[clangd-dev] textDocument/onTypeFormatting and live indentation.

Alex L via clangd-dev clangd-dev at lists.llvm.org
Fri Sep 7 12:56:02 PDT 2018

Thanks for the detailed responses!
I definitely agree that Clangd should provide more than just indentation.
Your examples perfectly illustrate what kind of live formatting should be

On Fri, 7 Sep 2018 at 06:25, Sam McCall <sammccall at google.com> wrote:

> We've had some discussion in the past about the right way for clang-format
> to support live-formatting cases.
> IIRC clang-format doesn't have any current logic specific to this, instead
> having "format these ranges". That mode works well for formatting only
> changed lines and similar cases, but it may or may not be the right model
> for format-as-you-type.

Right. After some experiments I started leaning towards it being not the
right model. Ideally we'd have something better, just like you describe

> In particular I don't think this model will ever give you useful
> autoindent, because if you were *checking in the code* instead of
> continuing to type, you'd want the leading spaces gone.
> So we'd probably need to either:
>  - add a new "as-you-type" mode or entrypoint in clang-format's core, and
> carefully decide what new features it needs and how they should interact
> with clang-format's existing model, or
>  - hack something together outside of clang-format's core (possibly
> reusing its parser)

One other hand-wavy solution that I considered: insert a fake cursor token
into the token stream which will be have the effect of reindenting the line
correctly, e.g.

1. Reformatting braces.
if (foo) {^}

if (foo) {
  ^ // clang-format will treat the cursor as a special token, and thus
won't format the 'if' as if its body was empty.

> My sense is that the first is likely to give better results, e.g. in the
> reformatting braces cases the cursor/indentation and braces may interact.
Either way it might make sense to provide the result as a clang-format API,
> rather than building the logic inside clangd directly.


Better live formatting is definitely something that we need down the line,
but I'm not planning to work on it as of yet. I'll keep this on my list of
potential things to do in Clangd for now, but I won't mind if someone else
picks it up. I'll update the list if I'll have more
ideas/thoughts/proposals for this problem.


> On Thu, Sep 6, 2018 at 8:27 PM Alex L via clangd-dev <
> clangd-dev at lists.llvm.org> wrote:
>> Hi,
>> I would like to implement clang-format aware newline indentation in
>> Clangd. It looks like Clangd only supports '}' trigger character for the
>> 'onTypeFormatting' request. Would it make sense to extend it to support the
>> newline character, and to insert appropriate indentation instead of
>> reformatting the range in that case?
>> Cheers,
>> Alex
>> _______________________________________________
>> clangd-dev mailing list
>> clangd-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/clangd-dev
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