interfaces: introduce and use a protocol class for the `base85` module

See f2832de2a46c for details when this was done for the `bdiff` module.

It looks like PEP-688 removed the special casing of `bytes` being a standin
for any type of `ByteString`, and defines a `typing.Buffer` class (with a
backport in `typing_extensions` for Python prior to 3.12).  There's been a lot
of churn in this area with pytype, but recent versions of pytype and PyCharm
recognize this, and e.g. have `mercurial.node.hex()` defined as:

    from typing_extensions import Buffer

    def hex(data: Buffer, sep: str | bytes = ..., bytes_per_sep: int = ...) -> bytes

This covers `bytes`, `bytearray`, and `memoryview` by default.  Both of the C
functions here use `y#` to parse the arguments, which means the arg is a
byte-like object[2], so the args would appear to be better typed as `Buffer`.
However, pytype has a bug that prevents using this from `typing_extensions`[3],
and mypy complained `Unsupported left operand type for + ("memoryview")` in the
pure module on line 37 (meaning it's only a subset of `Buffer`).  So hold off on
changing any of that for now.

[1] https://peps.python.org/pep-0688/#no-special-meaning-for-bytes
[2] https://docs.python.org/3/glossary.html#term-bytes-like-object
[3] https://github.com/google/pytype/issues/1772

mercurial/interfaces/modules.py

@@ -23,6 +23,16 if typing.TYPE_CHECKING:
     """The signature of `bdiff.blocks()` and `bdiff.xdiffblocks()`."""
 
 
+class Base85(Protocol):
+    """A Protocol class for the various base85 module implementations."""
+
+    def b85encode(self, text: bytes, pad: bool = False) -> bytes:
+        """encode text in base85 format"""
+
+    def b85decode(self, text: bytes) -> bytes:
+        """decode base85-encoded text"""
+
+
 class BDiff(Protocol):
     """A Protocol class for the various bdiff module implementations."""
 

mercurial/util.py

@@ -70,6 +70,9 from . import (
     typelib,
     urllibcompat,
 )
+from .interfaces import (
+    modules as intmod,
+)
 from .utils import (
     compression,
     hashutil,
@@ -87,7 +90,7 assert [
 ]
 
 
-base85 = policy.importmod('base85')
+base85: intmod.Base85 = policy.importmod('base85')
 osutil = policy.importmod('osutil')
 
 b85decode = base85.b85decode