Add type annotations to _pytest.pathlib

At least the ones I was sure of.

src/_pytest/pathlib.py

@@ -1,7 +1,6 @@
 import atexit
 import fnmatch
 import itertools
-import operator
 import os
 import shutil
 import sys
@@ -13,6 +12,11 @@ from os.path import expandvars
 from os.path import isabs
 from os.path import sep
 from posixpath import sep as posix_sep
+from typing import Iterable
+from typing import Iterator
+from typing import Set
+from typing import TypeVar
+from typing import Union
 
 from _pytest.warning_types import PytestWarning
 
@@ -26,10 +30,15 @@ __all__ = ["Path", "PurePath"]
 
 LOCK_TIMEOUT = 60 * 60 * 3
 
-get_lock_path = operator.methodcaller("joinpath", ".lock")
+
+_AnyPurePath = TypeVar("_AnyPurePath", bound=PurePath)
 
 
-def ensure_reset_dir(path):
+def get_lock_path(path: _AnyPurePath) -> _AnyPurePath:
+    return path.joinpath(".lock")
+
+
+def ensure_reset_dir(path: Path) -> None:
     """
     ensures the given path is an empty directory
     """
@@ -38,7 +47,7 @@ def ensure_reset_dir(path):
     path.mkdir()
 
 
-def on_rm_rf_error(func, path: str, exc, *, start_path) -> bool:
+def on_rm_rf_error(func, path: str, exc, *, start_path: Path) -> bool:
     """Handles known read-only errors during rmtree.
 
     The returned value is used only by our own tests.
@@ -71,7 +80,7 @@ def on_rm_rf_error(func, path: str, exc, *, start_path) -> bool:
     # Chmod + retry.
     import stat
 
-    def chmod_rw(p: str):
+    def chmod_rw(p: str) -> None:
         mode = os.stat(p).st_mode
         os.chmod(p, mode | stat.S_IRUSR | stat.S_IWUSR)
 
@@ -90,7 +99,7 @@ def on_rm_rf_error(func, path: str, exc, *, start_path) -> bool:
     return True
 
 
-def rm_rf(path: Path):
+def rm_rf(path: Path) -> None:
     """Remove the path contents recursively, even if some elements
     are read-only.
     """
@@ -98,7 +107,7 @@ def rm_rf(path: Path):
     shutil.rmtree(str(path), onerror=onerror)
 
 
-def find_prefixed(root, prefix):
+def find_prefixed(root: Path, prefix: str) -> Iterator[Path]:
     """finds all elements in root that begin with the prefix, case insensitive"""
     l_prefix = prefix.lower()
     for x in root.iterdir():
@@ -106,7 +115,7 @@ def find_prefixed(root, prefix):
             yield x
 
 
-def extract_suffixes(iter, prefix):
+def extract_suffixes(iter: Iterable[PurePath], prefix: str) -> Iterator[str]:
     """
     :param iter: iterator over path names
     :param prefix: expected prefix of the path names
@@ -117,13 +126,13 @@ def extract_suffixes(iter, prefix):
         yield p.name[p_len:]
 
 
-def find_suffixes(root, prefix):
+def find_suffixes(root: Path, prefix: str) -> Iterator[str]:
     """combines find_prefixes and extract_suffixes
     """
     return extract_suffixes(find_prefixed(root, prefix), prefix)
 
 
-def parse_num(maybe_num):
+def parse_num(maybe_num) -> int:
     """parses number path suffixes, returns -1 on error"""
     try:
         return int(maybe_num)
@@ -131,7 +140,9 @@ def parse_num(maybe_num):
         return -1
 
 
-def _force_symlink(root, target, link_to):
+def _force_symlink(
+    root: Path, target: Union[str, PurePath], link_to: Union[str, Path]
+) -> None:
     """helper to create the current symlink
 
     it's full of race conditions that are reasonably ok to ignore
@@ -151,7 +162,7 @@ def _force_symlink(root, target, link_to):
         pass
 
 
-def make_numbered_dir(root, prefix):
+def make_numbered_dir(root: Path, prefix: str) -> Path:
     """create a directory with an increased number as suffix for the given prefix"""
     for i in range(10):
         # try up to 10 times to create the folder
@@ -172,7 +183,7 @@ def make_numbered_dir(root, prefix):
         )
 
