[clang-format] Continuation indent of requires-expression should be configurable

[Vigilans]

In clang-13, a concept definition with requires-expression will be formatted like this:

template <typename EnvT>
concept Env = requires(EnvT&& env) {
    { step(env) } -> std::convertible_to<int>;
};

But after commits in https://reviews.llvm.org/D113319, above code will be formatted to:

template <typename EnvT>
concept Env = requires (EnvT&& env) {
                  { step(env) } -> std::convertible_to<int>;
              };

After some investigation, it reveals that the difference was rooted in following code:

llvm-project/clang/lib/Format/ContinuationIndenter.cpp

Lines 1399 to 1400 in 24d6cc6

	if (Current.is(TT_RequiresExpression))
	CurrentState.NestedBlockIndent = State.Column;

It unconditionally sets the indentation to be aligned with requires keyword. After removing it and recompile clang-format, the code is formatted as what clang-13 does:

template <typename EnvT>
concept Env = requires (EnvT&& env) {
    { step(env) } -> std::convertible_to<int>;
};

These two indentations are just different style preferences, therefore should be made configurable in .clang-format file.

@HazardyKnusperkeks

[llvmbot]

@llvm/issue-subscribers-clang-format

[llvmbot]

@llvm/issue-subscribers-good-first-issue

[HazardyKnusperkeks]

You are very welcome to add an option, I'll gladly review it. But my own time is very limited to work on this.

[eoan-ermine]

I'll work on it

[eoan-ermine]

Phabricator https://reviews.llvm.org/D129443

[rymiel]

I think this issue is assigned to the wrong person?

Also, the patch seems very close to the finish line, seems like it only has a few remaining nits? (If the original author can't, can someone (e.g me) give it the final push?)

[owenca]

@rymiel go ahead and re-assign it to yourself and commandeer the patch.