[WIP] GH-65238: Preserve trailing slash in pathlib

Doc/library/pathlib.rst

@@ -145,6 +145,15 @@ we also call *flavours*:
       >>> PureWindowsPath('c:/Windows', '/Program Files')
       PureWindowsPath('c:/Program Files')
 
+   At most one trailing slash is kept::
+
+      >>> PurePath('foo//')
+      PurePosixPath('foo/')
+
+   .. versionchanged:: 3.13
+      A trailing slash is now retained, as it is meaningful to path
+      resolution.
+
    Spurious slashes and single dots are collapsed, but double dots (``'..'``)
    and leading double slashes (``'//'``) are not, since this would change the
    meaning of a path for various reasons (e.g. symbolic links, UNC paths)::
@@ -153,8 +162,8 @@ we also call *flavours*:
       PurePosixPath('foo/bar')
       >>> PurePath('//foo/bar')
       PurePosixPath('//foo/bar')
-      >>> PurePath('foo/./bar')
-      PurePosixPath('foo/bar')
+      >>> PurePath('foo/./bar/.')
+      PurePosixPath('foo/bar/')
       >>> PurePath('foo/../bar')
       PurePosixPath('foo/../bar')
 
@@ -184,7 +193,7 @@ we also call *flavours*:
    filesystem paths, including `UNC paths`_::
 
       >>> PureWindowsPath('c:/Program Files/')
-      PureWindowsPath('c:/Program Files')
+      PureWindowsPath('c:/Program Files/')
       >>> PureWindowsPath('//server/share/file')
       PureWindowsPath('//server/share/file')
 
@@ -376,6 +385,21 @@ Pure paths provide the following methods and properties:
       '\\\\host\\share\\'
 
 
+.. attribute:: PurePath.has_trailing_sep
+
+   Whether the path has a trailing slash after its :attr:`name`::
+
+      >>> PurePosixPath('foo/bar/').has_trailing_sep
+      True
+
+   If the path has no name, this property is false::
+
+      >>> PureWindowsPath('c:/').has_trailing_sep
+      False
+
+   .. versionadded:: 3.13
+
+
 .. attribute:: PurePath.parents
 
    An immutable sequence providing access to the logical ancestors of
@@ -614,6 +638,10 @@ Pure paths provide the following methods and properties:
       Support for the recursive wildcard "``**``" was added. In previous
       versions, it acted like the non-recursive wildcard "``*``".
 
+   .. versionchanged:: 3.13
+      Matching now considers whether the path and *pattern* end with path
+      separators.
+
 
 .. method:: PurePath.relative_to(other, walk_up=False)
 
@@ -719,6 +747,41 @@ Pure paths provide the following methods and properties:
       PureWindowsPath('README')
 
 
+.. method:: PurePath.with_trailing_sep()
+
+   Return a new path with a trailing slash after its :attr:`name`. If the
+   original path doesn't have a name, :exc:`ValueError` is raised::
+
+      >>> p = PureWindowsPath('c:/windows')
+      >>> p.with_trailing_sep()
+      PureWindowsPath('c:/windows/')
+      >>> p = PureWindowsPath('c:/')
+      >>> p.with_trailing_sep()
+      Traceback (most recent call last):
+        File "<stdin>", line 1, in <module>
+          p.with_trailing_sep()
+          ~~~~~~~~~~~~~~~~~~~^^
+        File "/home/barney/projects/cpython/Lib/pathlib.py", line 459, in with_trailing_sep
+          raise ValueError(f"{self!r} has an empty name")
+      ValueError: PureWindowsPath('c:/') has an empty name
+
+   .. versionadded:: 3.13
+
+
+.. method:: PurePath.without_trailing_sep()
+
+   Return a new path without a slash after its :attr:`name`, if any::
+
+      >>> p = PureWindowsPath('c:/windows/')
+      >>> p.without_trailing_sep()
+      PureWindowsPath('c:/windows')
+      >>> p = PureWindowsPath('c:/')
+      >>> p.without_trailing_sep()
+      PureWindowsPath('c:/')
+
+   .. versionadded:: 3.13
+
+
 .. method:: PurePath.with_segments(*pathsegments)
 
    Create a new path object of the same type by combining the given
@@ -1020,6 +1083,11 @@ call fails (for example because the path doesn't exist).
       future Python release, patterns with this ending will match both files
       and directories. Add a trailing slash to match only directories.
 
+   .. versionchanged:: 3.13
+      Returns paths with trailing path separators if *pattern* also ends with
+      a pathname components separator (:data:`~os.sep` or :data:`~os.altsep`).
+
+
 .. method:: Path.group(*, follow_symlinks=True)
 
    Return the name of the group owning the file. :exc:`KeyError` is raised

Lib/pathlib/__init__.py

@@ -89,7 +89,8 @@ def __init__(self, *args):
                         "argument should be a str or an os.PathLike "
                         "object where __fspath__ returns a str, "
                         f"not {type(path).__name__!r}")
-                paths.append(path)
+                if path:
+                    paths.append(path)
         # Avoid calling super().__init__, as an optimisation
         self._raw_paths = paths
         self._resolving = False
@@ -287,7 +288,7 @@ def absolute(self):
             return self
         if self.root:
             drive = os.path.splitroot(os.getcwd())[0]
-            return self._from_parsed_parts(drive, self.root, self._tail)
+            return self._from_parsed_parts(drive, self.root, self._tail, self.has_trailing_sep)
         if self.drive:
             # There is a CWD on each drive-letter drive.
             cwd = os.path.abspath(self.drive)
@@ -304,10 +305,10 @@ def absolute(self):
             return result
         drive, root, rel = os.path.splitroot(cwd)
         if not rel:
-            return self._from_parsed_parts(drive, root, self._tail)
+            return self._from_parsed_parts(drive, root, self._tail, self.has_trailing_sep)
         tail = rel.split(self.pathmod.sep)
         tail.extend(self._tail)
-        return self._from_parsed_parts(drive, root, tail)
+        return self._from_parsed_parts(drive, root, tail, self.has_trailing_sep)
 
     def resolve(self, strict=False):
         """
@@ -454,8 +455,10 @@ def expanduser(self):
             homedir = os.path.expanduser(self._tail[0])
             if homedir[:1] == "~":
                 raise RuntimeError("Could not determine home directory.")
-            drv, root, tail = self._parse_path(homedir)
-            return self._from_parsed_parts(drv, root, tail + self._tail[1:])
+            drv, root, tail, _ = self._parse_path(homedir)
+            tail.extend(self._tail[1:])
+            has_trailing_sep = self.has_trailing_sep and bool(tail)
+            return self._from_parsed_parts(drv, root, tail, has_trailing_sep)
 
         return self