Add initial support for settings to overwrite ale shell

autoload/ale/job.vim

@@ -11,6 +11,12 @@
 " A setting for wrapping commands.
 let g:ale_command_wrapper = get(g:, 'ale_command_wrapper', '')
 
+" A setting for the shell used to execute commands
+let g:ale_shell = get(g:, 'ale_shell', &shell)
+
+" A setting for the arguments we pass to the shell when executing commands
+let g:ale_shell_arguments = get(g:, 'ale_shell_arguments', &shellcmdflag)
+
 if !has_key(s:, 'job_map')
     let s:job_map = {}
 endif
@@ -188,11 +194,11 @@ function! ale#job#PrepareCommand(buffer, command) abort
         return 'cmd /s/c "' . l:command . '"'
     endif
 
-    if &shell =~? 'fish$\|pwsh$'
+    if g:ale_shell =~? 'fish$\|pwsh$'
-        return ['/bin/sh', '-c', l:command]
+        return ['/bin/sh', g:ale_shell_arguments, l:command]
     endif
 
-    return split(&shell) + split(&shellcmdflag) + [l:command]
+    return [g:ale_shell] + split(g:ale_shell_arguments) + [l:command]
 endfunction
 
 " Start a job with options which are agnostic to Vim and NeoVim.

doc/ale.txt

@@ -1984,6 +1984,24 @@ g:ale_windows_node_executable_path         *g:ale_windows_node_executable_path*
   scripts are executed with whatever executable is configured with this
   setting.
 
+g:ale_shell                                                      *g:ale_shell*
+
+  Type: |String|
+  Default: `'&shell'`
+
+  This variable is used to determine which shell ale will use to execute 
+  commands. This variables defaults to the value of the vim option '&shell'
+  which corresponds to the $SHELL environment variable. For example 
+  if `$SHELL == '/bin/bash'`, but you want to use zsh, set `g:ale_shell = '/bin/zsh'.`
+
+g:ale_shell_arguments                                  *g:ale_shell_arguments*
+
+  Type: |String|
+  Default: `'&shellcmdflag'`
+
+  This variable is used to determine what commands vim will pass to the shell
+  to execute it's commands. By default, `&shellcmdflag` would be set to the
+  value of '`-c'`.
 
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 6.1. Highlights                                                *ale-highlights*