[cfe-dev] RFC: Extend clang-format to support more/all C-like languages

[Daniel Jasper]

The context-free parser implemented in clang-format is capable of (or can
easily be extended to) understand the structure of basically all C-like
languages. A basic definition of C-like languages is the “Influenced”
section of C’s Wikipedia page [1].

At most, this includes: AMPL, AWK, csh, C++, C--, C#, Objective-C, BitC, D,
Go, Rust, Java, JavaScript, Limbo, LPC, Perl, PHP, Pike, Processing, Seed7,
Verilog. Today, clang-format already supports C, C++, Objective-C and
Objective-C++. Starting from there, it seems almost trivial to extend
support to JavaScript and Java which only contain a small number of
additional syntactical constructs and can be tokenized with Clang’s lexer.
Eventually, we also imagine (and would love to see patches for) formatting
C#, D, Go, Rust, and PHP based on their similar syntax and active usage.
Maybe there are others the community would be interested in seeing?

The benefit of using the same format tool for all these jobs is that many
of clang-format’s advanced formatting algorithms (e.g. Tex-like analysis of
the entire solution space) are immediately available to the other languages.

Concrete proposal:

Start with JavaScript. Syntactically, it is very close to C++ and there are
already different efforts going on to combine JavaScript and LLVM. Add an
additional LanguageStandard (this flag already supports C++03 and C++11) in
clang-format’s configuration and gate JavaScript specific formatting
decisions (e.g. indentation of JavaScript’s namespace-equivalent on it).

To make clang-format more useful to the LLVM project itself, support for
the tblgen language seems another worthy goal that can be achieved in the
same way as JavaScript.

Thoughts? Comments? Concerns with this direction?

If this is in line with LLVM’s/Clangs’s roadmap, we'll start working on the
few features missing for formatting JavaScript and we should have
rudimentary support towards the end of the year.

[1] http://en.wikipedia.org/wiki/C_(programming_language)
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