typing: run `merge-pyi` on `mercurial/vfs.py` The *.pyi file was generated with pytype 2023.11.21. There were a few things here that were wrong (e.g. `writelines()` takes an `Iterable[bytes]`, not `bytes`, or inexplicable errors like importing several of the vfs classes from this very module), and those changes have been dropped manually here.

typing: add type annotations to `mercurial.util.makelock()` This bubbles up into the `vfs` classes, so get this out of the way.

util: avoid a leaked file descriptor in `util.makelock()` exceptional case

typing: add type annotations to the `mercurial.util.filestat` class It's referenced in the `vfs` classes, so get this out of the way to help there. The `TypeVar` definition and its usage was copied from the existing `util.pyi` file.

vfs: do minor copyediting on comments and doc strings These were flagged by PyCharm, so clear them from the gutter.

vfs: simplify the `abstractvfs.rename()` implementation PyCharm was yapping about `util.rename()` not returning anything, because it is typed to return `None`, but the value was captured and returned after calling `_avoidambig()`. Instead, drop all of that, unconditionally rename, and then call `_avoidambig()` if appropriate. While we're here, convert the ersatz ternary operator into a modern one to help pytype. When a variable is initialized the old way, pytype tends to assign the type of the LHS of the `and`. In this case, that's a bool, and it will get confused that bool doesn't have a `stat` attribute once this method gets more type annotations. (Currently it thinks the `checkambig` arg is `Any`, so it doesn't care.)

vfs: use @abstractmethod instead of homebrewing abstract methods The latter confuses PyCharm after adding more type annotations when, for example, `abstractvfs.rename()` calls `_auditpath()`- the latter unconditionally raised an error, so PyCharm thought the code that came after is unreachable. It also tricked pytype into marking the return type as `Never`, which isn't available until Python 3.11 (outside of `typing_extensions`). This also avoid PyCharm warnings that the call to the superclass constructor was missed (it couldn't be called because it raised an error to prevent instantiation). The statichttprepo module needed to be given an override for one of the abstract methods, so that it can be instantiated. In `abstractvfs`, this method is only called by `rename()`, so I think we can leave this empty. We raise an error in case somebody accidentally calls it in the future- it would have raised this same error prior to this change. I couldn't wrangle `import-checker.py` into accepting importing `ABC` and `abstractmethod`- for each subsequent import, it reports something like: stdlib import "contextlib" follows local import: abc I suspect the problem is that near the `if fullname != '__future__'` check, if the module doesn't fall into the error case, `seenlocal` gets set to the module name. That causes it to be treated like a local module on the next iteration, even though it is in `stdlib_modules`.

vfs: modernize the detection of the main thread There weren't a lot of good choices when py27 was supported, but starting with py34, `threading.main_thread()` is available. This gets us away from an undocumented, internal symbol, and drops a pytype suppression statement. It is also apparently no longer reliable after a process fork.[1][2] [1] https://stackoverflow.com/a/23207116 [2] https://github.com/python/cpython/blob/v3.6.3/Lib/threading.py#L1334