parse_marker should consume the entire source string

Author: mwerschy

src/packaging/_parser.py

@@ -252,7 +252,13 @@ def _parse_version_many(tokenizer: Tokenizer) -> str:
 # Recursive descent parser for marker expression
 # --------------------------------------------------------------------------------------
 def parse_marker(source: str) -> MarkerList:
-    return _parse_marker(Tokenizer(source, rules=DEFAULT_RULES))
+    return _parse_marker_start(Tokenizer(source, rules=DEFAULT_RULES))
+
+
+def _parse_marker_start(tokenizer: Tokenizer) -> MarkerList:
+    expression = _parse_marker(tokenizer)
+    tokenizer.expect("END", expected="end of marker")
+    return expression
 
 
 def _parse_marker(tokenizer: Tokenizer) -> MarkerList: