Greatly speed up nested array parsing#702
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GuillaumeGomez merged 5 commits intoaskama-rs:mainfrom Feb 17, 2026
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Kijewski
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Feb 16, 2026
askama_parser/src/expr.rs
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695
| if elements.is_empty() { | ||
| return cut_error!( | ||
| "expected element expression for array repeat syntax", | ||
| sub_span | ||
| ); | ||
| } else if elements.len() != 1 { | ||
| return cut_error!( | ||
| "unexpected `;` after expression", | ||
| elements.last().unwrap().span() | ||
| ); | ||
| } | ||
| let count = terminated(Self::array_repeat_count, ']').parse_next(i)?; | ||
| return Ok(WithSpan::new( | ||
| Box::new(Self::ArrayRepeat(elements.pop().unwrap(), count)), |
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let Some(elem) = elements.pop() else {
"expected element expression for array repeat syntax"
};
if !elements.is_empty() {
"unexpected `;` after expression"
}
return Ok();
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It's nicer, good idea!
Kijewski
reviewed
Feb 16, 2026
askama_parser/src/expr.rs
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Comment on lines
681
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691
| if ws(';').parse_next(i).is_ok() { | ||
| if elements.is_empty() { | ||
| return cut_error!( | ||
| "expected element expression for array repeat syntax", | ||
| sub_span | ||
| ); | ||
| } else if elements.len() != 1 { | ||
| return cut_error!( | ||
| "unexpected `;` after expression", | ||
| elements.last().unwrap().span() | ||
| ); |
Member
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if let Some(span) = opt(ws(';')).span().parse_next(i)? {
if .. {
return cut_error!("unexpected `;` after expression", span);
}
}
Member
|
Oh, that's much nicer than potentially parsing everything twice! Just two minor comments. |
Collaborator
Author
|
Applied comments. :) |
* inline tiny function `array_repeat_element` * make sure to return an error with a message * for errors with array repeat, point to the `;`, not `[` * re-use `any_rust_token()` to tell what we found instead of `]` * add grouping characters to `any_rust_token()`
Member
|
I was not happy with the uninformative "failed to parse template source" error messages, so I tried to better derive the error condition and position. |
Collaborator
Author
|
Can't approve your commit but it's a great improvement, thanks! |
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Fixes https://oss-fuzz.com/testcase-detail/5640096178307072.
The problem was that, we went into the two full array parsing branches and if any failed, we tried the other one, and if this failed, we returned and then we repeat. It's fine as long as the error isn't super deep nested.
This fix simply gets all repeated exprs, and then check if a
;is next and then handle errors if any. So we have only one path instead of 2. And as a nice bonus, code is shorter. :)