Correctly handle trailing whitespace on URL requirements

The input is permitted to end, after trailing whitespace.

src/packaging/_parser.py

@@ -89,7 +89,7 @@ def _parse_requirement_details(
     tokenizer: Tokenizer,
 ) -> Tuple[str, str, Optional[MarkerList]]:
     """
-    requirement_details = AT URL (WS requirement_marker)?
+    requirement_details = AT URL (WS requirement_marker?)?
                         | specifier WS? (requirement_marker)?
     """
 
@@ -108,6 +108,10 @@ def _parse_requirement_details(
 
         tokenizer.expect("WS", expected="whitespace after URL")
 
+        # The input might end after whitespace.
+        if tokenizer.check("END", peek=True):
+            return (url, specifier, marker)
+
         marker = _parse_requirement_marker(
             tokenizer, span_start=url_start, after="URL and whitespace"
         )

tests/test_requirements.py

@@ -581,14 +581,14 @@ def test_str_and_repr(
         self, extras: str, url_or_specifier: str, marker: str
     ) -> None:
         # GIVEN
-        to_parse = f"name{extras}{url_or_specifier}{marker}".strip()
+        to_parse = f"name{extras}{url_or_specifier}{marker}"
 
         # WHEN
         req = Requirement(to_parse)
 
         # THEN
-        assert str(req) == to_parse
-        assert repr(req) == f"<Requirement({to_parse!r})>"
+        assert str(req) == to_parse.strip()
+        assert repr(req) == f"<Requirement({to_parse.strip()!r})>"
 
     @pytest.mark.parametrize("dep1, dep2", EQUAL_DEPENDENCIES)
     def test_equal_reqs_equal_hashes(self, dep1: str, dep2: str) -> None: