[clang] [clang-format] Add KwBreakBeforeCaseLabel (PR #227668)

[Anan Yablonko via cfe-commits]

ananski-the-3rd wrote:


> `Allow` is something I want to get rid of. `CompactCaseLabels` would be okay. How about `CaseLabelsAndPreceedingBreakOnTheSameLine` wordy is not a problem, in my eyes.

I prefer CompactCaseLabels. It's easy to remember and avoids double-meaning of `break`.

> cppfront does not fulfill (even if it had a style guide) the criteria, even a Herb Sutter only counts as one person.

Agreed that cppfront doesn't quite meet the bar.

> A simple `[[fallthrough]]` does better stand out. On that matter, how should that look like with the proposed option?

I come from C, so I hadn't considered this attribute. As a reader of C++ I'd prefer:
```cpp
switch (*c) {
  break; case 'a':
    foo();
  [[fallthrough]]; case 'b':
    bar();
  break; default:
    baz();
}
```
That isn't implemented yet. Currently it formats as:
```cpp
switch (*c) {
  break; case 'a':
    foo();
    [[fallthrough]];  // or a fallthrough comment in C
  case 'b':
    bar();
  break; default:
    baz();
}
```
Which is also readable in my eyes. I can add the first version if you'd like.

> The current proposal comes into a range, where I could accept it, while I currently can't guarantee a merge, working on it is also not definitely wasted time.

I hope so.

Thanks,
Anan


https://github.com/llvm/llvm-project/pull/227668