[matthewhughes934]

While working on #7220 I got curious about how the integration tests handle line endings, specifically CRLF, and it turns out they don't. Given we have features that explicitly add/remove these line endings we should ensure the tests correctly cover this case to avoid regressions.

We use diff::lines to generate diffs, and this calls str::lines under the hood, which strip any trailing \r\n or \n. So the only way we can tell that line-endings differ is by comparing the two contents, previously we performed this comparison in a way that would ignore if one file had \r\n endings and another had \n endings. This meant we never actually asserted that we saw the expected line endings.

Note: we can only tell the files have differing line endings, not the lines where this occurs. It could be a future improvement to make this more specific, but I think the approach is reasonable since there aren't any tests (or really any use case) for mixed line-endings in a single file. This reflects the behaviour of how we report such errors with e.g. emitter::diff::DiffEmitter::emit_formatted_file

This required updating some test files that used newline_style=Windows but never actually added those line endings in the corresponding target. In these cases carriage returns are added to the target files, but not the source ones so these tests also assert that we do indeed convert the line endings.

The files
tests/{target,source}/configs/enum_discrim_align_threshold/40.rs had CRLF line endings, but not corresponding newline_style option and the feature does not depend on line endings, so these were converted back to used Unix line endings

• I did not use an LLM to create a change in this PR.
• I used an LLM to create a change in this PR, and I have explained below how it was used.

NB: this diff might not be very helpful to view in the GitHub UI, since it doesn't show line ending changes

[matthewhughes934]

🫠 wrestling with line endings + git is not the most run (git add --renormalize is my friend)

EDIT: why is ./tests/target/empty_file.rs not empty (it contains a newline character)