GH-130614: pathlib ABCs: revise test suite for readable paths (#131018)

Test `pathlib.types._ReadablePath` in a dedicated test module. These tests
cover `ReadableZipPath`, `ReadableLocalPath` and `Path`, where the former
two classes are implementations of `_ReadablePath` for use in tests.

Lib/test/test_pathlib/support/zip_path.py

@@ -0,0 +1,278 @@
+"""
+Implementation of ReadablePath for zip file members, for use in pathlib tests.
+
+ZipPathGround is also defined here. It helps establish the "ground truth"
+about zip file members in tests.
+"""
+
+import errno
+import io
+import pathlib.types
+import posixpath
+import stat
+import zipfile
+from stat import S_IFMT, S_ISDIR, S_ISREG, S_ISLNK
+
+
+class ZipPathGround:
+    can_symlink = True
+
+    def __init__(self, path_cls):
+        self.path_cls = path_cls
+
+    def setup(self, local_suffix=""):
+        return self.path_cls(zip_file=zipfile.ZipFile(io.BytesIO(), "w"))
+
+    def teardown(self, root):
+        root.zip_file.close()
+
+    def create_file(self, path, data=b''):
+        path.zip_file.writestr(str(path), data)
+
+    def create_dir(self, path):
+        path.zip_file.mkdir(str(path))
+
+    def create_symlink(self, path, target):
+        zip_info = zipfile.ZipInfo(str(path))
+        zip_info.external_attr = stat.S_IFLNK << 16
+        path.zip_file.writestr(zip_info, target.encode())
+
+    def create_hierarchy(self, p):
+        # Add regular files
+        self.create_file(p.joinpath('fileA'), b'this is file A\n')
+        self.create_file(p.joinpath('dirB/fileB'), b'this is file B\n')
+        self.create_file(p.joinpath('dirC/fileC'), b'this is file C\n')
+        self.create_file(p.joinpath('dirC/dirD/fileD'), b'this is file D\n')
+        self.create_file(p.joinpath('dirC/novel.txt'), b'this is a novel\n')
+        # Add symlinks
+        self.create_symlink(p.joinpath('linkA'), 'fileA')
+        self.create_symlink(p.joinpath('linkB'), 'dirB')
+        self.create_symlink(p.joinpath('dirA/linkC'), '../dirB')
+        self.create_symlink(p.joinpath('brokenLink'), 'non-existing')
+        self.create_symlink(p.joinpath('brokenLinkLoop'), 'brokenLinkLoop')
+
+    def readtext(self, p):
+        with p.zip_file.open(str(p), 'r') as f:
+            f = io.TextIOWrapper(f)
+            return f.read()
+
+    def readbytes(self, p):
+        with p.zip_file.open(str(p), 'r') as f:
+            return f.read()
+
+    readlink = readtext
+
+    def isdir(self, p):
+        path_str = str(p) + "/"
+        return path_str in p.zip_file.NameToInfo
+
+    def isfile(self, p):
+        info = p.zip_file.NameToInfo.get(str(p))
+        if info is None:
+            return False
+        return not stat.S_ISLNK(info.external_attr >> 16)
+
+    def islink(self, p):
+        info = p.zip_file.NameToInfo.get(str(p))
+        if info is None:
+            return False
+        return stat.S_ISLNK(info.external_attr >> 16)
+
+
+class MissingZipPathInfo:
+    """
+    PathInfo implementation that is used when a zip file member is missing.
+    """
+    __slots__ = ()
+
+    def exists(self, follow_symlinks=True):
+        return False
+
+    def is_dir(self, follow_symlinks=True):
+        return False
+
+    def is_file(self, follow_symlinks=True):
+        return False
+
+    def is_symlink(self):
+        return False
+
+    def resolve(self):
+        return self
+
+
+missing_zip_path_info = MissingZipPathInfo()
+
+
+class ZipPathInfo:
+    """
+    PathInfo implementation for an existing zip file member.
+    """
+    __slots__ = ('zip_file', 'zip_info', 'parent', 'children')
+
+    def __init__(self, zip_file, parent=None):
+        self.zip_file = zip_file
+        self.zip_info = None
+        self.parent = parent or self
+        self.children = {}
+
+    def exists(self, follow_symlinks=True):
+        if follow_symlinks and self.is_symlink():
+            return self.resolve().exists()
+        return True
+
+    def is_dir(self, follow_symlinks=True):
+        if follow_symlinks and self.is_symlink():
+            return self.resolve().is_dir()
+        elif self.zip_info is None:
+            return True
+        elif fmt := S_IFMT(self.zip_info.external_attr >> 16):
+            return S_ISDIR(fmt)
+        else:
+            return self.zip_info.filename.endswith('/')
+
+    def is_file(self, follow_symlinks=True):
+        if follow_symlinks and self.is_symlink():
+            return self.resolve().is_file()
+        elif self.zip_info is None:
+            return False
+        elif fmt := S_IFMT(self.zip_info.external_attr >> 16):
+            return S_ISREG(fmt)
+        else:
+            return not self.zip_info.filename.endswith('/')
+
+    def is_symlink(self):
+        if self.zip_info is None:
+            return False
+        elif fmt := S_IFMT(self.zip_info.external_attr >> 16):
+            return S_ISLNK(fmt)
+        else:
+            return False
+
+    def resolve(self, path=None, create=False, follow_symlinks=True):
+        """
+        Traverse zip hierarchy (parents, children and symlinks) starting
+        from this PathInfo. This is called from three places:
+
+        - When a zip file member is added to ZipFile.filelist, this method
+          populates the ZipPathInfo tree (using create=True).
+        - When ReadableZipPath.info is accessed, this method is finds a
+          ZipPathInfo entry for the path without resolving any final symlink
+          (using follow_symlinks=False)
+        - When ZipPathInfo methods are called with follow_symlinks=True, this
+          method resolves any symlink in the final path position.
+        """
+        link_count = 0
+        stack = path.split('/')[::-1] if path else []
+        info = self
+        while True:
+            if info.is_symlink() and (follow_symlinks or stack):
+                link_count += 1
+                if link_count >= 40:
+                    return missing_zip_path_info  # Symlink loop!
+                path = info.zip_file.read(info.zip_info).decode()
+                stack += path.split('/')[::-1] if path else []
+                info = info.parent
+
+            if stack:
+                name = stack.pop()
+            else:
+                return info
+
+            if name == '..':
+                info = info.parent
+            elif name and name != '.':
+                if name not in info.children:
+                    if create:
+                        info.children[name] = ZipPathInfo(info.zip_file, info)
+                    else:
+                        return missing_zip_path_info  # No such child!
+                info = info.children[name]
+
+
+class ZipFileList:
+    """
+    `list`-like object that we inject as `ZipFile.filelist`. We maintain a
+    tree of `ZipPathInfo` objects representing the zip file members.
+    """
+
+    __slots__ = ('tree', '_items')
+
+    def __init__(self, zip_file):
+        self.tree = ZipPathInfo(zip_file)
+        self._items = []
+        for item in zip_file.filelist:
+            self.append(item)
+
+    def __len__(self):
+        return len(self._items)
+
+    def __iter__(self):
+        return iter(self._items)
+
+    def append(self, item):
+        self._items.append(item)
+        self.tree.resolve(item.filename, create=True).zip_info = item
+
+
+class ReadableZipPath(pathlib.types._ReadablePath):
+    """
+    Simple implementation of a ReadablePath class for .zip files.
+    """
+
+    __slots__ = ('_segments', 'zip_file')
+    parser = posixpath
+
+    def __init__(self, *pathsegments, zip_file):
+        self._segments = pathsegments
+        self.zip_file = zip_file
+        if not isinstance(zip_file.filelist, ZipFileList):
+            zip_file.filelist = ZipFileList(zip_file)
+
+    def __hash__(self):
+        return hash((str(self), self.zip_file))
+
+    def __eq__(self, other):
+        if not isinstance(other, ReadableZipPath):
+            return NotImplemented
+        return str(self) == str(other) and self.zip_file is other.zip_file
+
+    def __str__(self):
+        if not self._segments:
+            return ''
+        return self.parser.join(*self._segments)
+
+    def __repr__(self):
+        return f'{type(self).__name__}({str(self)!r}, zip_file={self.zip_file!r})'
+
+    def with_segments(self, *pathsegments):
+        return type(self)(*pathsegments, zip_file=self.zip_file)
+
+    @property
+    def info(self):
+        tree = self.zip_file.filelist.tree
+        return tree.resolve(str(self), follow_symlinks=False)
+
+    def __open_rb__(self, buffering=-1):
+        info = self.info.resolve()
+        if not info.exists():
+            raise FileNotFoundError(errno.ENOENT, "File not found", self)
+        elif info.is_dir():
+            raise IsADirectoryError(errno.EISDIR, "Is a directory", self)
+        return self.zip_file.open(info.zip_info, 'r')
+
+    def iterdir(self):
+        info = self.info.resolve()
+        if not info.exists():
+            raise FileNotFoundError(errno.ENOENT, "File not found", self)
+        elif not info.is_dir():
+            raise NotADirectoryError(errno.ENOTDIR, "Not a directory", self)
+        return (self / name for name in info.children)
+
+    def readlink(self):
+        info = self.info
+        if not info.exists():
+            raise FileNotFoundError(errno.ENOENT, "File not found", self)
+        elif not info.is_symlink():
+            raise OSError(errno.EINVAL, "Not a symlink", self)
+        return self.with_segments(self.zip_file.read(info.zip_info).decode())