typing: manually add type annotations to `mercurial/vfs.py`

This isn't everything, but hopefully it's close enough to hack on a protocol
class.

mercurial/vfs.py

@@ -1,877 +1,908 b''
 # vfs.py - Mercurial 'vfs' classes
 #
 #  Copyright Olivia Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import annotations
 
 import abc
 import contextlib
 import os
 import shutil
 import stat
 import threading
 import typing
 
 from typing import (
     Any,
+    BinaryIO,
+    Callable,
     Iterable,
     Iterator,
     List,
+    MutableMapping,
     Optional,
     Tuple,
     Type,
     TypeVar,
 )
 
 from .i18n import _
 from . import (
     encoding,
     error,
     pathutil,
     pycompat,
     util,
 )
 
 if typing.TYPE_CHECKING:
+    from . import (
+        ui as uimod,
+    )
+
     _Tbackgroundfilecloser = TypeVar(
         '_Tbackgroundfilecloser', bound='backgroundfilecloser'
     )
     _Tclosewrapbase = TypeVar('_Tclosewrapbase', bound='closewrapbase')
+    _OnErrorFn = Callable[[Exception], Optional[object]]
 
 
-def _avoidambig(path: bytes, oldstat) -> None:
+def _avoidambig(path: bytes, oldstat: util.filestat) -> None:
     """Avoid file stat ambiguity forcibly
 
     This function causes copying ``path`` file, if it is owned by
     another (see issue5418 and issue5584 for detail).
     """
 
     def checkandavoid():
         newstat = util.filestat.frompath(path)
         # return whether file stat ambiguity is (already) avoided
         return not newstat.isambig(oldstat) or newstat.avoidambig(path, oldstat)
 
     if not checkandavoid():
         # simply copy to change owner of path to get privilege to
         # advance mtime (see issue5418)
         util.rename(util.mktempcopy(path), path)
         checkandavoid()
 
 
 class abstractvfs(abc.ABC):
     """Abstract base class; cannot be instantiated"""
 
     # default directory separator for vfs
     #
     # Other vfs code always use `/` and this works fine because python file API
     # abstract the use of `/` and make it work transparently. For consistency
     # vfs will always use `/` when joining. This avoids some confusion in
     # encoded vfs (see issue6546)
     _dir_sep: bytes = b'/'
 
     # TODO: type return, which is util.posixfile wrapped by a proxy
     @abc.abstractmethod
     def __call__(self, path: bytes, mode: bytes = b'rb', **kwargs) -> Any:
         ...
 
     @abc.abstractmethod
-    def _auditpath(self, path: bytes, mode: bytes) -> Any:
+    def _auditpath(self, path: bytes, mode: bytes) -> None:
         ...
 
     @abc.abstractmethod
     def join(self, path: Optional[bytes], *insidef: bytes) -> bytes:
         ...
 
     def tryread(self, path: bytes) -> bytes:
         '''gracefully return an empty string for missing files'''
         try:
             return self.read(path)
         except FileNotFoundError:
             pass
         return b""
 
-    def tryreadlines(self, path: bytes, mode: bytes = b'rb') -> Any:
+    def tryreadlines(self, path: bytes, mode: bytes = b'rb') -> List[bytes]:
         '''gracefully return an empty array for missing files'''
         try:
             return self.readlines(path, mode=mode)
         except FileNotFoundError:
             pass
         return []
 
     @util.propertycache
     def open(self):
         """Open ``path`` file, which is relative to vfs root.
 
