Improve error shown when there's no space between semicolon and url

packaging/_parser.py

@@ -77,18 +77,27 @@ def parse_named_requirement(requirement: str) -> Requirement:
         url = tokens.read().text[1:].strip()
     elif not tokens.match("END"):
         specifier = parse_specifier(tokens)
+    marker = ""
     if tokens.try_read("SEMICOLON"):
-        marker = ""
         while not tokens.match("END"):
             # we don't validate markers here, it's done later as part of
             # packaging/requirements.py
             marker += tokens.read().text
-    else:
-        marker = ""
-        tokens.expect(
-            "END",
-            error_message="Expected semicolon (followed by markers) or end of string",
-        )
+    elif not tokens.match("END"):
+        if url and url[-1] == ";":
+            error_msg = (
+                "Expected space before semicolon (followed by markers) or end of string"
+            )
+            # update position to point at the place where the space was expected
+            tokens.position -= 1
+            suffix = (
+                f"Maybe you mean this instead?\n    "
+                f"{tokens.source[:tokens.position]} {tokens.source[tokens.position:]}"
+            )
+        else:
+            error_msg = "Expected semicolon (followed by markers) or end of string"
+            suffix = ""
+        tokens.raise_syntax_error(message=error_msg, suffix=suffix)
     return Requirement(name, url, extras, specifier, marker)
 
 

packaging/_tokenizer.py

@@ -129,16 +129,16 @@ def try_read(self, *name: str) -> Optional[Token]:
             return self.read()
         return None
 
-    def raise_syntax_error(self, *, message: str) -> NoReturn:
+    def raise_syntax_error(self, *, message: str, suffix: str = "") -> NoReturn:
         """
         Raise SyntaxError at the given position in the marker.
         """
         at = f"at position {self.position}:"
         marker = " " * self.position + "^"
-        raise ParseExceptionError(
-            f"{message}\n{at}\n    {self.source}\n    {marker}",
-            self.position,
-        )
+        message = f"{message}\n{at}\n    {self.source}\n    {marker}"
+        if suffix:
+            message = f"{message}\n{suffix}"
+        raise ParseExceptionError(message, self.position)
 
     def _make_token(self, name: str, text: str) -> Token:
         """

tests/test_requirements.py

@@ -196,6 +196,14 @@ def test_marker_with_missing_semicolon(self):
             Requirement('name[bar]>=3 python_version == "2.7"')
         assert "Expected semicolon (followed by markers) or end of string" in str(e)
 
+    def test_url_and_marker_with_missing_space_after_semicolon(self):
+        with pytest.raises(InvalidRequirement) as e:
+            Requirement('foobar @ https://foo.com; python_version < "3.11"')
+        assert (
+            "Expected space before semicolon (followed by markers) or end of string"
+            in str(e)
+        )
+
     def test_types(self):
         req = Requirement("foobar[quux]<2,>=3; os_name=='a'")
         assert isinstance(req.name, str)