## Summary
In https://github.com/astral-sh/ruff/pull/6512, we added a flag to the
AST to mark implicitly-concatenated string expressions. This PR makes
use of that flag to remove the `is_implicit_concatenation` method.
## Test Plan
`cargo test`
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## Summary
This PR implements formatting for non-f-string Strings that do not use implicit concatenation.
Docstring formatting is out of the scope of this PR.
<!-- What's the purpose of the change? What does it do, and why? -->
## Test Plan
I added a few tests for simple string literals.
## Performance
Ouch. This is hitting performance somewhat hard. This is probably because we now iterate each string a couple of times:
1. To detect if it is an implicit string continuation
2. To detect if the string contains any new lines
3. To detect the preferred quote
4. To normalize the string
Edit: I integrated the detection of newlines into the preferred quote detection so that we only iterate the string three time.
We can probably do better by merging the implicit string continuation with the quote detection and new line detection by iterating till the end of the string part and returning the offset. We then use our simple tokenizer to skip over any comments or whitespace until we find the first non trivia token. From there we keep continue doing this in a loop until we reach the end o the string. I'll leave this improvement for later.
## Summary
In the rare event that a docstring contains an implicit string concatenation, we currently have the potential to panic, because we assume that if a string starts with triple quotes, it _ends_ with triple quotes. But with implicit concatenation, that's not the case: a single `Expr` could start and end with different quote styles, because it can contain multiple string tokens.
Supporting these "properly" is pretty hard. In some cases it's hard to even know what the "right" behavior is. So for now, I'm just detecting and warning, which is better than a panic.
Closes#3543.
Closes#3585.
# Summary
We need to support CR line endings (as opposed to LF and CRLF line endings, which are already supported). They're rare, but they do appear in Python code, and we tend to panic on any file that uses them.
Our `Locator` abstraction now supports CR line endings. However, Rust's `str#lines` implementation does _not_.
This PR adds a `UniversalNewlineIterator` implementation that respects all of CR, LF, and CRLF line endings, and plugs it into most of the `.lines()` call sites.
As an alternative design, it could be nice if we could leverage `Locator` for this. We've already computed all of the line endings, so we could probably iterate much more efficiently?
# Test Plan
Largely relying on automated testing, however, also ran over some known failure cases, like #3404.