         Newly created directories are marked as "not to be indexed by
         the content indexing service", if ``notindexed`` is specified
         for "write" mode access.
         """
         return self.__call__
 
     def read(self, path: bytes) -> bytes:
         with self(path, b'rb') as fp:
             return fp.read()
 
-    def readlines(self, path: bytes, mode: bytes = b'rb') -> Any:
+    def readlines(self, path: bytes, mode: bytes = b'rb') -> List[bytes]:
         with self(path, mode=mode) as fp:
             return fp.readlines()
 
     def write(
-        self, path: bytes, data: bytes, backgroundclose=False, **kwargs
+        self, path: bytes, data: bytes, backgroundclose: bool = False, **kwargs
     ) -> int:
         with self(path, b'wb', backgroundclose=backgroundclose, **kwargs) as fp:
             return fp.write(data)
 
     def writelines(
         self,
         path: bytes,
         data: Iterable[bytes],
         mode: bytes = b'wb',
-        notindexed=False,
+        notindexed: bool = False,
     ) -> None:
         with self(path, mode=mode, notindexed=notindexed) as fp:
             return fp.writelines(data)
 
     def append(self, path: bytes, data: bytes) -> int:
         with self(path, b'ab') as fp:
             return fp.write(data)
 
     def basename(self, path: bytes) -> bytes:
         """return base element of a path (as os.path.basename would do)
 
         This exists to allow handling of strange encoding if needed."""
         return os.path.basename(path)
 
     def chmod(self, path: bytes, mode: int) -> None:
         return os.chmod(self.join(path), mode)
 
     def dirname(self, path: bytes) -> bytes:
         """return dirname element of a path (as os.path.dirname would do)
 
         This exists to allow handling of strange encoding if needed."""
         return os.path.dirname(path)
 
     def exists(self, path: Optional[bytes] = None) -> bool:
         return os.path.exists(self.join(path))
 
-    def fstat(self, fp) -> os.stat_result:
+    def fstat(self, fp: BinaryIO) -> os.stat_result:
         return util.fstat(fp)
 
     def isdir(self, path: Optional[bytes] = None) -> bool:
         return os.path.isdir(self.join(path))
 
     def isfile(self, path: Optional[bytes] = None) -> bool:
         return os.path.isfile(self.join(path))
 
     def islink(self, path: Optional[bytes] = None) -> bool:
         return os.path.islink(self.join(path))
 
     def isfileorlink(self, path: Optional[bytes] = None) -> bool:
         """return whether path is a regular file or a symlink
 
         Unlike isfile, this doesn't follow symlinks."""
         try:
             st = self.lstat(path)
         except OSError:
             return False
         mode = st.st_mode
         return stat.S_ISREG(mode) or stat.S_ISLNK(mode)
 
     def _join(self, *paths: bytes) -> bytes:
         root_idx = 0
         for idx, p in enumerate(paths):
             if os.path.isabs(p) or p.startswith(self._dir_sep):
                 root_idx = idx
         if root_idx != 0:
             paths = paths[root_idx:]
         paths = [p for p in paths if p]
         return self._dir_sep.join(paths)
 
     def reljoin(self, *paths: bytes) -> bytes:
         """join various elements of a path together (as os.path.join would do)
 
         The vfs base is not injected so that path stay relative. This exists
         to allow handling of strange encoding if needed."""
         return self._join(*paths)
 
     def split(self, path: bytes) -> Tuple[bytes, bytes]:
         """split top-most element of a path (as os.path.split would do)
 
         This exists to allow handling of strange encoding if needed."""
         return os.path.split(path)
 
     def lexists(self, path: Optional[bytes] = None) -> bool:
         return os.path.lexists(self.join(path))
 
     def lstat(self, path: Optional[bytes] = None) -> os.stat_result:
         return os.lstat(self.join(path))
 
     def is_mmap_safe(self, path: Optional[bytes] = None) -> bool:
         """return True if it is safe to read a file content as mmap
 
         This focus on the file system aspect of such safety, the application
         logic around that file is not taken into account, so caller need to
         make sure the file won't be truncated in a way that will create SIGBUS
         on access.
 
 
         The initial motivation for this logic is that if mmap is used on NFS
         and somebody deletes the mapped file (e.g. by renaming on top of it),
         then you get SIGBUS, which can be pretty disruptive: we get core dump
         reports, and the process terminates without writing to the blackbox.
 
