Integrate asmfmt

[cespare]

This change integrates asmfmt support for .s files, in a similar way to how :GoFmt works.

Do take a careful look at this change; I'm not at all a vimscript expert.

[cespare]

/cc @klauspost just FYI

[fatih]

Thanks @cespare. I'm right now fixing my backlog of issues (FIFO order). I'll look into it.

[fatih]

Hi @cespare. This is amazing work. Thank you very much. So looking at it, it seems like we're treating any *.s file as asm. For formating itself, I think doing the following would be also sufficient:

let g:go_fmt_command = "asmfmt"

if get(g:, "go_fmt_autosave", 1)
  autocmd BufWritePre *.go,*.s call go#fmt#Format(-1)
endif

Doesn't this work? I'm just curious because theoretically it should work.

[cespare]

No, this doesn't work. It breaks formatting of Go files because asmfmt doesn't get the right filename, so it tries to format everything as asm.

We could probably get it to work by constructing a tempfile with the same file extension as the current file. However, I'm opposed to using asmfmt for formatting Go code from vim in general:

• If there's an improvement or bugfix to gofmt (or goimports, etc) you have to wait for that change to make it into asmfmt
• If you want to use some other gofmt variant that isn't bundled into asmfmt (it includes goimports and goreturns), you're out of luck

The changes I've made are bigger than what you've suggested, but it also makes it easy to add some better highlighting and indent files for Go asm in the future as well.

[fatih]

Got it. I don't have much to say, it's already a great work, and thanks again for the work, much appreciated 👍