Missing "shellcheck shell={dialect}" detection

[lloeki]

Information

VIM version

VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Mar 11 2020 13:48:59)
macOS version
Included patches: 1-343

Operating System: macOS 10.15

What went wrong

Opening a shell file with shellcheck shell=bash lints with shellcheck -s sh.

Reproducing the bug

$ cat > foo <<EOF
# vim: ft=sh
# shellcheck shell=bash
function foo(){
  true
}
EOF
$ vim foo  # shows SC2112

=> ALE orders spellcheck to lint as sh

Seems like in ale_linters#sh#shellcheck#GetDialectArgument(buffer) there's a vim-level workaround possible by writing my own autocmd to set some buffer variables, but my vimscript-fu is terrible:

    " If there's no hashbang, try using Vim's buffer variables.
    if getbufvar(a:buffer, 'is_bash', 0)
        return 'bash'
    elseif getbufvar(a:buffer, 'is_sh', 0)
        return 'sh'
    elseif getbufvar(a:buffer, 'is_kornshell', 0)
        return 'ksh'
    endif

But from a cursory look I suppose ale#handlers#sh#GetShellType(buffer) ought to be modified to look for shellcheck shell={dialect} in the first few lines (again my vimscript-fu is appalling, otherwise I'd have made a PR 😅).

:ALEInfo

Current Filetype: sh
Available Linters: ['language_server', 'shell', 'shellcheck']
  Enabled Linters: ['language_server', 'shell', 'shellcheck']
 Suggested Fixers: 
  'remove_trailing_lines' - Remove all blank lines at the end of a file.
  'shfmt' - Fix sh files with shfmt.
  'trim_whitespace' - Remove all trailing whitespace characters at the end of every line.
 Linter Variables:

let g:ale_sh_language_server_executable = 'bash-language-server'
let g:ale_sh_language_server_use_global = 0
let g:ale_sh_shell_default_shell = 'zsh'
let g:ale_sh_shellcheck_change_directory = 1
let g:ale_sh_shellcheck_dialect = 'auto'
let g:ale_sh_shellcheck_exclusions = ''
let g:ale_sh_shellcheck_executable = 'shellcheck'
let g:ale_sh_shellcheck_options = ''
 Global Variables:

let g:ale_cache_executable_check_failures = v:null
let g:ale_change_sign_column_color = 0
let g:ale_command_wrapper = ''
let g:ale_completion_delay = v:null
let g:ale_completion_enabled = 0
let g:ale_completion_max_suggestions = v:null
let g:ale_echo_cursor = 1
let g:ale_echo_msg_error_str = 'Error'
let g:ale_echo_msg_format = '%code: %%s'
let g:ale_echo_msg_info_str = 'Info'
let g:ale_echo_msg_warning_str = 'Warning'
let g:ale_enabled = 1
let g:ale_fix_on_save = 0
let g:ale_fixers = {}
let g:ale_history_enabled = 1
let g:ale_history_log_output = 1
let g:ale_keep_list_window_open = 0
let g:ale_lint_delay = 200
let g:ale_lint_on_enter = 1
let g:ale_lint_on_filetype_changed = 1
let g:ale_lint_on_insert_leave = 1
let g:ale_lint_on_save = 1
let g:ale_lint_on_text_changed = 'normal'
let g:ale_linter_aliases = {}
let g:ale_linters = {}
let g:ale_linters_explicit = 0
let g:ale_list_vertical = 0
let g:ale_list_window_size = 10
let g:ale_loclist_msg_format = '%code: %%s'
let g:ale_lsp_root = {}
let g:ale_max_buffer_history_size = 20
let g:ale_max_signs = -1
let g:ale_maximum_file_size = v:null
let g:ale_open_list = 0
let g:ale_pattern_options = v:null
let g:ale_pattern_options_enabled = v:null
let g:ale_set_balloons = 0
let g:ale_set_highlights = 1
let g:ale_set_loclist = 1
let g:ale_set_quickfix = 0
let g:ale_set_signs = 1
let g:ale_sign_column_always = 0
let g:ale_sign_error = '✖'
let g:ale_sign_info = '⚠'
let g:ale_sign_offset = 1000000
let g:ale_sign_style_error = '✖'
let g:ale_sign_style_warning = '⚠'
let g:ale_sign_warning = '⚠'
let g:ale_sign_highlight_linenrs = 0
let g:ale_statusline_format = v:null
let g:ale_type_map = {}
let g:ale_use_global_executables = v:null
let g:ale_virtualtext_cursor = 0
let g:ale_warn_about_trailing_blank_lines = 1
let g:ale_warn_about_trailing_whitespace = 1
  Command History:

(executable check - success) zsh
(finished - exit code 0) ['/bin/zsh', '-c', 'zsh -n ''/var/folders/hx/6nb5k_jn6mn8v6ch4xh6937c0000gp/T/vC3jppQ/2/foo''']

<<<NO OUTPUT RETURNED>>>

(executable check - success) shellcheck
(finished - exit code 0) ['/bin/zsh', '-c', '''shellcheck'' --version']

<<<OUTPUT STARTS>>>
ShellCheck - shell script analysis tool
version: 0.7.0
license: GNU General Public License, version 3
website: https://www.shellcheck.net
<<<OUTPUT ENDS>>>

(finished - exit code 1) ['/bin/zsh', '-c', 'cd ''/Users/lloeki'' && ''shellcheck'' -s sh -x -f gcc - < ''/var/folders/hx/6nb5k_jn6mn8v6ch4xh6937c0000gp/T/vC3jppQ/3/foo''']

<<<OUTPUT STARTS>>>
-:3:1: warning: 'function' keyword is non-standard. Delete it. [SC2112]
<<<OUTPUT ENDS>>>

[lloeki]

Actually came up with this limited workaround:

function! ShellcheckDetect(buffer)
  for l:line_num in [1, 2, 3]
    let l:line = get(getbufline(a:buffer, l:line_num), 0, '')

    if l:line[:11] is# '# shellcheck'
      let l:command = l:line
      for l:possible_shell in ['bash', 'dash', 'ash', 'tcsh', 'csh', 'zsh', 'ksh', 'sh']
        if l:command =~# l:possible_shell . '\s*$'
          return l:possible_shell
        endif
      endfor
    endif
  endfor

  return ''
endfunction

function! ShellcheckSet(buffer)
  let l:shell = ShellcheckDetect(a:buffer)
  if l:shell == 'bash'
    call setbufvar(a:buffer, 'is_bash', 1)
  else
    call setbufvar(a:buffer, 'is_bash', 0)
  endif
endfunction

autocmd FileType sh call ShellcheckSet(bufnr("%"))

[hsanson]

@lloeki I have create a PR that adds support to shellcheck shell directives for dialect detection.