         Instead, in this situation we prefer to read the file normally.
         The risk of ESTALE in the middle of the read remains, but it's
         smaller because we read sooner and the error should be reported
         just as any other error.
 
         Note that python standard library does not offer the necessary function
         to detect the file stem bits. So this detection rely on compiled bits
         and is not available in pure python.
         """
         # XXX Since we already assume a vfs to address a consistent file system
         # in other location, we could determine the fstype once for the root
         # and cache that value.
         fstype = util.getfstype(self.join(path))
         return fstype is not None and fstype != b'nfs'
 
     def listdir(self, path: Optional[bytes] = None) -> List[bytes]:
         return os.listdir(self.join(path))
 
     def makedir(self, path: Optional[bytes] = None, notindexed=True) -> None:
         return util.makedir(self.join(path), notindexed)
 
     def makedirs(
         self, path: Optional[bytes] = None, mode: Optional[int] = None
     ) -> None:
         return util.makedirs(self.join(path), mode)
 
-    def makelock(self, info, path: bytes) -> None:
+    def makelock(self, info: bytes, path: bytes) -> None:
         return util.makelock(info, self.join(path))
 
     def mkdir(self, path: Optional[bytes] = None) -> None:
         return os.mkdir(self.join(path))
 
     def mkstemp(
         self,
         suffix: bytes = b'',
         prefix: bytes = b'tmp',
         dir: Optional[bytes] = None,
     ) -> Tuple[int, bytes]:
         fd, name = pycompat.mkstemp(
             suffix=suffix, prefix=prefix, dir=self.join(dir)
         )
         dname, fname = util.split(name)
         if dir:
             return fd, os.path.join(dir, fname)
         else:
             return fd, fname
 
+    # TODO: This doesn't match osutil.listdir().  stat=False in pure;
+    #  non-optional bool in cext.  'skip' is bool if we trust cext, or bytes
+    #  going by how pure uses it.  Also, cext returns a custom stat structure.
+    #  from cext.osutil.pyi:
+    #
+    #     path: bytes, st: bool, skip: Optional[bool]
     def readdir(
         self, path: Optional[bytes] = None, stat=None, skip=None
     ) -> Any:
         return util.listdir(self.join(path), stat, skip)
 
     def readlock(self, path: bytes) -> bytes:
         return util.readlock(self.join(path))
 
-    def rename(self, src: bytes, dst: bytes, checkambig=False) -> None:
+    def rename(self, src: bytes, dst: bytes, checkambig: bool = False) -> None:
         """Rename from src to dst
 
         checkambig argument is used with util.filestat, and is useful
         only if destination file is guarded by any lock
         (e.g. repo.lock or repo.wlock).
 
         To avoid file stat ambiguity forcibly, checkambig=True involves
         copying ``src`` file, if it is owned by another. Therefore, use
         checkambig=True only in limited cases (see also issue5418 and
         issue5584 for detail).
         """
         self._auditpath(dst, b'w')
         srcpath = self.join(src)
         dstpath = self.join(dst)
         oldstat = util.filestat.frompath(dstpath) if checkambig else None
 
         util.rename(srcpath, dstpath)
 
         if oldstat and oldstat.stat:
             _avoidambig(dstpath, oldstat)
 
     def readlink(self, path: bytes) -> bytes:
         return util.readlink(self.join(path))
 
     def removedirs(self, path: Optional[bytes] = None) -> None:
         """Remove a leaf directory and all empty intermediate ones"""
         return util.removedirs(self.join(path))
 
     def rmdir(self, path: Optional[bytes] = None) -> None:
         """Remove an empty directory."""
         return os.rmdir(self.join(path))
 
     def rmtree(
-        self, path: Optional[bytes] = None, ignore_errors=False, forcibly=False
+        self,
+        path: Optional[bytes] = None,
+        ignore_errors: bool = False,
+        forcibly: bool = False,
     ) -> None:
         """Remove a directory tree recursively
 
         If ``forcibly``, this tries to remove READ-ONLY files, too.
         """
         if forcibly:
 