 
-def create_cleanup_lock(p):
+def create_cleanup_lock(p: Path) -> Path:
     """crates a lock to prevent premature folder cleanup"""
     lock_path = get_lock_path(p)
     try:
@@ -189,11 +200,11 @@ def create_cleanup_lock(p):
         return lock_path
 
 
-def register_cleanup_lock_removal(lock_path, register=atexit.register):
+def register_cleanup_lock_removal(lock_path: Path, register=atexit.register):
     """registers a cleanup function for removing a lock, by default on atexit"""
     pid = os.getpid()
 
-    def cleanup_on_exit(lock_path=lock_path, original_pid=pid):
+    def cleanup_on_exit(lock_path: Path = lock_path, original_pid: int = pid) -> None:
         current_pid = os.getpid()
         if current_pid != original_pid:
             # fork
@@ -206,7 +217,7 @@ def register_cleanup_lock_removal(lock_path, register=atexit.register):
     return register(cleanup_on_exit)
 
 
-def maybe_delete_a_numbered_dir(path):
+def maybe_delete_a_numbered_dir(path: Path) -> None:
     """removes a numbered directory if its lock can be obtained and it does not seem to be in use"""
     lock_path = None
     try:
@@ -232,7 +243,7 @@ def maybe_delete_a_numbered_dir(path):
                 pass
 
 
-def ensure_deletable(path, consider_lock_dead_if_created_before):
+def ensure_deletable(path: Path, consider_lock_dead_if_created_before: float) -> bool:
     """checks if a lock exists and breaks it if its considered dead"""
     if path.is_symlink():
         return False
@@ -251,13 +262,13 @@ def ensure_deletable(path, consider_lock_dead_if_created_before):
             return False
 
 
-def try_cleanup(path, consider_lock_dead_if_created_before):
+def try_cleanup(path: Path, consider_lock_dead_if_created_before: float) -> None:
     """tries to cleanup a folder if we can ensure it's deletable"""
     if ensure_deletable(path, consider_lock_dead_if_created_before):
         maybe_delete_a_numbered_dir(path)
 
 
-def cleanup_candidates(root, prefix, keep):
+def cleanup_candidates(root: Path, prefix: str, keep: int) -> Iterator[Path]:
     """lists candidates for numbered directories to be removed - follows py.path"""
     max_existing = max(map(parse_num, find_suffixes(root, prefix)), default=-1)
     max_delete = max_existing - keep
@@ -269,7 +280,9 @@ def cleanup_candidates(root, prefix, keep):
             yield path
 
 
-def cleanup_numbered_dir(root, prefix, keep, consider_lock_dead_if_created_before):
+def cleanup_numbered_dir(
+    root: Path, prefix: str, keep: int, consider_lock_dead_if_created_before: float
+) -> None:
     """cleanup for lock driven numbered directories"""
     for path in cleanup_candidates(root, prefix, keep):
         try_cleanup(path, consider_lock_dead_if_created_before)
@@ -277,7 +290,9 @@ def cleanup_numbered_dir(root, prefix, keep, consider_lock_dead_if_created_befor
         try_cleanup(path, consider_lock_dead_if_created_before)
 
 
-def make_numbered_dir_with_cleanup(root, prefix, keep, lock_timeout):
+def make_numbered_dir_with_cleanup(
+    root: Path, prefix: str, keep: int, lock_timeout: float
+) -> Path:
     """creates a numbered dir with a cleanup lock and removes old ones"""
     e = None
     for i in range(10):
@@ -311,7 +326,7 @@ def resolve_from_str(input, root):
         return root.joinpath(input)
 
 
-def fnmatch_ex(pattern, path):
+def fnmatch_ex(pattern: str, path) -> bool:
     """FNMatcher port from py.path.common which works with PurePath() instances.
 
     The difference between this algorithm and PurePath.match() is that the latter matches "**" glob expressions
@@ -346,6 +361,6 @@ def fnmatch_ex(pattern, path):
     return fnmatch.fnmatch(name, pattern)
 
 
-def parts(s):
+def parts(s: str) -> Set[str]:
     parts = s.split(sep)
     return {sep.join(parts[: i + 1]) or sep for i in range(len(parts))}