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[syntax-errors] Named expressions in decorators before Python 3.9 (#16386)
Summary -- This PR detects the relaxed grammar for decorators proposed in [PEP 614](https://peps.python.org/pep-0614/) on Python 3.8 and lower. The 3.8 grammar for decorators is [here](https://docs.python.org/3.8/reference/compound_stmts.html#grammar-token-decorators): ``` decorators ::= decorator+ decorator ::= "@" dotted_name ["(" [argument_list [","]] ")"] NEWLINE dotted_name ::= identifier ("." identifier)* ``` in contrast to the current grammar [here](https://docs.python.org/3/reference/compound_stmts.html#grammar-token-python-grammar-decorators) ``` decorators ::= decorator+ decorator ::= "@" assignment_expression NEWLINE assignment_expression ::= [identifier ":="] expression ``` Test Plan -- New inline parser tests.
1 parent d062388 commit 318f503

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‎crates/ruff_python_parser/resources/inline/err/decorator_expression_py38.py

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# parse_options: { "target-version": "3.8" }
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@buttons[0].clicked.connect
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def spam(): ...

‎crates/ruff_python_parser/resources/inline/err/decorator_named_expression_py37.py

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# parse_options: { "target-version": "3.7" }
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@(x := lambda x: x)(foo)
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def bar(): ...

‎crates/ruff_python_parser/resources/inline/ok/decorator_expression_dotted_ident_py38.py

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# parse_options: { "target-version": "3.8" }
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@buttons.clicked.connect
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def spam(): ...

‎crates/ruff_python_parser/resources/inline/ok/decorator_expression_eval_hack_py38.py

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# parse_options: { "target-version": "3.8" }
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@eval("buttons[0].clicked.connect")
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def spam(): ...

‎crates/ruff_python_parser/resources/inline/ok/decorator_expression_identity_hack_py38.py

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# parse_options: { "target-version": "3.8" }
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def _(x): return x
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@_(buttons[0].clicked.connect)
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def spam(): ...

‎crates/ruff_python_parser/resources/inline/ok/decorator_expression_py39.py

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# parse_options: { "target-version": "3.9" }
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@buttons[0].clicked.connect
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def spam(): ...
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@(x := lambda x: x)(foo)
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def bar(): ...

‎crates/ruff_python_parser/src/error.rs

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@@ -449,6 +449,37 @@ pub enum UnsupportedSyntaxErrorKind {
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Match,
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Walrus,
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ExceptStar,
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/// Represents the use of a "relaxed" [PEP 614] decorator before Python 3.9.
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///
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/// ## Examples
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///
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/// Prior to Python 3.9, decorators were defined to be [`dotted_name`]s, optionally followed by
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/// an argument list. For example:
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///
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/// ```python
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/// @buttons.clicked.connect
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/// def foo(): ...
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///
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/// @buttons.clicked.connect(1, 2, 3)
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/// def foo(): ...
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/// ```
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///
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/// As pointed out in the PEP, this prevented reasonable extensions like subscripts:
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///
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/// ```python
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/// buttons = [QPushButton(f'Button {i}') for i in range(10)]
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///
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/// @buttons[0].clicked.connect
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/// def spam(): ...
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/// ```
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///
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/// Python 3.9 removed these restrictions and expanded the [decorator grammar] to include any
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/// assignment expression and include cases like the example above.
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///
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/// [PEP 614]: https://peps.python.org/pep-0614/
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/// [`dotted_name`]: https://docs.python.org/3.8/reference/compound_stmts.html#grammar-token-dotted-name
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/// [decorator grammar]: https://docs.python.org/3/reference/compound_stmts.html#grammar-token-python-grammar-decorator
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RelaxedDecorator,
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/// Represents the use of a [PEP 570] positional-only parameter before Python 3.8.
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///
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/// ## Examples
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UnsupportedSyntaxErrorKind::Match => "Cannot use `match` statement",
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UnsupportedSyntaxErrorKind::Walrus => "Cannot use named assignment expression (`:=`)",
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UnsupportedSyntaxErrorKind::ExceptStar => "Cannot use `except*`",
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UnsupportedSyntaxErrorKind::RelaxedDecorator => "Unsupported expression in decorators",
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UnsupportedSyntaxErrorKind::PositionalOnlyParameter => {
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"Cannot use positional-only parameter separator"
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}
@@ -538,6 +570,7 @@ impl UnsupportedSyntaxErrorKind {
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UnsupportedSyntaxErrorKind::Match => PythonVersion::PY310,
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UnsupportedSyntaxErrorKind::Walrus => PythonVersion::PY38,
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UnsupportedSyntaxErrorKind::ExceptStar => PythonVersion::PY311,
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UnsupportedSyntaxErrorKind::RelaxedDecorator => PythonVersion::PY39,
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UnsupportedSyntaxErrorKind::PositionalOnlyParameter => PythonVersion::PY38,
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UnsupportedSyntaxErrorKind::TypeParameterList => PythonVersion::PY312,
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UnsupportedSyntaxErrorKind::TypeAliasStatement => PythonVersion::PY312,

