mergestate: use an early return for trivial merges
`filemerge.filemerge()` returns `None` if no merge was needed because
the two sides were identical. I'd like to move that to the
caller. This is a little refactoring to prepare for that.
Differential Revision: https://phab.mercurial-scm.org/D12153
from typing import (
List,
Tuple,
)
version: int
def bdiff(a: bytes, b: bytes): bytes
def blocks(a: bytes, b: bytes) -> List[Tuple[int, int, int, int]]: ...
def fixws(s: bytes, allws: bool) -> bytes: ...
def splitnewlines(text: bytes) -> List[bytes]: ...
def xdiffblocks(a: bytes, b: bytes) -> List[Tuple[int, int, int, int]]: ...