typing: add type hints to pycompat.bytestr The problem with leaving pytype to its own devices here was that for functions that returned a bytestr, pytype inferred `Union[bytes, int]`. It now accepts that it can be treated as plain bytes. I wasn't able to figure out the arg type for `__getitem__`- `SupportsIndex` (which PyCharm indicated is how the superclass function is typed) got flagged: File "/mnt/c/Users/Matt/hg/mercurial/pycompat.py", line 236, in __getitem__: unsupported operand type(s) for item retrieval: bytestr and SupportsIndex [unsupported-operands] Function __getitem__ on bytestr expects int But some caller got flagged when I marked it as `int`. There's some minor spillover problems elsewhere- pytype doesn't seem to recognize that `bytes.startswith()` can optionally take a 3rd and 4th arg, so those few places have the warning disabled. It also flags where the tar API is being abused, but that would be a tricky refactor (and would require typing extensions until py3.7 is dropped), so disable those too.

--- a/mercurial/archival.py	Wed Dec 14 01:38:52 2022 -0500
+++ b/mercurial/archival.py	Wed Dec 14 01:51:33 2022 -0500
@@ -154,9 +154,14 @@
                 )
                 self.fileobj = gzfileobj
                 return (
+                    # taropen() wants Literal['a', 'r', 'w', 'x'] for the mode,
+                    # but Literal[] is only available in 3.8+ without the
+                    # typing_extensions backport.
+                    # pytype: disable=wrong-arg-types
                     tarfile.TarFile.taropen(  # pytype: disable=attribute-error
                         name, pycompat.sysstr(mode), gzfileobj
                     )
+                    # pytype: enable=wrong-arg-types
                 )
             else:
                 try: