Add fourmolu fixer (#4501)

* Add fourmolu fixer

Fourmolu is aversion of Ormolu that supports configuration. This fixer
was modeled after the Ormolu one, but using the "stack executable"
approach of the Brittany and Stylish Haskell fixers.

* Sort supported-tools.md

autoload/ale/fix/registry.vim

@@ -561,6 +561,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['haskell'],
 \       'description': 'A formatter for Haskell source code.',
 \   },
+\   'fourmolu': {
+\       'function': 'ale#fixers#fourmolu#Fix',
+\       'suggested_filetypes': ['haskell'],
+\       'description': 'A formatter for Haskell source code.',
+\   },
 \   'jsonnetfmt': {
 \       'function': 'ale#fixers#jsonnetfmt#Fix',
 \       'suggested_filetypes': ['jsonnet'],

autoload/ale/fixers/fourmolu.vim

@@ -0,0 +1,20 @@
+call ale#Set('haskell_fourmolu_executable', 'fourmolu')
+call ale#Set('haskell_fourmolu_options', '')
+
+function! ale#fixers#fourmolu#GetExecutable(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'haskell_fourmolu_executable')
+
+    return ale#handlers#haskell_stack#EscapeExecutable(l:executable, 'fourmolu')
+endfunction
+
+function! ale#fixers#fourmolu#Fix(buffer) abort
+    let l:executable = ale#fixers#fourmolu#GetExecutable(a:buffer)
+    let l:options = ale#Var(a:buffer, 'haskell_fourmolu_options')
+
+    return {
+    \   'command': l:executable
+    \       . (empty(l:options) ? '' : ' ' . l:options)
+    \       . ' --stdin-input-file '
+    \       . ale#Escape(@%),
+    \}
+endfunction

doc/ale-haskell.txt

@@ -224,5 +224,25 @@ g:ale_haskell_ormolu_options                     *g:ale_haskell_ormolu_options*
   executable.
 
 
+===============================================================================
+fourmolu                                                 *ale-haskell-fourmolu*
+
+g:ale_haskell_fourmolu_executable           *g:ale_haskell_fourmolu_executable*
+                                            *b:ale_haskell_fourmolu_executable*
+  Type: |String|
+  Default: `'fourmolu'`
+
+  This variable can be changed to use a different executable for fourmolu.
+
+
+g:ale_haskell_fourmolu_options                 *g:ale_haskell_fourmolu_options*
+                                               *b:ale_haskell_fourmolu_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be used to pass extra options to the underlying fourmolu
+  executable.
+
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -236,6 +236,7 @@ Notes:
   * `cabal-ghc`
   * `cspell`
   * `floskell`
+  * `fourmolu`
   * `ghc`
   * `ghc-mod`
   * `hdevtools`

doc/ale.txt

@@ -3019,6 +3019,7 @@ documented in additional help files.
     stylish-haskell.......................|ale-haskell-stylish-haskell|
     hie...................................|ale-haskell-hie|
     ormolu................................|ale-haskell-ormolu|
+    fourmolu..............................|ale-haskell-fourmolu|
   hcl.....................................|ale-hcl-options|
     packer-fmt............................|ale-hcl-packer-fmt|
     terraform-fmt.........................|ale-hcl-terraform-fmt|

supported-tools.md

@@ -245,6 +245,7 @@ formatting.
   * [cabal-ghc](https://www.haskell.org/cabal/)
   * [cspell](https://github.com/streetsidesoftware/cspell/tree/main/packages/cspell)
   * [floskell](https://github.com/ennocramer/floskell)
+  * [fourmolu](https://github.com/fourmolu/fourmolu)
   * [ghc](https://www.haskell.org/ghc/)
   * [ghc-mod](https://github.com/DanielG/ghc-mod)
   * [hdevtools](https://hackage.haskell.org/package/hdevtools)

test/fixers/test_fourmolu_fixer_callback.vader

@@ -0,0 +1,29 @@
+Before:
+  Save g:ale_haskell_fourmolu_executable
+  Save g:ale_haskell_fourmolu_options
+
+After:
+  Restore
+
+Execute(The fourmolu callback should return the correct default values):
+  AssertEqual
+  \ {
+  \   'command': ale#Escape('fourmolu')
+  \     . ' --stdin-input-file '
+  \     . ale#Escape(@%)
+  \ },
+  \ ale#fixers#fourmolu#Fix(bufnr(''))
+
+Execute(The fourmolu executable and options should be configurable):
+  let g:ale_haskell_fourmolu_executable = '/path/to/fourmolu'
+  let g:ale_haskell_fourmolu_options = '-h'
+
+  AssertEqual
+  \ {
+  \   'command': ale#Escape('/path/to/fourmolu')
+  \     . ' -h'
+  \     . ' --stdin-input-file '
+  \     . ale#Escape(@%)
+  \ },
+  \ ale#fixers#fourmolu#Fix(bufnr(''))
+