Handle KeyError for unknown resources

When importlib.resources (or the importlib_resources backport) uses
zipfile.Path in the Python 3.8/3.9 stdlib (rather than the zipp
backport), we get KeyError rather than a FileNotFoundError if a resource
does not exist. See https://bugs.python.org/issue43063.

We work around this by re-raising a KeyError as FileNotFoundError.

Fixes #6086

(cherry picked from commit 9313523ae144f350ce5c930e735ba9257c34067e)

1 files changed, 19 insertions, 2 deletions

diff --git a/qutebrowser/utils/utils.py b/qutebrowser/utils/utils.py
index 5e4c418ff..a52c5fada 100644
--- a/qutebrowser/utils/utils.py
+++ b/qutebrowser/utils/utils.py
@@ -192,6 +192,21 @@ def _resource_path(filename: str) -> pathlib.Path:
     return importlib_resources.files(qutebrowser) / filename
 
 
+@contextlib.contextmanager
+def _resource_keyerror_workaround() -> Iterator[None]:
+    """Re-raise KeyErrors as FileNotFoundErrors.
+
+    WORKAROUND for zipfile.Path resources raising KeyError when a file was notfound:
+    https://bugs.python.org/issue43063
+
+    Only needed for Python 3.8 and 3.9.
+    """
+    try:
+        yield
+    except KeyError as e:
+        raise FileNotFoundError(str(e))
+
+
 def _glob_resources(
     resource_path: pathlib.Path,
     subdir: str,
@@ -240,7 +255,8 @@ def read_file(filename: str) -> str:
         return _resource_cache[filename]
 
     path = _resource_path(filename)
-    return path.read_text(encoding='utf-8')
+    with _resource_keyerror_workaround():
+        return path.read_text(encoding='utf-8')
 
 
 def read_file_binary(filename: str) -> bytes:
@@ -253,7 +269,8 @@ def read_file_binary(filename: str) -> bytes:
         The file contents as a bytes object.
     """
     path = _resource_path(filename)
-    return path.read_bytes()
+    with _resource_keyerror_workaround():
+        return path.read_bytes()
 
 
 def parse_version(version: str) -> VersionNumber: