Vendorize LegacyVersion behavior for patterns like "2.4-openbsd"

We still need those to work - not to break pypi conformance, but since
we use this for tmux versions.

Author: tony

libtmux/_compat.py

@@ -28,6 +28,98 @@ def str_from_console(s):
 
 
 try:
-    from packaging.version import LegacyVersion as LooseVersion, Version
+    import re
+
+    from packaging.version import Version, _BaseVersion
+
+    ###
+    ### Legacy support for LooseVersion / LegacyVersion, e.g. 2.4-openbsd
+    ### https://github.com/pypa/packaging/blob/21.3/packaging/version.py#L106-L115
+    ### License: BSD, Accessed: Jan 14th, 2022
+    ###
+
+    _legacy_version_component_re = re.compile(r"(\d+ | [a-z]+ | \.| -)", re.VERBOSE)
+    _legacy_version_replacement_map = {
+        "pre": "c",
+        "preview": "c",
+        "-": "final-",
+        "rc": "c",
+        "dev": "@",
+    }
+
+    def _parse_version_parts(s):
+        # type: (str) -> Iterator[str]
+        for part in _legacy_version_component_re.split(s):
+            part = _legacy_version_replacement_map.get(part, part)
+
+            if not part or part == ".":
+                continue
+
+            if part[:1] in "0123456789":
+                # pad for numeric comparison
+                yield part.zfill(8)
+            else:
+                yield "*" + part
+
+        # ensure that alpha/beta/candidate are before final
+        yield "*final"
+
+    def _legacy_cmpkey(version):
+        # type: (str) -> LegacyCmpKey
+
+        # We hardcode an epoch of -1 here. A PEP 440 version can only have a epoch
+        # greater than or equal to 0. This will effectively put the LegacyVersion,
+        # which uses the defacto standard originally implemented by setuptools,
+        # as before all PEP 440 versions.
+        epoch = -1
+
+        # This scheme is taken from pkg_resources.parse_version setuptools prior to
+        # it's adoption of the packaging library.
+        parts = []  # type: List[str]
+        for part in _parse_version_parts(version.lower()):
+            if part.startswith("*"):
+                # remove "-" before a prerelease tag
+                if part < "*final":
+                    while parts and parts[-1] == "*final-":
+                        parts.pop()
+
+                # remove trailing zeros from each series of numeric parts
+                while parts and parts[-1] == "00000000":
+                    parts.pop()
+
+            parts.append(part)
+
+        return epoch, tuple(parts)
+
+    class LegacyVersion(_BaseVersion):
+        def __init__(self, version):
+            # type: (str) -> None
+            self._version = str(version)
+            self._key = _legacy_cmpkey(self._version)
+
+        def __str__(self):
+            # type: () -> str
+            return self._version
+
+        def __repr__(self):
+            # type: () -> str
+            return "<LegacyVersion({0})>".format(repr(str(self)))
+
+        @property
+        def public(self):
+            # type: () -> str
+            return self._version
+
+        @property
+        def base_version(self):
+            # type: () -> str
+            return self._version
+
+        @property
+        def epoch(self):
+            # type: () -> int
+            return -1
+
+    LooseVersion = LegacyVersion
 except ImportError:
     from distutils.version import LooseVersion, Version