Add erlang-mode fixer for Erlang files (#4848)

This fixer performs indentation with the Erlang mode for Emacs.
The Erlang mode is maintained in the Erlang/OTP source tree.  It indents
some things differently than the Vim indent plugin, and provides more
customization options.

autoload/ale/fix/registry.vim

@@ -98,6 +98,12 @@ let s:default_registry = {
 \       'suggested_filetypes': ['dune'],
 \       'description': 'Fix dune files with dune format',
 \   },
+\   'erlang_mode': {
+\       'function': 'ale#fixers#erlang_mode#Fix',
+\       'suggested_filetypes': ['erlang'],
+\       'description': 'Indent with the Erlang mode for Emacs',
+\       'aliases': ['erlang-mode'],
+\   },
 \   'fecs': {
 \       'function': 'ale#fixers#fecs#Fix',
 \       'suggested_filetypes': ['javascript', 'css', 'html'],

autoload/ale/fixers/erlang_mode.vim

@@ -0,0 +1,49 @@
+" Author: Dmitri Vereshchagin <dmitri.vereshchagin@gmail.com>
+" Description: Indent with the Erlang mode for Emacs
+
+call ale#Set('erlang_erlang_mode_emacs_executable', 'emacs')
+call ale#Set('erlang_erlang_mode_indent_level', 4)
+call ale#Set('erlang_erlang_mode_icr_indent', 'nil')
+call ale#Set('erlang_erlang_mode_indent_guard', 2)
+call ale#Set('erlang_erlang_mode_argument_indent', 2)
+call ale#Set('erlang_erlang_mode_indent_tabs_mode', 'nil')
+
+let s:variables = {
+\   'erlang-indent-level': 'erlang_erlang_mode_indent_level',
+\   'erlang-icr-indent': 'erlang_erlang_mode_icr_indent',
+\   'erlang-indent-guard': 'erlang_erlang_mode_indent_guard',
+\   'erlang-argument-indent': 'erlang_erlang_mode_argument_indent',
+\   'indent-tabs-mode': 'erlang_erlang_mode_indent_tabs_mode',
+\}
+
+function! ale#fixers#erlang_mode#Fix(buffer) abort
+    let emacs_executable =
+    \   ale#Var(a:buffer, 'erlang_erlang_mode_emacs_executable')
+
+    let l:exprs = [
+    \   s:SetqDefault(a:buffer, s:variables),
+    \   '(erlang-mode)',
+    \   '(font-lock-fontify-region (point-min) (point-max))',
+    \   '(indent-region (point-min) (point-max))',
+    \   '(funcall (if indent-tabs-mode ''tabify ''untabify)'
+    \         . ' (point-min) (point-max))',
+    \   '(save-buffer 0)',
+    \]
+
+    let l:command = ale#Escape(l:emacs_executable)
+    \   . ' --batch'
+    \   . ' --find-file=%t'
+    \   . join(map(l:exprs, '" --eval=" . ale#Escape(v:val)'), '')
+
+    return {'command': l:command, 'read_temporary_file': 1}
+endfunction
+
+function! s:SetqDefault(buffer, variables) abort
+    let l:args = []
+
+    for [l:emacs_name, l:ale_name] in items(a:variables)
+        let l:args += [l:emacs_name, ale#Var(a:buffer, l:ale_name)]
+    endfor
+
+    return '(setq-default ' . join(l:args) . ')'
+endfunction