Add support for linting git commit message files (#1233)

test/command_callback/test_gitlint_command_callback.vader

@@ -0,0 +1,84 @@
+Before:
+  Save g:ale_gitcommit_gitlint_executable
+  Save g:ale_gitcommit_gitlint_options
+  Save g:ale_gitcommit_gitlint_use_global
+
+  unlet! g:ale_gitcommit_gitlint_executable
+  unlet! g:ale_gitcommit_gitlint_options
+  unlet! g:ale_gitcommit_gitlint_use_global
+
+  runtime ale_linters/gitcommit/gitlint.vim
+  call ale#test#SetDirectory('/testplugin/test/command_callback')
+
+  let b:bin_dir = has('win32') ? 'Scripts' : 'bin'
+  let b:command_tail = ' lint'
+
+After:
+  Restore
+
+  call ale#test#RestoreDirectory()
+  call ale#linter#Reset()
+
+  unlet! b:bin_dir
+  unlet! b:executable
+
+Execute(The gitlint callbacks should return the correct default values):
+  AssertEqual
+  \ 'gitlint',
+  \ ale_linters#gitcommit#gitlint#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('gitlint') . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))
+
+Execute(The gitlint executable should be configurable, and escaped properly):
+  let g:ale_gitcommit_gitlint_executable = 'executable with spaces'
+
+  AssertEqual
+  \ 'executable with spaces',
+  \ ale_linters#gitcommit#gitlint#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('executable with spaces') . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))
+
+Execute(The gitlint command callback should let you set options):
+  let g:ale_gitcommit_gitlint_options = '--some-option'
+
+  AssertEqual
+  \ ale#Escape('gitlint') . ' --some-option' . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))
+
+Execute(The gitlint callbacks shouldn't detect virtualenv directories where they don't exist):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/no_virtualenv/subdir/foo/COMMIT_EDITMSG')
+
+  AssertEqual
+  \ 'gitlint',
+  \ ale_linters#gitcommit#gitlint#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('gitlint') . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))
+
+Execute(The gitlint callbacks should detect virtualenv directories):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/COMMIT_EDITMSG')
+
+  let b:executable = ale#path#Winify(
+  \ g:dir . '/python_paths/with_virtualenv/env/' . b:bin_dir . '/gitlint'
+  \)
+
+  AssertEqual
+  \ b:executable,
+  \ ale_linters#gitcommit#gitlint#GetExecutable(bufnr(''))
+
+  AssertEqual
+  \ ale#Escape(b:executable) . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))
+
+Execute(You should able able to use the global gitlint instead):
+  silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/COMMIT_EDITMSG')
+  let g:ale_gitcommit_gitlint_use_global = 1
+
+  AssertEqual
+  \ 'gitlint',
+  \ ale_linters#gitcommit#gitlint#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('gitlint') . b:command_tail,
+  \ ale_linters#gitcommit#gitlint#GetCommand(bufnr(''))