vim-patch:8.0.1395: it is not easy to see if a colorscheme is well written

Problem:    It is not easy to see if a colorscheme is well written.
Solution:   Add a script that checks for common mistakes. (Christian Brabandt)
200d0e36bc

runtime/colors/README.txt

@@ -64,6 +64,7 @@ Search for "highlight_init".
 If you think you have a color scheme that is good enough to be used by others,
 please check the following items:
 
+- Source the check_colors.vim script to check for common mistakes.
 - Does it work in a color terminal as well as in the GUI?
 - Is "g:colors_name" set to a meaningful value?  In case of doubt you can do
   it this way:

runtime/colors/check_colors.vim

@@ -0,0 +1,136 @@
+" This script tests a color scheme for some errors. Load the scheme and source
+" this script. e.g. :e colors/desert.vim | :so test_colors.vim
+" Will output possible errors.
+
+let s:save_cpo= &cpo
+set cpo&vim
+
+func! Test_check_colors()
+  call cursor(1,1)
+  let err={}
+
+  " 1) Check g:colors_name is existing
+  if !search('\<\%(g:\)\?colors_name\>', 'cnW')
+    let err['colors_name'] = 'g:colors_name not set'
+  else
+    let err['colors_name'] = 'OK'
+  endif
+
+  " 2) Check for some well-defined highlighting groups
+  " Some items, check several groups, e.g. Diff, Spell
+  let hi_groups = ['ColorColumn', 'Diff', 'ErrorMsg', 'Folded',
+        \ 'FoldColumn', 'IncSearch', 'LineNr', 'ModeMsg', 'MoreMsg', 'NonText',
+        \ 'Normal', 'Pmenu', 'Todo', 'Search', 'Spell', 'StatusLine', 'TabLine',
+        \ 'Title', 'Visual', 'WarningMsg', 'WildMenu']
+  let groups={}
+  for group in hi_groups
+    if search('\c@suppress\s\+'.group, 'cnW')
+      " skip check, if the script contains a line like
+      " @suppress Visual:
+      let groups[group] = 'Ignoring '.group
+      continue
+    endif
+    if !search('hi\%[ghlight] \+'.group, 'cnW')
+      let groups[group] = 'No highlight definition for '.group
+      continue
+    endif
+    if !search('hi\%[ghlight] \+'.group. '.*fg=', 'cnW')
+      let groups[group] = 'Missing foreground color for '.group
+      continue
+    endif
+    if search('hi\%[ghlight] \+'.group. '.*guibg=', 'cnW') &&
+        \ !search('hi\%[ghlight] \+'.group. '.*ctermbg=', 'cnW')
+      let groups[group] = 'Missing bg terminal color for '.group
+      continue
+    endif
+    call search('hi\%[ghlight] \+'.group, 'cW')
+    " only check in the current line
+    if !search('guifg', 'cnW', line('.'))   || !search('ctermfg', 'cnW', line('.'))
+      " do not check for background colors, they could be intentionally left out
+      let groups[group] = 'Missing fg definition for '.group
+    endif
+    call cursor(1,1)
+  endfor
+  let err['highlight'] = groups
+
+  " 3) Check, that it does not set background highlighting
+  " Doesn't ':hi Normal ctermfg=253 ctermfg=233' also set the background sometimes?
+  let bg_set='\(set\?\|setl\(ocal\)\?\) .*\(background\|bg\)=\(dark\|light\)'
+  let bg_let='let \%([&]\%([lg]:\)\?\)\%(background\|bg\)\s*=\s*\([''"]\?\)\w\+\1'
+  let bg_pat='\%('.bg_set. '\|'.bg_let.'\)'
+  let line=search(bg_pat, 'cnW')
+  if search(bg_pat, 'cnW')
+    exe line
+    if search('hi \U\w\+\s\+\S', 'cbnW')
+      let err['background'] = 'Should not set background option after :hi statement'
+    endif
+  else
+    let err['background'] = 'OK'
+  endif
+  call cursor(1,1)
+
+  " 4) Check, that t_Co is checked
+  let pat = '[&]t_Co\s*[<>=]=\?\s*\d\+'
+  if !search(pat, 'ncW')
+    let err['t_Co'] = 'Does not check terminal for capable colors'
+  endif
+
+  " 5) Initializes correctly, e.g. should have a section like
+  " hi clear
+  " if exists("syntax_on")
+  " syntax reset
+  " endif
+  let pat='hi\%[ghlight]\s*clear\n\s*if\s*exists(\([''"]\)syntax_on\1)\n\s*syn\%[tax]\s*reset\n\s*endif'
+  if !search(pat, 'cnW')
+    let err['init'] = 'No initialization'
+  endif
+
+  " 6) Does not use :syn on
+  if search('syn\%[tax]\s\+on', 'cnW')
+    let err['background'] = 'Should not issue :syn on'
+  endif
+
+  " 7) Does not define filetype specfic groups like vimCommand, htmlTag,
+  let hi_groups = ['vim', 'html', 'python', 'sh', 'ruby']
+  for group in hi_groups
+    let pat='\Chi\%[ghlight]\s*\zs'.group.'\w\+\>'
+    if search(pat, 'cnW')
+      let line = search(pat, 'cW')
+      let err['filetype'] = get(err, 'filetype', 'Should not define: ') . matchstr(getline('.'), pat). ' '
+    endif
+    call cursor(1,1)
+  endfor
+  let g:err = err
+
+  " print Result
+  call Result(err)
+endfu
+
+fu! Result(err)
+  let do_roups = 0
+  echohl Title|echomsg "---------------"|echohl Normal
+  for key in sort(keys(a:err))
+    if key is# 'highlight'
+      let do_groups = 1
+      continue
+    else
+      if a:err[key] !~ 'OK'
+        echohl Title
+      endif
+      echomsg printf("%15s: %s", key, a:err[key])
+      echohl Normal
+    endif
+  endfor
+  echohl Title|echomsg "---------------"|echohl Normal
+  if do_groups
+    echohl Title | echomsg "Groups" | echohl Normal
+    for v1 in sort(keys(a:err['highlight']))
+      echomsg printf("%25s: %s", v1, a:err['highlight'][v1])
+    endfor
+  endif
+endfu
+
+call Test_check_colors()
+
+let &cpo = s:save_cpo
+unlet s:save_cpo