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Use speculative parsing for with-items (#11770)

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## Summary

This PR updates the with-items parsing logic to use speculative parsing
instead.

### Existing logic

First, let's understand the previous logic:
1. The parser sees `(`, it doesn't know whether it's part of a
parenthesized with items or a parenthesized expression
2. Consider it a parenthesized with items and perform a hand-rolled
speculative parsing
3. Then, verify the assumption and if it's incorrect convert the parsed
with items into an appropriate expression which becomes part of the
first with item

Here, in (3) there are lots of edge cases which we've to deal with:
1. Trailing comma with a single element should be [converted to the
expression as
is](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2140-L2153))
2. Trailing comma with multiple elements should be [converted to a tuple
expression](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2155-L2178))
3. Limit the allowed expression based on whether it's
[(1)](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2144-L2152))
or
[(2)](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2157-L2171))
4. [Consider postfix
expressions](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2181-L2200))
after (3)
5. [Consider `if`
expressions](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2203-L2208))
after (3)
6. [Consider binary
expressions](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2210-L2228))
after (3)

Consider other cases like
* [Single generator
expression](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2020-L2035))
* [Expecting a
comma](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2122-L2130))

And, this is all possible only if we allow parsing these expressions in
the [with item parsing
logic](9b2cf569b2/crates/ruff_python_parser/src/parser/statement.rs (L2287-L2334)).

### Speculative parsing

With #11457 merged, we can simplify this logic by changing the step (3)
from above to just rewind the parser back to the `(` if our assumption
(parenthesized with-items) was incorrect and then continue parsing it
considering parenthesized expression.

This also behaves a lot similar to what a PEG parser does which is to
consider the first grammar rule and if it fails consider the second
grammar rule and so on.

resolves: #11639 

## Test Plan

- [x] Verify the updated snapshots
- [x] Run the fuzzer on around 3000 valid source code (locally)
This commit is contained in:
Dhruv Manilawala 2024-06-06 14:29:56 +05:30 • committed by GitHub
parent 5a5a588a72
commit 6c1fa1d440
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GPG key ID: B5690EEEBB952194
9 changed files with 556 additions and 731 deletions
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61
crates/ruff_python_parser/src/parser/expression.rs
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@ -689,7 +689,8 @@ impl<'src> Parser<'src> {
parsed_expr = Expr::Generator(parser.parse_generator_expression(
parsed_expr.expr,
GeneratorExpressionInParentheses::No(start),
start,
Parenthesized::No,
))
.into();
}
@ -1705,7 +1706,8 @@ impl<'src> Parser<'src> {
let generator = Expr::Generator(self.parse_generator_expression(
parsed_expr.expr,
GeneratorExpressionInParentheses::Yes(start),
start,
Parenthesized::Yes,
));
ParsedExpr {
@ -1929,46 +1931,27 @@ impl<'src> Parser<'src> {
/// Parses a generator expression.
///
/// The given `in_parentheses` parameter is used to determine whether the generator
/// expression is enclosed in parentheses or not:
/// - `Yes`, expect the `)` token after the generator expression.
/// - `No`, no parentheses are expected.
/// - `Maybe`, consume the `)` token if it's present.
///
/// The contained start position in each variant is used to determine the range
/// of the generator expression.
/// The given `start` offset is the start of either the opening parenthesis if the generator is
/// parenthesized or the first token of the expression.
///
/// See: <https://docs.python.org/3/reference/expressions.html#generator-expressions>
pub(super) fn parse_generator_expression(
&mut self,
element: Expr,
in_parentheses: GeneratorExpressionInParentheses,
start: TextSize,
parenthesized: Parenthesized,
) -> ast::ExprGenerator {
let generators = self.parse_generators();
let (parenthesized, start) = match in_parentheses {
GeneratorExpressionInParentheses::Yes(lpar_start) => {
self.expect(TokenKind::Rpar);
(true, lpar_start)
}
GeneratorExpressionInParentheses::No(expr_start) => (false, expr_start),
GeneratorExpressionInParentheses::Maybe {
lpar_start,
expr_start,
} => {
if self.eat(TokenKind::Rpar) {
(true, lpar_start)
} else {
(false, expr_start)
}
}
};
if parenthesized.is_yes() {
self.expect(TokenKind::Rpar);
}
ast::ExprGenerator {
elt: Box::new(element),
generators,
range: self.node_range(start),
parenthesized,
parenthesized: parenthesized.is_yes(),
}
}
@ -2472,26 +2455,6 @@ impl From<Operator> for OperatorPrecedence {
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum GeneratorExpressionInParentheses {
/// The generator expression is in parentheses. The given [`TextSize`] is the
/// start of the left parenthesis. E.g., `(x for x in range(10))`.
Yes(TextSize),
/// The generator expression is not in parentheses. The given [`TextSize`] is the
/// start of the expression. E.g., `x for x in range(10)`.
No(TextSize),
/// The generator expression may or may not be in parentheses. The given [`TextSize`]s
/// are the start of the left parenthesis and the start of the expression, respectively.
Maybe {
/// The start of the left parenthesis.
lpar_start: TextSize,
/// The start of the expression.
expr_start: TextSize,
},
}
/// Represents the precedence used for parsing the value part of a starred expression.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum StarredExpressionPrecedence {