Fix 3103 - add shellcheck shell directive detection.

autoload/ale/handlers/shellcheck.vim

@@ -1,8 +1,32 @@
 " Author: w0rp <devw0rp@gmail.com>
 " Description: This file adds support for using the shellcheck linter
 
+" Shellcheck supports shell directives to define the shell dialect for scripts
+" that do not have a shebang for some reason.
+" https://github.com/koalaman/shellcheck/wiki/Directive#shell
+function! ale#handlers#shellcheck#GetShellcheckDialectDirective(buffer) abort
+    let l:linenr = 0
+    let l:pattern = '\s\{-}#\s\{-}shellcheck\s\{-}shell=\(.*\)'
+    let l:possible_shell = ['bash', 'dash', 'ash', 'tcsh', 'csh', 'zsh', 'ksh', 'sh']
+
+    while l:linenr < min([50, line('$')])
+        let l:linenr += 1
+        let l:match = matchlist(getline(l:linenr), l:pattern)
+
+        if len(l:match) > 1 && index(l:possible_shell, l:match[1]) >= 0
+            return l:match[1]
+        endif
+    endwhile
+
+    return ''
+endfunction
+
 function! ale#handlers#shellcheck#GetDialectArgument(buffer) abort
-    let l:shell_type = ale#handlers#sh#GetShellType(a:buffer)
+    let l:shell_type = ale#handlers#shellcheck#GetShellcheckDialectDirective(a:buffer)
+
+    if empty(l:shell_type)
+        let l:shell_type = ale#handlers#sh#GetShellType(a:buffer)
+    endif
 
     if !empty(l:shell_type)
         " Use the dash dialect for /bin/ash, etc.

test/test_shell_detection.vader

@@ -117,3 +117,51 @@ Execute(The dash dialect should be used for the shell and the base function):
 
 Execute(dash should be used for shellcheck):
   AssertEqual 'dash', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a Bash shellcheck shell directive):
+  # shellcheck shell=bash
+
+Execute(bash dialect should be detected appropriately):
+  AssertEqual 'bash', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a sh shellcheck shell directive):
+  #shellcheck   shell=sh
+
+Execute(sh dialect should be detected appropriately):
+  AssertEqual 'sh', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a tcsh shellcheck shell directive):
+  #   shellcheck   shell=tcsh
+
+Execute(tcsh dialect should be detected appropriately):
+  AssertEqual 'tcsh', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a zsh shellcheck shell directive):
+  #   shellcheck shell=zsh
+
+Execute(zsh dialect should be detected appropriately):
+  AssertEqual 'zsh', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a csh shellcheck shell directive):
+  # shellcheck shell=csh
+
+Execute(zsh dialect should be detected appropriately):
+  AssertEqual 'csh', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a ksh shellcheck shell directive):
+  # shellcheck shell=ksh
+
+Execute(ksh dialect should be detected appropriately):
+  AssertEqual 'ksh', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a dash shellcheck shell directive):
+  # shellcheck shell=dash
+
+Execute(dash dialect should be detected appropriately):
+  AssertEqual 'dash', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))
+
+Given(A file with a ash shellcheck shell directive):
+  # shellcheck shell=ash
+
+Execute(dash dialect should be detected for ash that shellcheck does not support):
+  AssertEqual 'dash', ale#handlers#shellcheck#GetDialectArgument(bufnr(''))