Why did syntax file in syntax plugin being executed twice when ft has been set?

[henry-hsieh]

Here is the minimal setup and a simple syntax plugin:

init.lua:

local lazypath = vim.fn.stdpath("data") .. "/lazy/lazy.nvim"
if not vim.loop.fs_stat(lazypath) then
  vim.fn.system({
    "git",
    "clone",
    "--filter=blob:none",
    "https://github.com/folke/lazy.nvim.git",
    "--branch=stable", -- latest stable release
    lazypath,
  })
end
vim.opt.rtp:prepend(lazypath)

require("lazy").setup({
  {
    dir = "~/test.vim/",
    ft = "test"
  },
})

Create a test.vim at home directory which following structure:

├── ftdetect
│   └── test.vim
├── ftplugin
│   └── test.vim
├── syntax
│   └── test.vim
└── indent
    └── test.vim

Content of ftdetect/test.vim:

autocmd BufNewFile,BufRead *.test setfiletype test

Content of ftplugin/test.vim:

" Only do this when not done yet for this buffer
if exists("b:did_ftplugin")
  finish
endif

" Don't load another plugin for this buffer
let b:did_ftplugin = 1

setlocal commentstring=//\ %s

" Undo the plugin effect
let b:undo_ftplugin = "setlocal com<"

echom "hi, ftplugin"

Content of syntax/test.vim:

" Only load this syntax file when no other was loaded.
if exists("b:current_syntax")
    finish
endif

" Don't load another syntax file for this buffer
let b:current_syntax = "test"

if !exists("b:syntax_other_checks")
  syn keyword testKeyword test
  let b:syntax_other_checks = 1
  let b:undo_ftplugin = "unlet! b:syntax_other_checks"
  echom "hi, syntax other checks"
endif
hi def link testKeyword Keyword

echom "hi, syntax"

Content of indent/test.vim:

" Only load this indent file when no other was loaded.
if exists("b:did_indent")
  finish
endif

" Don't load another indent file for this buffer
let b:did_indent = 1

setlocal indentkeys=o,O

" Undo the plugin effect
let b:undo_ftplugin = "setlocal indentkeys<"

echom "hi, indent"

---

Here is my Neovim version:

NVIM v0.9.4
Build type: Release
LuaJIT 2.1.1692716794

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/__w/neovim/neovim/build/nvim.AppDir/usr/share/nvim"

Run :checkhealth for more info

When I opened a hi.test file and it produced following messages (using :messages):

hi, ftplugin
hi, indent
hi, syntax other checks
hi, syntax
hi, syntax

Normally, Vim doesn't care the same highlight being set twice. However, if the plugin has other defined checks other than b:current_syntax, i.e. b:syntax_other_checks in syntax/test.vim, the plugin will not function correctly. In the example, the keyword highlight is defined in other checks. The highlight seems not having any effects (insert test in the editor, that is the only keyword of this plugin).

If I disabled lazy load, i.e., no ft = "test" in init.lua, the highlight is correctly displayed. The message becomes:

hi, ftplugin
hi, indent
hi, syntax other checks
hi, syntax

[dpetka2001]

Related #1406

[henry-hsieh]

Thanks for the information. If the behavior is unavoidable, it should be documented somewhere. The plugin author should notice such thing if they want to support lazy load.