipped either.
+- Bugfix: Also skip the gitcache script when it is run by a Python interpreter, as in a pip installation. There,
+  `sys.executable` is the interpreter, so a `git` symlink to the installed `gitcache` script was returned as the
+  real git command whenever no `RealGit` was configured, e.g. with `HOME` pointing to a fresh directory, and each
+  call spawned itself until the system ran out of memory.
 - Bugfix: Keep the user of `ssh://` and scp-style URLs when normalizing URLs and stripping credentials. The
   user of an SSH URL is part of the address, not a secret. Dropping it left mirrors created from SSH URLs
   unable to authenticate on `gitcache -u` and whenever the same repository was reached through an HTTPS URL

src/git_cache/config.py

@@ -80,6 +80,19 @@ def has_git_lfs_cmd() -> bool:
     return has_git_lfs_cmd.has_git_lfs  # type: ignore
 
 
+def _is_gitcache_executable(candidate: str) -> bool:
+    """Check whether the given path is the running gitcache executable.
+
+    A frozen gitcache is ``sys.executable``. A pip-installed gitcache is a script
+    started by the Python interpreter, so ``sys.executable`` is the interpreter and
+    the script is ``sys.argv[0]``.
+    """
+    own_paths = [sys.executable]
+    if sys.argv and sys.argv[0]:
+        own_paths.append(sys.argv[0])
+    return any(os.path.exists(own) and os.path.samefile(candidate, own) for own in own_paths)
+
+
 def find_git() -> str:
     """Locate the real git command.
 
@@ -95,7 +108,7 @@ def find_git() -> str:
             candidate = os.path.join(candidate, cmd)
             if not os.path.exists(candidate) or not os.access(candidate, os.X_OK):
                 continue
-            if os.path.samefile(candidate, sys.executable):
+            if _is_gitcache_executable(candidate):
                 continue
             return candidate
 

test/unittests/test_git_cache_config.py

@@ -193,10 +193,11 @@ def _create_executable(directory, name):
         os.chmod(path, 0o755)
         return path
 
-    def _find_git(self, executable):
+    def _find_git(self, executable, argv0=None):
         """Call find_git() as the given executable with the gitcache dir in front of the real git dir."""
         path = os.path.pathsep.join([self.gitcache_dir, self.real_git_dir])
-        with mock.patch.object(sys, "executable", executable), mockenv(PATH=path):
+        argv = [argv0 if argv0 is not None else executable]
+        with mock.patch.object(sys, "executable", executable), mock.patch.object(sys, "argv", argv), mockenv(PATH=path):
             return git_cache.config.find_git()
 
     def test_gitcache_executable(self):
@@ -221,6 +222,21 @@ def test_skip_git_executable(self):
         gitcache_as_git = self._create_executable(self.gitcache_dir, self.GIT_CMD)
         self.assertEqual(self._find_git(gitcache_as_git), self.real_git_cmd)
 
+    def test_skip_git_symlink_to_script(self):
+        """git_cache.config.find_git: Skip a symlink to a gitcache script run by a separate interpreter."""
+        interpreter = self._create_executable(self.tmp_dir, "python")
+        git_symlink = os.path.join(self.gitcache_dir, self.GIT_CMD)
+        try:
+            os.symlink(self.gitcache_cmd, git_symlink)
+        except OSError:
+            self.skipTest("This system does not allow the creation of symlinks.")
+        self.assertEqual(self._find_git(interpreter, argv0=git_symlink), self.real_git_cmd)
+
+    def test_skip_without_argv0(self):
+        """git_cache.config.find_git: Ignore an empty sys.argv[0]."""
+        interpreter = self._create_executable(self.tmp_dir, "python")
+        self.assertEqual(self._find_git(interpreter, argv0=""), self.real_git_cmd)
+
 
 # -----------------------------------------------------------------------------
 # EOF