Support formatting Nix

This adds support for formatting Nix code with the nixpkgs-fmt tool.

Author: flokli

README.md

@@ -28,6 +28,7 @@ helpfiles in the `doc/` directory. The helpfiles are also available via
 * TypeScript (clang-format)
 * Shell (shfmt)
 * [Vue](http://vuejs.org) (prettier)
+* Nix (nixpkgs-fmt)
 
 # Commands
 

autoload/codefmt/nixpkgs_fmt.vim

@@ -0,0 +1,49 @@
+" Copyright 2017 Google Inc. All rights reserved.
+"
+" Licensed under the Apache License, Version 2.0 (the "License");
+" you may not use this file except in compliance with the License.
+" You may obtain a copy of the License at
+"
+"     http://www.apache.org/licenses/LICENSE-2.0
+"
+" Unless required by applicable law or agreed to in writing, software
+" distributed under the License is distributed on an "AS IS" BASIS,
+" WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+" See the License for the specific language governing permissions and
+" limitations under the License.
+
+
+let s:plugin = maktaba#plugin#Get('codefmt')
+
+
+""
+" @private
+"
+" Formatter provider for .nix files using nixpkgs-fmt.
+function! codefmt#nixpkgs_fmt#GetFormatter() abort
+  let l:formatter = {
+      \ 'name': 'nixpkgs-fmt',
+      \ 'setup_instructions': 'Install nixpkgs-fmt. ' .
+          \ '(https://github.com/nix-community/nixpkgs-fmt).'}
+
+  function l:formatter.IsAvailable() abort
+    return executable(s:plugin.Flag('nixpkgs_fmt_executable'))
+  endfunction
+
+  function l:formatter.AppliesToBuffer() abort
+    return &filetype is# 'nix'
+  endfunction
+
+  ""
+  " Reformat the current buffer with nixpkgs-fmt or the binary named in
+  " @flag(nixpkgs_fmt_executable)
+  " @throws ShellError
+  function l:formatter.Format() abort
+    let l:cmd = [ s:plugin.Flag('nixpkgs_fmt_executable') ]
+
+    " nixpkgs-fmt does not support range formatting.
+    call codefmt#formatterhelpers#Format(l:cmd)
+  endfunction
+
+  return l:formatter
+endfunction

instant/flags.vim

@@ -168,3 +168,7 @@ call s:plugin.Flag('zprint_executable', 'zprint')
 ""
 " The path to the fish_indent executable.
 call s:plugin.Flag('fish_indent_executable', 'fish_indent')
+
+""
+" The path to the nixpkgs-fmt executable.
+call s:plugin.Flag('nixpkgs_fmt_executable', 'nixpkgs-fmt')

plugin/register.vim

@@ -38,3 +38,4 @@ call s:registry.AddExtension(codefmt#googlejava#GetFormatter())
 call s:registry.AddExtension(codefmt#shfmt#GetFormatter())
 call s:registry.AddExtension(codefmt#zprint#GetFormatter())
 call s:registry.AddExtension(codefmt#fish_indent#GetFormatter())
+call s:registry.AddExtension(codefmt#nixpkgs_fmt#GetFormatter())

vroom/nixpkgs_fmt.vroom

@@ -0,0 +1,50 @@
+The built-in nixpkgs-fmt formatter knows how to format Nix code.
+If you aren't familiar with basic codefmt usage yet, see main.vroom first.
+
+We'll set up codefmt and configure the vroom environment, then jump into some
+examples.
+
+  :source $VROOMDIR/setupvroom.vim
+
+  :let g:repeat_calls = []
+  :function FakeRepeat(...)<CR>
+  |  call add(g:repeat_calls, a:000)<CR>
+  :endfunction
+  :call maktaba#test#Override('repeat#set', 'FakeRepeat')
+
+  :call codefmt#SetWhetherToPerformIsAvailableChecksForTesting(0)
+
+
+The nixpkgs-fmt formatter expects the nixpkgs-fmt executable to be installed on
+your system.
+
+  % f()
+  :FormatCode nixpkgs-fmt
+  ! nixpkgs-fmt .*
+  $ f()
+
+The name or path of the nixpkgs-fmt executable can be configured via the
+nixpkgs_fmt_executable flag if the default of "nixpkgs-fmt" doesn't work.
+
+  :Glaive codefmt nixpkgs_fmt_executable='nixpkgsfmt'
+  :FormatCode nixpkgs-fmt
+  ! nixpkgsfmt .*
+  $ f()
+  :Glaive codefmt nixpkgs_fmt_executable='nixpkgs-fmt'
+
+
+You can format any buffer with nixpkgs-fmt specifying the formatter explicitly.
+Here's an example:
+
+  @clear
+  % { foo = "bar" ;}
+
+  :FormatCode nixpkgs-fmt
+  ! nixpkgs-fmt .*
+  $ {
+  $   foo = "bar";
+  $ }
+  {
+    foo = "bar";
+  }
+  @end