branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
from typing import (
AnyStr,
IO,
List,
Optional,
Sequence,
)
version: int
class stat:
st_dev: int
st_mode: int
st_nlink: int
st_size: int
st_mtime: int
st_ctime: int
def listdir(path: bytes, st: bool, skip: Optional[bool]) -> List[stat]: ...
def posixfile(name: AnyStr, mode: bytes, buffering: int) -> IO: ...
def statfiles(names: Sequence[bytes]) -> List[stat]: ...
def setprocname(name: bytes) -> None: ...
def getfstype(path: bytes) -> bytes: ...
def getfsmountpoint(path: bytes) -> bytes: ...
def unblocksignal(sig: int) -> None: ...
def isgui() -> bool: ...