Normalise Hex and unicode escape sequences in string #9280
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MichaReiser
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MichaReiser
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Dec 26, 2023
| /// * `\u`, `\U'` and `\x`: To use lower case for the characters `a-f`. | ||
| /// * `\N`: To use uppercase letters | ||
| fn normalize(self, input: &str) -> Option<Cow<str>> { | ||
| let mut normalised = String::new(); |
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I tried to avoid the allocation here when the string needs to be normalized, but making it work with the outer normalize_string was somewhat complicated (relative string indices, different iterators etc). That's why I decided to accept the allocation here, considering that we only allocate for non-normalised (unformatted) escape sequences (rare).
There's also the case that we need to be able to recover in case the escape sequence is invalid, which means we can't perform the normalisation in place (and directly push to the outer output String)
MichaReiser
commented
Dec 26, 2023
| fn normalize(self, input: &str) -> Option<Cow<str>> { | ||
| let mut normalised = String::new(); | ||
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| let len = match self { |
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This turned out more complicated than I hoped it would. Maybe a candidate to use a Regex? But I also think it's not worth bothering much. It's relatively straightforward code and I don't expect many changes to it,
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konstin
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Dec 27, 2023
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| _ => { | ||
| // not a valid escape sequence | ||
| return None; | ||
| } |
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Can this happen? I'm getting syntax errors with invalid input (both ruff and cpython)
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Summary
This PR implements Black's
hex_codes_in_unicode_sequencespreview style that normalises escape sequences:\u,\Uin non-byte literals: To use lower-case characters (A-F->a-f)\x: To use lower-case characters (A-F->a-f)\Nin non-byte literals: To use uppercase charactersUsing lowercase characters for hex escape sequences is consistent to Python's
repr.But it has the downside that it is inconsistent with how we (and Black) format numbers in hexadecimal notations:
0xAF.Using lowercase characters is the right choise in my view and I'm leaning towards changing number literals to use lower case too.
But we need to be careful with this because it seems black changed their preference a few times in the past.
Part of #8678
Test Plan
cargo test