[cfe-dev] Extending clang-format

[Daniel Jasper via cfe-dev]

First off, please read:
http://clang.llvm.org/docs/ClangFormatStyleOptions.html#adding-additional-style-options

My initial thoughts on the two requested changes:

Namespaces: This isn't worth adding the complexity for. Yes, it wastes a
bit of vertical space, but it is also in a place in the file where vertical
space really doesn't matter this much. Plus, with C++17, this is going to
become a non-issue as you can just declare "namespace a::b::c {". I feel
like there has been an argument about this before.

Function parameters: This goes against some quite fundamental assumptions,
that clang-format is making. While it certainly can be done, I'd be
hesitant to get this in unless there is strong evidence that the
requirements presented in the link are fulfilled.

Sorry, I actually hate being so negative. However, I also want clang-format
to remain maintainable and provide the best possible experience for most
people.

Cheers,
Daniel


On Fri, Oct 30, 2015 at 6:23 PM, Andrew Hankins via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi all,
>
> First post.
>
> I've found clang-format to be a very powerful and useful tool and I'd like
> to start extending it to support some other formatting styles that I have
> to work with. The two changes I'd like to start with are to namespaces and
> function parameters.
> For namespaces I'd like create a configuration parameter that would allow
> nested namespaces all on one line.
>
> Rather than
>
> namespace a {
> namespace b {
> namespace c{
> }
> }
> };
>
> Support
>
> namespace a { namespace b { namespace c {
> }}};
>
> and for functions rather than
>
> int foo(int param1,
>           int param2)
> {
> }
>
> Support
>
> int foo
> (
>     int param1,
>     int pararm2
> )
> {
> }
>
>
> I've started to poke around in the clang lib/Format code but I'm finding
> it difficult to figure out where the best place to make the changes is and
> there isn't much documentation on the clang-format design/code I can find.
> I think the rough idea in clang-format is to use the UnwrappedLineParser
> to separate the code into the appropriate lines, then using the
> UnwrappedLineFormatter annotate the tokens, merge lines where possible and
> delete unnecessary lines then finally dump it all.
>
> Taking my namespace change for example I've made modifications to the
> UnwrappedLineParser::parseBlock so it won't always add a newline from
> parseNamespace
>
> -----------------------------------------------------
> @@ -399,7 +399,7 @@ void UnwrappedLineParser::calculateBraceTypes(bool
> ExpectClassBody) {
>  }
>
>  void UnwrappedLineParser::parseBlock(bool MustBeDeclaration, bool
> AddLevel,
> -                                     bool MunchSemi) {
> +                                     bool MunchSemi, bool AddLine) {
>    assert(FormatTok->isOneOf(tok::l_brace, TT_MacroBlockBegin) &&
>           "'{' or macro block token expected");
>    const bool MacroBlock = FormatTok->is(TT_MacroBlockBegin);
> @@ -410,7 +410,7 @@ void UnwrappedLineParser::parseBlock(bool
> MustBeDeclaration, bool AddLevel,
>    if (MacroBlock && FormatTok->is(tok::l_paren))
>      parseParens();
>
> -  addUnwrappedLine();
> +  if (AddLine) addUnwrappedLine();
>
>    ScopedDeclarationState DeclarationState(*Line, DeclarationScopeStack,
>                                            MustBeDeclaration);
> ---------------------------------
>
> and this works somewhat but the namespaces are now missing whitespaces and
> you get
>
> namespace a{namespace b{namespace c{
> }
> }
> }
>
> So instead should I write a line merger for namespaces? Or should I find a
> way to update the insert whitespace before/after flag?
>
> I guess I'm just looking for some guidance on how to best approach this
> kind of work or to be pointed in the direction of more doco.
>
> Thanks in advance,
>
> Andrew
>
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> cfe-dev at lists.llvm.org
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>
>
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