Why colorscheme is re-loaded if vimrc is located in $VIM?

Question

I ran into a problem with cursor color being reset when using gruvbox color scheme on both Linux and Windows. During debugging I discovered that the color scheme is reloaded if vimrc is located in $VIM. In my test case I have only two user files: vimrc and $VIM/vimfiles/colors/kgb.vim (the rest is the standard vim installation). I set VIMINIT to "source $VIM\vimrc" to control which vimrc is loaded.

set|grep VIM
MYVIMRC=C:\Users\Public\Vim\vimrc
VIM=C:\Users\Public\Vim
VIMINIT=source C:\Users\Public\Vim\vimrc
VIMRUNTIME=E:\Vim\vim81

cd %VIM%

find vim*
vimfiles
vimfiles/colors
vimfiles/colors/kgb.vim
vimrc

cat vimrc
echomsg "Before colo: " . execute("colo")
color kgb
echomsg "After colo: " . execute("colo")

cat vimfiles/colors/kgb.vim
echomsg "Executing script: " . expand("<sfile>")
let g:colors_name="kgb"

gvim.exe

:mes
Before colo: ^@default
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim
After colo: ^@kgb
Before colo: ^@kgb
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim
After colo: ^@kgb
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim

NOTE: The above output shows that vimrc is loaded twice and colorscheme is loaded three times in Windows (only two times on Linux). If VIMINIT is not set and vimrc is located in $VIM, then vimrc is loaded only once, but colorsheme is still loaded twice on both Windows and Linux.

:scr
  1: C:\Users\Public\Vim\vimrc
  2: C:\Users\Public\Vim\vimfiles\colors\kgb.vim
  3: E:\Vim\vim81\plugin\getscriptPlugin.vim
  4: E:\Vim\vim81\plugin\gzip.vim
  5: E:\Vim\vim81\plugin\logiPat.vim
  6: E:\Vim\vim81\plugin\manpager.vim
  7: E:\Vim\vim81\plugin\matchparen.vim
  8: E:\Vim\vim81\plugin\netrwPlugin.vim
  9: E:\Vim\vim81\plugin\rrhelper.vim
 10: E:\Vim\vim81\plugin\spellfile.vim
 11: E:\Vim\vim81\plugin\tarPlugin.vim
 12: E:\Vim\vim81\plugin\tohtml.vim
 13: E:\Vim\vim81\plugin\vimballPlugin.vim
 14: E:\Vim\vim81\plugin\zipPlugin.vim
 15: E:\Vim\vim81\menu.vim
 16: E:\Vim\vim81\autoload\paste.vim

:quit
Error:
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim

If I move vimrc under vimfiles and set VIMINIT="source $VIM\vimfiles\vimrc" the scheme is loaded only once:

set|grep VIM
MYVIMRC=C:\Users\Public\Vim\vimfiles\vimrc
VIM=C:\Users\Public\Vim
VIMINIT=source C:\Users\Public\Vim\vimfiles\vimrc
VIMRUNTIME=E:\Vim\vim81

gvim.exe

:mes
Before colo: ^@default
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim
After colo: ^@kgb
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim

:quit
Error:
Executing script: C:\Users\Public\Vim\vimfiles\colors\kgb.vim

Any explanation why this is happening?

Answer 1

Why the colorscheme is loaded twice

This is slightly speculative, since your excellent and detailed question nevertheless still doesn't contain quite enough information about your setup to be certain, but I believe what is happening is this:

1. When Vim starts up, one of the first things it does is load your $VIM/vimrc file, which loads your colorscheme, thus setting g:colors_name. However, note that $VIM/vimrc is not considered a user vimrc file, but is instead a system vimrc. (See :help system-vimrc and check the output of :version to confirm that Vim is using this location for its system vimrc.)

2. Presuming you don't have another vimrc in any of the locations described in :help _vimrc point 3.c.II, then Vim will then load the defaults.vim file, as described in point 3.c.V, because no user vimrc has been found.

3. defaults.vim executes the command :syntax on, which sources the file $VIMRUNTIME/syntax/syntax.vim.

4. syntax.vim executes the command :runtime syntax/synload.vim, which will find and source the file $VIMRUNTIME/syntax/synload.vim.

5. synload.vim contains the following code:

   " Set the default highlighting colors.  Use a color scheme if specified.
   if exists("colors_name")
     exe "colors " . colors_name
   

   colors_name was set in Step 1, so execution enters the if block, the :colorscheme command is run, and your colorscheme is reloaded.

If you view the output of the command :scriptnames, you should be able to trace (roughly) the execution of Vim's startup procedure through these files.

How to fix your problem

There are several ways you could prevent the double-load, but there's a simpler and more robust method of solving your actual issue, which is that you want to ensure your cursor color is set correctly. You can do this by setting up an autocommand that fires whenever the colorscheme is set e.g.:

augroup SetCursorColor
  autocmd!
  autocmd ColorScheme * highlight Cursor guibg=red guifg=NONE
augroup END

The pattern is matched against the colorscheme name, so if you only want to use this cursor colour in gruvbox, you can specify this like so:

autocmd ColorScheme gruvbox highlight Cursor guibg=red guifg=NONE