-            def onexc(function, path, excinfo):
+            def onexc(function, path: bytes, excinfo):
                 if function is not os.remove:
                     raise
                 # read-only files cannot be unlinked under Windows
                 s = os.stat(path)
                 if (s.st_mode & stat.S_IWRITE) != 0:
                     raise
                 os.chmod(path, stat.S_IMODE(s.st_mode) | stat.S_IWRITE)
                 os.remove(path)
 
         else:
             onexc = None
         try:
             # pytype: disable=wrong-keyword-args
             return shutil.rmtree(
                 self.join(path), ignore_errors=ignore_errors, onexc=onexc
             )
             # pytype: enable=wrong-keyword-args
         except TypeError:  # onexc was introduced in Python 3.12
             return shutil.rmtree(
                 self.join(path), ignore_errors=ignore_errors, onerror=onexc
             )
 
     def setflags(self, path: bytes, l: bool, x: bool) -> None:
         return util.setflags(self.join(path), l, x)
 
     def stat(self, path: Optional[bytes] = None) -> os.stat_result:
         return os.stat(self.join(path))
 
     def unlink(self, path: Optional[bytes] = None) -> None:
         return util.unlink(self.join(path))
 
     def tryunlink(self, path: Optional[bytes] = None) -> bool:
         """Attempt to remove a file, ignoring missing file errors."""
         return util.tryunlink(self.join(path))
 
     def unlinkpath(
-        self, path: Optional[bytes] = None, ignoremissing=False, rmdir=True
+        self,
+        path: Optional[bytes] = None,
+        ignoremissing: bool = False,
+        rmdir: bool = True,
     ) -> None:
         return util.unlinkpath(
             self.join(path), ignoremissing=ignoremissing, rmdir=rmdir
         )
 
-    def utime(self, path: Optional[bytes] = None, t=None) -> None:
+    # TODO: could be Tuple[float, float] too.
+    def utime(
+        self, path: Optional[bytes] = None, t: Optional[Tuple[int, int]] = None
+    ) -> None:
         return os.utime(self.join(path), t)
 
     def walk(
-        self, path: Optional[bytes] = None, onerror=None
+        self, path: Optional[bytes] = None, onerror: Optional[_OnErrorFn] = None
     ) -> Iterator[Tuple[bytes, List[bytes], List[bytes]]]:
         """Yield (dirpath, dirs, files) tuple for each directory under path
 
         ``dirpath`` is relative one from the root of this vfs. This
         uses ``os.sep`` as path separator, even you specify POSIX
         style ``path``.
 
         "The root of this vfs" is represented as empty ``dirpath``.
         """
         root = os.path.normpath(self.join(None))
         # when dirpath == root, dirpath[prefixlen:] becomes empty
         # because len(dirpath) < prefixlen.
         prefixlen = len(pathutil.normasprefix(root))
         for dirpath, dirs, files in os.walk(self.join(path), onerror=onerror):
             yield (dirpath[prefixlen:], dirs, files)
 
     @contextlib.contextmanager
     def backgroundclosing(
-        self, ui, expectedcount=-1
+        self, ui: uimod.ui, expectedcount: int = -1
     ) -> Iterator[Optional[backgroundfilecloser]]:
         """Allow files to be closed asynchronously.
 
         When this context manager is active, ``backgroundclose`` can be passed
         to ``__call__``/``open`` to result in the file possibly being closed
         asynchronously, on a background thread.
         """
         # Sharing backgroundfilecloser between threads is complex and using
         # multiple instances puts us at risk of running out of file descriptors
         # only allow to use backgroundfilecloser when in main thread.
         if threading.current_thread() is not threading.main_thread():
             yield
             return
         vfs = getattr(self, 'vfs', self)
         if getattr(vfs, '_backgroundfilecloser', None):
             raise error.Abort(
                 _(b'can only have 1 active background file closer')
             )
 
         with backgroundfilecloser(ui, expectedcount=expectedcount) as bfc:
             try:
                 vfs._backgroundfilecloser = (
                     bfc  # pytype: disable=attribute-error
                 )
                 yield bfc
             finally:
                 vfs._backgroundfilecloser = (
                     None  # pytype: disable=attribute-error
                 )
 
-    def register_file(self, path) -> None:
+    def register_file(self, path: bytes) -> None:
         """generic hook point to lets fncache steer its stew"""
 
 
 class vfs(abstractvfs):
     """Operate files relative to a base directory
 
     This class is used to hide the details of COW semantics and
     remote file access from higher level code.
 
