Whishlist: TestGoFiles, XTestGoFiles command wrappers

[vbauerster]

There is :GoFiles command which lists the go files. I wish there to be similar commands for listing test files only, something like:
:GoTestFiles for go list -f '{{join .TestGoFiles "\n"}}'
:GoXTestFiles for go list -f '{{join .XTestGoFiles "\n"}}'

Default output of such listing commands is not very useful and not very readable. Therefore I propose to integrate such listing commands with fzf plugin seamlessly. For example, if fzf is installed, override :GoFiles to something like following and if there is no fzf, fallback to default.

command! FZFGoFiles call fzf#run(fzf#wrap({
    \ 'source': go#tool#Files(),
    \ 'options': '--preview "(highlight -O ansi {} || cat {}) 2> /dev/null | head -'.&lines.'"'
    \}))

(--preview option can be safely omitted)

[arp242]

I don't think that adding new commands is a good solution since there are 16 filetypes that can be looped over.

Instead, I created a PR to make go#tool#Files() and :GoFiles accept an argument which specifies which filestypes to list; see #1372.

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I'm not sure about the fzf integration... This seems like an entirely different thing? I'm not sure how this relates to listing test files etc.

[vbauerster]

Sounds reasonable and good! Well integrating with fzf is optional, because who is familiar with fzf, can do integration manually.