Use vendored packaging to canonicalize requirements

This makes the METADATA file from bdist_wheel and the PKG-INFO file from setuptools render the same way (see pypa/setuptools#4336 for more info)

Closes pypa#395

src/wheel/metadata.py

@@ -139,7 +139,8 @@ def generate_requirements(
             condition = " ; " + condition
 
         for new_req in convert_requirements(depends):
-            yield "Requires-Dist", new_req + condition
+            canonical_req = str(Requirement(new_req + condition))
+            yield "Requires-Dist", canonical_req
 
 
 def pkginfo_to_metadata(egg_info_path: str, pkginfo_path: str) -> Message:

tests/test_metadata.py

@@ -8,26 +8,26 @@ def test_pkginfo_to_metadata(tmp_path):
         ("Metadata-Version", "2.1"),
         ("Name", "spam"),
         ("Version", "0.1"),
-        ("Requires-Dist", "pip @ https://github.com/pypa/pip/archive/1.3.1.zip"),
-        ("Requires-Dist", 'pywin32 ; sys_platform=="win32"'),
-        ("Requires-Dist", 'foo @ http://host/foo.zip ; sys_platform=="win32"'),
+        ("Requires-Dist", "pip@ https://github.com/pypa/pip/archive/1.3.1.zip"),
+        ("Requires-Dist", 'pywin32; sys_platform == "win32"'),
+        ("Requires-Dist", 'foo@ http://host/foo.zip ; sys_platform == "win32"'),
         ("Provides-Extra", "signatures"),
         (
             "Requires-Dist",
-            "pyxdg ; (sys_platform!=\"win32\") and extra == 'signatures'",
+            'pyxdg; sys_platform != "win32" and extra == "signatures"',
         ),
         ("Provides-Extra", "empty_extra"),
         ("Provides-Extra", "extra"),
-        ("Requires-Dist", "bar @ http://host/bar.zip ; extra == 'extra'"),
+        ("Requires-Dist", 'bar@ http://host/bar.zip ; extra == "extra"'),
         ("Provides-Extra", "faster-signatures"),
-        ("Requires-Dist", "ed25519ll ; extra == 'faster-signatures'"),
+        ("Requires-Dist", 'ed25519ll; extra == "faster-signatures"'),
         ("Provides-Extra", "rest"),
-        ("Requires-Dist", "docutils >=0.8 ; extra == 'rest'"),
-        ("Requires-Dist", "keyring ; extra == 'signatures'"),
-        ("Requires-Dist", "keyrings.alt ; extra == 'signatures'"),
+        ("Requires-Dist", 'docutils>=0.8; extra == "rest"'),
+        ("Requires-Dist", 'keyring; extra == "signatures"'),
+        ("Requires-Dist", 'keyrings.alt; extra == "signatures"'),
         ("Provides-Extra", "test"),
-        ("Requires-Dist", "pytest >=3.0.0 ; extra == 'test'"),
-        ("Requires-Dist", "pytest-cov ; extra == 'test'"),
+        ("Requires-Dist", 'pytest>=3.0.0; extra == "test"'),
+        ("Requires-Dist", 'pytest-cov; extra == "test"'),
     ]
 
     pkg_info = tmp_path.joinpath("PKG-INFO")