     'cacheaudited' should be enabled only if (a) vfs object is short-lived, or
     (b) the base directory is managed by hg and considered sort-of append-only.
     See pathutil.pathauditor() for details.
     """
 
+    createmode: Optional[int]
+
     def __init__(
         self,
         base: bytes,
-        audit=True,
-        cacheaudited=False,
-        expandpath=False,
-        realpath=False,
+        audit: bool = True,
+        cacheaudited: bool = False,
+        expandpath: bool = False,
+        realpath: bool = False,
     ) -> None:
         if expandpath:
             base = util.expandpath(base)
         if realpath:
             base = os.path.realpath(base)
         self.base = base
         self._audit = audit
         if audit:
             self.audit = pathutil.pathauditor(self.base, cached=cacheaudited)
         else:
             self.audit = lambda path, mode=None: True
         self.createmode = None
         self._trustnlink = None
         self.options = {}
 
     @util.propertycache
     def _cansymlink(self) -> bool:
         return util.checklink(self.base)
 
     @util.propertycache
-    def _chmod(self):
+    def _chmod(self) -> bool:
         return util.checkexec(self.base)
 
-    def _fixfilemode(self, name) -> None:
+    def _fixfilemode(self, name: bytes) -> None:
         if self.createmode is None or not self._chmod:
             return
         os.chmod(name, self.createmode & 0o666)
 
-    def _auditpath(self, path, mode) -> None:
+    def _auditpath(self, path: bytes, mode: bytes) -> None:
         if self._audit:
             if os.path.isabs(path) and path.startswith(self.base):
                 path = os.path.relpath(path, self.base)
             r = util.checkosfilename(path)
             if r:
                 raise error.Abort(b"%s: %r" % (r, path))
             self.audit(path, mode=mode)
 
     def isfileorlink_checkdir(
-        self, dircache, path: Optional[bytes] = None
+        self,
+        dircache: MutableMapping[bytes, bool],
+        path: Optional[bytes] = None,
     ) -> bool:
         """return True if the path is a regular file or a symlink and
         the directories along the path are "normal", that is
         not symlinks or nested hg repositories.
 
         Ignores the `_audit` setting, and checks the directories regardless.
         `dircache` is used to cache the directory checks.
         """
+        # TODO: Should be a None check on 'path', or shouldn't default to None
+        #  because of the immediate call to util.localpath().
         try:
             for prefix in pathutil.finddirs_rev_noroot(util.localpath(path)):
                 if prefix in dircache:
                     res = dircache[prefix]
                 else:
                     res = pathutil.pathauditor._checkfs_exists(
                         self.base, prefix, path
                     )
                     dircache[prefix] = res
                 if not res:
                     return False
         except (OSError, error.Abort):
             return False
         return self.isfileorlink(path)
 
     def __call__(
         self,
         path: bytes,
         mode: bytes = b"rb",
-        atomictemp=False,
-        notindexed=False,
-        backgroundclose=False,
-        checkambig=False,
-        auditpath=True,
-        makeparentdirs=True,
-    ) -> Any:
+        atomictemp: bool = False,
+        notindexed: bool = False,
+        backgroundclose: bool = False,
+        checkambig: bool = False,
+        auditpath: bool = True,
+        makeparentdirs: bool = True,
+    ) -> Any:  # TODO: should be BinaryIO if util.atomictempfile can be coersed
         """Open ``path`` file, which is relative to vfs root.
 
