Relax PEP 508 url validation.

packaging/requirements.py

@@ -111,9 +111,7 @@ def __init__(self, requirement_string: str) -> None:
             if parsed_url.scheme == "file":
                 if urllib.parse.urlunparse(parsed_url) != req.url:
                     raise InvalidRequirement("Invalid URL given")
-            elif not (parsed_url.scheme and parsed_url.netloc) or (
-                not parsed_url.scheme and not parsed_url.netloc
-            ):
+            elif not parsed_url.scheme:
                 raise InvalidRequirement(f"Invalid URL: {req.url}")
             self.url: TOptional[str] = req.url
         else:

tests/test_requirements.py

@@ -100,11 +100,14 @@ def test_url_and_marker(self):
         assert parsed.url == "http://example.com"
         assert str(parsed.marker) == 'os_name == "a"'
 
-    def test_invalid_url(self):
+    @pytest.mark.parametrize(
+        "invalid_url", ["/foo/bar", "/foo", "./foo/bar", "./foo", "foo"]
+    )
+    def test_invalid_url(self, invalid_url):
         with pytest.raises(InvalidRequirement) as e:
-            Requirement("name @ gopher:/foo/com")
+            Requirement("name @ " + invalid_url)
         assert "Invalid URL: " in str(e.value)
-        assert "gopher:/foo/com" in str(e.value)
+        assert invalid_url in str(e.value)
 
     def test_file_url(self):
         req = Requirement("name @ file:///absolute/path")
@@ -118,6 +121,19 @@ def test_invalid_file_urls(self):
         with pytest.raises(InvalidRequirement):
             Requirement("name @ file:/.")
 
+    def test_vcs_url(self):
+        req = Requirement("name @ git+https://g.c/u/r.git")
+        self._assert_requirement(req, "name", "git+https://g.c/u/r.git")
+        req = Requirement("name @ git+file:///data/repo")
+        self._assert_requirement(req, "name", "git+file:///data/repo")
+
+    @pytest.mark.parametrize(
+        "url", ["gopher:/foo/com", "mailto:me@example.com", "c:/foo/bar"]
+    )
+    def test_exotic_urls(self, url):
+        req = Requirement("name @ " + url)
+        self._assert_requirement(req, "name", url)
+
     def test_extras_and_url_and_marker(self):
         req = Requirement("name [fred,bar] @ http://foo.com ; python_version=='2.7'")
         self._assert_requirement(