Improve parser error messaging around mistakes in/around version specifiers

src/packaging/_parser.py

@@ -163,7 +163,11 @@ def _parse_extras(tokenizer: Tokenizer) -> List[str]:
     if not tokenizer.check("LEFT_BRACKET", peek=True):
         return []
 
-    with tokenizer.enclosing_tokens("LEFT_BRACKET", "RIGHT_BRACKET"):
+    with tokenizer.enclosing_tokens(
+        "LEFT_BRACKET",
+        "RIGHT_BRACKET",
+        around="extras",
+    ):
         tokenizer.consume("WS")
         extras = _parse_extras_list(tokenizer)
         tokenizer.consume("WS")
@@ -203,7 +207,11 @@ def _parse_specifier(tokenizer: Tokenizer) -> str:
     specifier = LEFT_PARENTHESIS WS? version_many WS? RIGHT_PARENTHESIS
               | WS? version_many WS?
     """
-    with tokenizer.enclosing_tokens("LEFT_PARENTHESIS", "RIGHT_PARENTHESIS"):
+    with tokenizer.enclosing_tokens(
+        "LEFT_PARENTHESIS",
+        "RIGHT_PARENTHESIS",
+        around="version specifier",
+    ):
         tokenizer.consume("WS")
         parsed_specifiers = _parse_version_many(tokenizer)
         tokenizer.consume("WS")
@@ -217,7 +225,14 @@ def _parse_version_many(tokenizer: Tokenizer) -> str:
     """
     parsed_specifiers = ""
     while tokenizer.check("SPECIFIER"):
+        span_start = tokenizer.position
         parsed_specifiers += tokenizer.read().text
+        if tokenizer.check("VERSION_PREFIX_TRAIL", peek=True):
+            tokenizer.raise_syntax_error(
+                ".* suffix can only be used with `==` or `!=` operators",
+                span_start=span_start,
+                span_end=tokenizer.position + 1,
+            )
         tokenizer.consume("WS")
         if not tokenizer.check("COMMA"):
             break
@@ -254,7 +269,11 @@ def _parse_marker_atom(tokenizer: Tokenizer) -> MarkerAtom:
 
     tokenizer.consume("WS")
     if tokenizer.check("LEFT_PARENTHESIS", peek=True):
-        with tokenizer.enclosing_tokens("LEFT_PARENTHESIS", "RIGHT_PARENTHESIS"):
+        with tokenizer.enclosing_tokens(
+            "LEFT_PARENTHESIS",
+            "RIGHT_PARENTHESIS",
+            around="marker expression",
+        ):
             tokenizer.consume("WS")
             marker: MarkerAtom = _parse_marker(tokenizer)
             tokenizer.consume("WS")

src/packaging/_tokenizer.py

@@ -78,6 +78,7 @@ def __str__(self) -> str:
     "AT": r"\@",
     "URL": r"[^ \t]+",
     "IDENTIFIER": r"\b[a-zA-Z0-9][a-zA-Z0-9._-]*\b",
+    "VERSION_PREFIX_TRAIL": r"\.\*",
     "WS": r"[ \t]+",
     "END": r"$",
 }
@@ -167,21 +168,23 @@ def raise_syntax_error(
         )
 
     @contextlib.contextmanager
-    def enclosing_tokens(self, open_token: str, close_token: str) -> Iterator[bool]:
+    def enclosing_tokens(
+        self, open_token: str, close_token: str, *, around: str
+    ) -> Iterator[None]:
         if self.check(open_token):
             open_position = self.position
             self.read()
         else:
             open_position = None
 
-        yield open_position is not None
+        yield
 
         if open_position is None:
             return
 
         if not self.check(close_token):
             self.raise_syntax_error(
-                f"Expected closing {close_token}",
+                f"Expected matching {close_token} for {open_token}, after {around}",
                 span_start=open_position,
             )
 

tests/test_requirements.py

@@ -279,11 +279,28 @@ def test_error_when_parens_not_closed_correctly(self) -> None:
         # THEN
         assert ctx.exconly() == (
             "packaging.requirements.InvalidRequirement: "
-            "Expected closing RIGHT_PARENTHESIS\n"
+            "Expected matching RIGHT_PARENTHESIS for LEFT_PARENTHESIS, "
+            "after version specifier\n"
             "    name (>= 1.0\n"
             "         ~~~~~~~^"
         )
 
+    def test_error_when_prefix_match_is_used_incorrectly(self) -> None:
+        # GIVEN
+        to_parse = "black (>=20.*) ; extra == 'format'"
+
+        # WHEN
+        with pytest.raises(InvalidRequirement) as ctx:
+            Requirement(to_parse)
+
+        # THEN
+        assert ctx.exconly() == (
+            "packaging.requirements.InvalidRequirement: "
+            ".* suffix can only be used with `==` or `!=` operators\n"
+            "    black (>=20.*) ; extra == 'format'\n"
+            "           ~~~~~^"
+        )
+
     def test_error_when_bracket_not_closed_correctly(self) -> None:
         # GIVEN
         to_parse = "name[bar, baz >= 1.0"
@@ -295,7 +312,8 @@ def test_error_when_bracket_not_closed_correctly(self) -> None:
         # THEN
         assert ctx.exconly() == (
             "packaging.requirements.InvalidRequirement: "
-            "Expected closing RIGHT_BRACKET\n"
+            "Expected matching RIGHT_BRACKET for LEFT_BRACKET, "
+            "after extras\n"
             "    name[bar, baz >= 1.0\n"
             "        ~~~~~~~~~~^"
         )
@@ -311,7 +329,8 @@ def test_error_when_extras_bracket_left_unclosed(self) -> None:
         # THEN
         assert ctx.exconly() == (
             "packaging.requirements.InvalidRequirement: "
-            "Expected closing RIGHT_BRACKET\n"
+            "Expected matching RIGHT_BRACKET for LEFT_BRACKET, "
+            "after extras\n"
             "    name[bar, baz\n"
             "        ~~~~~~~~~^"
         )
@@ -332,6 +351,23 @@ def test_error_no_space_after_url(self) -> None:
             "           ~~~~~~~~~~~~~~~~~~~~~~^"
         )
 
+    def test_error_marker_bracket_unclosed(self) -> None:
+        # GIVEN
+        to_parse = "name; (extra == 'example'"
+
+        # WHEN
+        with pytest.raises(InvalidRequirement) as ctx:
+            Requirement(to_parse)
+
+        # THEN
+        assert ctx.exconly() == (
+            "packaging.requirements.InvalidRequirement: "
+            "Expected matching RIGHT_PARENTHESIS for LEFT_PARENTHESIS, "
+            "after marker expression\n"
+            "    name; (extra == 'example'\n"
+            "          ~~~~~~~~~~~~~~~~~~~^"
+        )
+
     def test_error_no_url_after_at(self) -> None:
         # GIVEN
         to_parse = "name @ "