         By default, parent directories are created as needed. Newly created
         directories are marked as "not to be indexed by the content indexing
         service", if ``notindexed`` is specified for "write" mode access.
         Set ``makeparentdirs=False`` to not create directories implicitly.
 
         If ``backgroundclose`` is passed, the file may be closed asynchronously.
         It can only be used if the ``self.backgroundclosing()`` context manager
         is active. This should only be specified if the following criteria hold:
 
         1. There is a potential for writing thousands of files. Unless you
            are writing thousands of files, the performance benefits of
            asynchronously closing files is not realized.
         2. Files are opened exactly once for the ``backgroundclosing``
            active duration and are therefore free of race conditions between
            closing a file on a background thread and reopening it. (If the
            file were opened multiple times, there could be unflushed data
            because the original file handle hasn't been flushed/closed yet.)
 
         ``checkambig`` argument is passed to atomictempfile (valid
         only for writing), and is useful only if target file is
         guarded by any lock (e.g. repo.lock or repo.wlock).
 
         To avoid file stat ambiguity forcibly, checkambig=True involves
         copying ``path`` file opened in "append" mode (e.g. for
         truncation), if it is owned by another. Therefore, use
         combination of append mode and checkambig=True only in limited
         cases (see also issue5418 and issue5584 for detail).
         """
         if auditpath:
             self._auditpath(path, mode)
         f = self.join(path)
 
         if b"b" not in mode:
             mode += b"b"  # for that other OS
 
         nlink = -1
         if mode not in (b'r', b'rb'):
             dirname, basename = util.split(f)
             # If basename is empty, then the path is malformed because it points
             # to a directory. Let the posixfile() call below raise IOError.
             if basename:
                 if atomictemp:
                     if makeparentdirs:
                         util.makedirs(dirname, self.createmode, notindexed)
                     return util.atomictempfile(
                         f, mode, self.createmode, checkambig=checkambig
                     )
                 try:
                     if b'w' in mode:
                         util.unlink(f)
                         nlink = 0
                     else:
                         # nlinks() may behave differently for files on Windows
                         # shares if the file is open.
                         with util.posixfile(f):
                             nlink = util.nlinks(f)
                             if nlink < 1:
                                 nlink = 2  # force mktempcopy (issue1922)
                 except FileNotFoundError:
                     nlink = 0
                     if makeparentdirs:
                         util.makedirs(dirname, self.createmode, notindexed)
                 if nlink > 0:
                     if self._trustnlink is None:
                         self._trustnlink = nlink > 1 or util.checknlink(f)
                     if nlink > 1 or not self._trustnlink:
                         util.rename(util.mktempcopy(f), f)
         fp = util.posixfile(f, mode)
         if nlink == 0:
             self._fixfilemode(f)
 
         if checkambig:
             if mode in (b'r', b'rb'):
                 raise error.Abort(
                     _(
                         b'implementation error: mode %s is not'
                         b' valid for checkambig=True'
                     )
                     % mode
                 )
             fp = checkambigatclosing(fp)
 
         if (
             backgroundclose
             and threading.current_thread() is threading.main_thread()
         ):
             if (
                 not self._backgroundfilecloser  # pytype: disable=attribute-error
             ):
                 raise error.Abort(
                     _(
                         b'backgroundclose can only be used when a '
                         b'backgroundclosing context manager is active'
                     )
                 )
 
             fp = delayclosedfile(
                 fp,
                 self._backgroundfilecloser,  # pytype: disable=attribute-error
             )
 
         return fp
 
     def symlink(self, src: bytes, dst: bytes) -> None:
         self.audit(dst)
         linkname = self.join(dst)
         util.tryunlink(linkname)
 
         util.makedirs(os.path.dirname(linkname), self.createmode)
 
         if self._cansymlink:
             try:
                 os.symlink(src, linkname)
             except OSError as err:
                 raise OSError(
                     err.errno,
                     _(b'could not symlink to %r: %s')
                     % (src, encoding.strtolocal(err.strerror)),
                     linkname,
                 )
         else:
             self.write(dst, src)
 
     def join(self, path: Optional[bytes], *insidef: bytes) -> bytes:
         if path:
             parts = [self.base, path]
             parts.extend(insidef)
             return self._join(*parts)
         else:
             return self.base
 
 
 opener: Type[vfs] = vfs
 
 
 class proxyvfs(abstractvfs, abc.ABC):
-    def __init__(self, vfs: "vfs"):
+    def __init__(self, vfs: vfs) -> None:
         self.vfs = vfs
 
