[syntax-errors] Fix star annotation before Python 3.11 (#16878)

ntBre · web-flow · commit 42cbce538b57 · 2025-03-20T17:44:52.000-04:00
Summary -- Fixes #16874. I previously emitted a syntax error when starred annotations were _allowed_ rather than when they were actually used. This caused false positives for any starred parameter name because these are allowed to have starred annotations but not required to. The fix is to check if the annotation is actually starred after parsing it. Test Plan -- New inline parser tests derived from the initial report and more examples from the comments, although I think the first case should cover them all.
diff --git a/crates/ruff_python_parser/resources/inline/ok/param_with_star_annotation_py310.py b/crates/ruff_python_parser/resources/inline/ok/param_with_star_annotation_py310.py
@@ -0,0 +1,9 @@
+# parse_options: {"target-version": "3.10"}
+# regression tests for https://github.com/astral-sh/ruff/issues/16874
+# starred parameters are fine, just not the annotation
+from typing import Annotated, Literal
+def foo(*args: Ts): ...
+def foo(*x: Literal["this should allow arbitrary strings"]): ...
+def foo(*x: Annotated[str, "this should allow arbitrary strings"]): ...
+def foo(*args: str, **kwds: int): ...
+def union(*x: A | B): ...
diff --git a/crates/ruff_python_parser/src/parser/statement.rs b/crates/ruff_python_parser/src/parser/statement.rs
@@ -2959,13 +2959,26 @@ impl<'src> Parser<'src> {
                             // # parse_options: {"target-version": "3.11"}
                             // def foo(*args: *Ts): ...
 
+                            // test_ok param_with_star_annotation_py310
+                            // # parse_options: {"target-version": "3.10"}
+                            // # regression tests for https://github.com/astral-sh/ruff/issues/16874
+                            // # starred parameters are fine, just not the annotation
+                            // from typing import Annotated, Literal
+                            // def foo(*args: Ts): ...
+                            // def foo(*x: Literal["this should allow arbitrary strings"]): ...
+                            // def foo(*x: Annotated[str, "this should allow arbitrary strings"]): ...
+                            // def foo(*args: str, **kwds: int): ...
+                            // def union(*x: A | B): ...
+
                             // test_err param_with_star_annotation_py310
                             // # parse_options: {"target-version": "3.10"}
                             // def foo(*args: *Ts): ...
-                            self.add_unsupported_syntax_error(
-                                UnsupportedSyntaxErrorKind::StarAnnotation,
-                                parsed_expr.range(),
-                            );
+                            if parsed_expr.is_starred_expr() {
+                                self.add_unsupported_syntax_error(
+                                    UnsupportedSyntaxErrorKind::StarAnnotation,
+                                    parsed_expr.range(),
+                                );
+                            }
 
                             parsed_expr
                         }
diff --git a/crates/ruff_python_parser/tests/snapshots/valid_syntax@param_with_star_annotation_py310.py.snap b/crates/ruff_python_parser/tests/snapshots/valid_syntax@param_with_star_annotation_py310.py.snap
