WIP

myvenv/lib/python3.10/site-packages/werkzeug/filesystem.py

@@ -0,0 +1,55 @@
+import codecs
+import sys
+import typing as t
+import warnings
+
+# We do not trust traditional unixes.
+has_likely_buggy_unicode_filesystem = (
+    sys.platform.startswith("linux") or "bsd" in sys.platform
+)
+
+
+def _is_ascii_encoding(encoding: t.Optional[str]) -> bool:
+    """Given an encoding this figures out if the encoding is actually ASCII (which
+    is something we don't actually want in most cases). This is necessary
+    because ASCII comes under many names such as ANSI_X3.4-1968.
+    """
+    if encoding is None:
+        return False
+    try:
+        return codecs.lookup(encoding).name == "ascii"
+    except LookupError:
+        return False
+
+
+class BrokenFilesystemWarning(RuntimeWarning, UnicodeWarning):
+    """The warning used by Werkzeug to signal a broken filesystem. Will only be
+    used once per runtime."""
+
+
+_warned_about_filesystem_encoding = False
+
+
+def get_filesystem_encoding() -> str:
+    """Returns the filesystem encoding that should be used. Note that this is
+    different from the Python understanding of the filesystem encoding which
+    might be deeply flawed. Do not use this value against Python's string APIs
+    because it might be different. See :ref:`filesystem-encoding` for the exact
+    behavior.
+
+    The concept of a filesystem encoding in generally is not something you
+    should rely on. As such if you ever need to use this function except for
+    writing wrapper code reconsider.
+    """
+    global _warned_about_filesystem_encoding
+    rv = sys.getfilesystemencoding()
+    if has_likely_buggy_unicode_filesystem and not rv or _is_ascii_encoding(rv):
+        if not _warned_about_filesystem_encoding:
+            warnings.warn(
+                "Detected a misconfigured UNIX filesystem: Will use"
+                f" UTF-8 as filesystem encoding instead of {rv!r}",
+                BrokenFilesystemWarning,
+            )
+            _warned_about_filesystem_encoding = True
+        return "utf-8"
+    return rv