     @property
-    def createmode(self):
+    def createmode(self) -> Optional[int]:
         return self.vfs.createmode
 
-    def _auditpath(self, path, mode) -> None:
+    def _auditpath(self, path: bytes, mode: bytes) -> None:
         return self.vfs._auditpath(path, mode)
 
     @property
     def options(self):
         return self.vfs.options
 
     @options.setter
     def options(self, value):
         self.vfs.options = value
 
     @property
     def audit(self):
         return self.vfs.audit
 
 
 class filtervfs(proxyvfs, abstractvfs):
     '''Wrapper vfs for filtering filenames with a function.'''
 
-    def __init__(self, vfs: "vfs", filter):
+    def __init__(self, vfs: vfs, filter) -> None:
         proxyvfs.__init__(self, vfs)
         self._filter = filter
 
+    # TODO: The return type should be BinaryIO
     def __call__(self, path: bytes, *args, **kwargs) -> Any:
         return self.vfs(self._filter(path), *args, **kwargs)
 
     def join(self, path: Optional[bytes], *insidef: bytes) -> bytes:
         if path:
             return self.vfs.join(self._filter(self.vfs.reljoin(path, *insidef)))
         else:
             return self.vfs.join(path)
 
 
 filteropener: Type[filtervfs] = filtervfs
 
 
 class readonlyvfs(proxyvfs):
     '''Wrapper vfs preventing any writing.'''
 
-    def __init__(self, vfs: "vfs"):
+    def __init__(self, vfs: vfs) -> None:
         proxyvfs.__init__(self, vfs)
 
+    # TODO: The return type should be BinaryIO
     def __call__(self, path: bytes, mode: bytes = b'rb', *args, **kw) -> Any:
         if mode not in (b'r', b'rb'):
             raise error.Abort(_(b'this vfs is read only'))
         return self.vfs(path, mode, *args, **kw)
 
     def join(self, path: Optional[bytes], *insidef: bytes) -> bytes:
         return self.vfs.join(path, *insidef)
 
 
 class closewrapbase(abc.ABC):
     """Base class of wrapper, which hooks closing
 
     Do not instantiate outside the vfs layer.
     """
 
     def __init__(self, fh) -> None:
         object.__setattr__(self, '_origfh', fh)
 
-    def __getattr__(self, attr) -> Any:
+    def __getattr__(self, attr: str) -> Any:
         return getattr(self._origfh, attr)
 
-    def __setattr__(self, attr, value) -> None:
+    def __setattr__(self, attr: str, value: Any) -> None:
         return setattr(self._origfh, attr, value)
 
-    def __delattr__(self, attr) -> None:
+    def __delattr__(self, attr: str) -> None:
         return delattr(self._origfh, attr)
 
     def __enter__(self: _Tclosewrapbase) -> _Tclosewrapbase:
         self._origfh.__enter__()
         return self
 
     @abc.abstractmethod
     def __exit__(self, exc_type, exc_value, exc_tb) -> None:
         ...
 
     @abc.abstractmethod
     def close(self) -> None:
         ...
 
 
 class delayclosedfile(closewrapbase):
     """Proxy for a file object whose close is delayed.
 
     Do not instantiate outside the vfs layer.
     """
 
     def __init__(self, fh, closer) -> None:
         super(delayclosedfile, self).__init__(fh)
         object.__setattr__(self, '_closer', closer)
 
     def __exit__(self, exc_type, exc_value, exc_tb) -> None:
         self._closer.close(self._origfh)
 
     def close(self) -> None:
         self._closer.close(self._origfh)
 
 
 class backgroundfilecloser:
     """Coordinates background closing of file handles on multiple threads."""
 