‎crates/ruff_python_parser/src/parser/expression.rs

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@@ -632,7 +632,7 @@ impl<'src> Parser<'src> {
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/// If the parser isn't position at a `(` token.
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///
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/// See: <https://docs.python.org/3/reference/expressions.html#calls>
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fn parse_call_expression(&mut self, func: Expr, start: TextSize) -> ast::ExprCall {
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pub(super) fn parse_call_expression(&mut self, func: Expr, start: TextSize) -> ast::ExprCall {
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let arguments = self.parse_arguments();
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ast::ExprCall {

‎crates/ruff_python_parser/src/parser/helpers.rs

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@@ -43,3 +43,15 @@ pub(super) const fn token_kind_to_cmp_op(tokens: [TokenKind; 2]) -> Option<CmpOp
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_ => return None,
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})
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}
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/// Helper for `parse_decorators` to determine if `expr` is a [`dotted_name`] from the decorator
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/// grammar before Python 3.9.
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///
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/// [`dotted_name`]: https://docs.python.org/3.8/reference/compound_stmts.html#grammar-token-dotted-name
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pub(super) fn is_name_or_attribute_expression(expr: &Expr) -> bool {
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match expr {
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Expr::Attribute(attr) => is_name_or_attribute_expression(&attr.value),
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Expr::Name(_) => true,
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_ => false,
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}
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}

‎crates/ruff_python_parser/src/parser/statement.rs

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@@ -5,7 +5,8 @@ use rustc_hash::{FxBuildHasher, FxHashSet};
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use ruff_python_ast::name::Name;
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use ruff_python_ast::{
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self as ast, ExceptHandler, Expr, ExprContext, IpyEscapeKind, Operator, Stmt, WithItem,
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self as ast, ExceptHandler, Expr, ExprContext, IpyEscapeKind, Operator, PythonVersion, Stmt,
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WithItem,
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};
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use ruff_text_size::{Ranged, TextRange, TextSize};
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@@ -2599,14 +2600,63 @@ impl<'src> Parser<'src> {
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let decorator_start = self.node_start();
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self.bump(TokenKind::At);
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let parsed_expr = self.parse_named_expression_or_higher(ExpressionContext::default());
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if self.options.target_version < PythonVersion::PY39 {
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// test_ok decorator_expression_dotted_ident_py38
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// # parse_options: { "target-version": "3.8" }
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// @buttons.clicked.connect
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// def spam(): ...
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// test_ok decorator_expression_identity_hack_py38
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// # parse_options: { "target-version": "3.8" }
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// def _(x): return x
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// @_(buttons[0].clicked.connect)
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// def spam(): ...
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// test_ok decorator_expression_eval_hack_py38
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// # parse_options: { "target-version": "3.8" }
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// @eval("buttons[0].clicked.connect")
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// def spam(): ...
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// test_ok decorator_expression_py39
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// # parse_options: { "target-version": "3.9" }
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// @buttons[0].clicked.connect
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// def spam(): ...
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// @(x := lambda x: x)(foo)
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// def bar(): ...
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// test_err decorator_expression_py38
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// # parse_options: { "target-version": "3.8" }
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// @buttons[0].clicked.connect
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// def spam(): ...
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// test_err decorator_named_expression_py37
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// # parse_options: { "target-version": "3.7" }
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// @(x := lambda x: x)(foo)
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// def bar(): ...
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let allowed_decorator = match &parsed_expr.expr {
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Expr::Call(expr_call) => {
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helpers::is_name_or_attribute_expression(&expr_call.func)
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}
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expr => helpers::is_name_or_attribute_expression(expr),
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};
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if !allowed_decorator {
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self.add_unsupported_syntax_error(
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UnsupportedSyntaxErrorKind::RelaxedDecorator,
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parsed_expr.range(),
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);
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}
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}
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// test_err decorator_invalid_expression
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// @*x
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// @(*x)
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// @((*x))
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// @yield x
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// @yield from x
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// def foo(): ...
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let parsed_expr = self.parse_named_expression_or_higher(ExpressionContext::default());
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decorators.push(ast::Decorator {
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expression: parsed_expr.expr,

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