-    def __init__(self, ui, expectedcount=-1) -> None:
+    def __init__(self, ui: uimod.ui, expectedcount: int = -1) -> None:
         self._running = False
         self._entered = False
         self._threads = []
         self._threadexception = None
 
         # Only Windows/NTFS has slow file closing. So only enable by default
         # on that platform. But allow to be enabled elsewhere for testing.
         defaultenabled = pycompat.iswindows
         enabled = ui.configbool(b'worker', b'backgroundclose', defaultenabled)
 
         if not enabled:
             return
 
         # There is overhead to starting and stopping the background threads.
         # Don't do background processing unless the file count is large enough
         # to justify it.
         minfilecount = ui.configint(b'worker', b'backgroundcloseminfilecount')
         # FUTURE dynamically start background threads after minfilecount closes.
         # (We don't currently have any callers that don't know their file count)
         if expectedcount > 0 and expectedcount < minfilecount:
             return
 
         maxqueue = ui.configint(b'worker', b'backgroundclosemaxqueue')
         threadcount = ui.configint(b'worker', b'backgroundclosethreadcount')
 
         ui.debug(
             b'starting %d threads for background file closing\n' % threadcount
         )
 
         self._queue = pycompat.queue.Queue(maxsize=maxqueue)
         self._running = True
 
         for i in range(threadcount):
             t = threading.Thread(target=self._worker, name='backgroundcloser')
             self._threads.append(t)
             t.start()
 
     def __enter__(self: _Tbackgroundfilecloser) -> _Tbackgroundfilecloser:
         self._entered = True
         return self
 
     def __exit__(self, exc_type, exc_value, exc_tb) -> None:
         self._running = False
 
         # Wait for threads to finish closing so open files don't linger for
         # longer than lifetime of context manager.
         for t in self._threads:
             t.join()
 
     def _worker(self) -> None:
         """Main routine for worker thread."""
         while True:
             try:
                 fh = self._queue.get(block=True, timeout=0.100)
                 # Need to catch or the thread will terminate and
                 # we could orphan file descriptors.
                 try:
                     fh.close()
                 except Exception as e:
                     # Stash so can re-raise from main thread later.
                     self._threadexception = e
             except pycompat.queue.Empty:
                 if not self._running:
                     break
 
     def close(self, fh) -> None:
         """Schedule a file for closing."""
         if not self._entered:
             raise error.Abort(
                 _(b'can only call close() when context manager active')
             )
 
         # If a background thread encountered an exception, raise now so we fail
         # fast. Otherwise, we may potentially go on for minutes until the error
         # is acted on.
         if self._threadexception:
             e = self._threadexception
             self._threadexception = None
             raise e
 
         # If we're not actively running, close synchronously.
         if not self._running:
             fh.close()
             return
 
         self._queue.put(fh, block=True, timeout=None)
 
 
 class checkambigatclosing(closewrapbase):
     """Proxy for a file object, to avoid ambiguity of file stat
 
     See also util.filestat for detail about "ambiguity of file stat".
 
     This proxy is useful only if the target file is guarded by any
     lock (e.g. repo.lock or repo.wlock)
 
     Do not instantiate outside the vfs layer.
     """
 
     def __init__(self, fh) -> None:
         super(checkambigatclosing, self).__init__(fh)
         object.__setattr__(self, '_oldstat', util.filestat.frompath(fh.name))
 
     def _checkambig(self) -> None:
         oldstat = self._oldstat
         if oldstat.stat:
             _avoidambig(self._origfh.name, oldstat)
 
     def __exit__(self, exc_type, exc_value, exc_tb) -> None:
         self._origfh.__exit__(exc_type, exc_value, exc_tb)
         self._checkambig()
 
     def close(self) -> None:
         self._origfh.close()
         self._checkambig()