Regression: some other things are broken at startup with `syntax on`

[9ary]

Description

I noticed some things such as treesitter syntax highlighting and .editorconfig weren't applying at startup (when passing files as arguments to nvim).

I tracked the culprit down to this plugin and bisected the issue. The problematic commit is 2484f58. It seems reverting the function M.get() in that file fixes it.

Neovim version

0.9.5 and 0.10.0

Expected behavior

No response

Actual behavior

Things break on first read from command line.

Minimal config

local plugins = {
  ts         = 'https://github.com/nvim-treesitter/nvim-treesitter',
  ts_context = 'https://github.com/nvim-treesitter/nvim-treesitter-context',
  -- ADD ADDITIONAL PLUGINS THAT ARE _NECESSARY_ TO REPRODUCE THE ISSUE
}

for name, url in pairs(plugins) do
  local install_path = '/tmp/nvim/site/'..name
  if vim.fn.isdirectory(install_path) == 0 then
    vim.fn.system { 'git', 'clone', '--depth=1', url, install_path }
  end
  vim.o.runtimepath = install_path..','..vim.o.runtimepath
end

-- ADD INIT.LUA SETTINGS THAT IS _NECESSARY_ FOR REPRODUCING THE ISSUE

vim.cmd [[syntax on]]
require("treesitter-context").setup {
}

Steps to reproduce

An easy way to repro is to have a .editorconfig file like this:

root = true

[*]
max_line_length = 99

Open a file like nvim foo.c, and run :set tw?. With ts-context enabled, this returns 0, while without it returns 99 as expected.

This doesn't repro when reading files with :e.

[9ary]

Figured it out.

Call chain:

nvim-treesitter-context/lua/treesitter-context.lua

Line 205 in 5efba33

M.enable()

nvim-treesitter-context/lua/treesitter-context.lua

Line 161 in 5efba33

update()

nvim-treesitter-context/lua/treesitter-context.lua

Line 101 in 5efba33

local context, context_lines = get_context(bufnr, winid)

nvim-treesitter-context/lua/treesitter-context.lua

Line 57 in 5efba33

return require('treesitter-context.context').get(bufnr, winid)

nvim-treesitter-context/lua/treesitter-context/context.lua

Line 256 in 5efba33

if not pcall(vim.treesitter.get_parser, bufnr) then

into neovim code:
https://github.com/neovim/neovim/blob/6c3f7e7e27a0ffcf6d58dc1f5ad2fce7e59a2d88/runtime/lua/vim/treesitter.lua#L108
https://github.com/neovim/neovim/blob/6c3f7e7e27a0ffcf6d58dc1f5ad2fce7e59a2d88/runtime/lua/vim/treesitter.lua#L39

Indeed, minimal repro with no plugins:

bufnr = vim.api.nvim_get_current_buf()
vim.fn.bufload(bufnr)
local group = vim.api.nvim_create_augroup('testgroup', {})
vim.api.nvim_create_autocmd({ 'BufNewFile', 'BufRead', 'BufFilePost' }, {
  group = group,
  callback = function(args)
    print("hello world")
  end,
})

The autocmd never fires, because it was registered after bufload() was called!

The reason why this doesn't happen with syntax off is because vim.treesitter.get_parser() can't figure out the file's language in that case, and errors out.

Solution:

diff --git a/lua/treesitter-context/context.lua b/lua/treesitter-context/context.lua
index 5339c80..aaf5ae6 100644
--- a/lua/treesitter-context/context.lua
+++ b/lua/treesitter-context/context.lua
@@ -253,6 +253,14 @@ end
 --- @param winid integer
 --- @return Range4[]?, string[]?
 function M.get(bufnr, winid)
+  -- vim.treesitter.get_parser() calls bufload(), but we don't actually want to load the buffer:
+  -- this method is called during plugin init, before other plugins or the user's config
+  -- have a chance to initialize.
+  -- They may want to register autocmds, and this would prevent them from firing.
+  if vim.fn.bufloaded(bufnr) == 0 then
+    return
+  end
+
   if not pcall(vim.treesitter.get_parser, bufnr) then
     return
   end

I'll open a PR.

Also, the reason why this regressed. This is what it looked like before:

nvim-treesitter-context/lua/treesitter-context/context.lua

Lines 210 to 219 in b8b7e52

	function M.get(bufnr, winid)
	local max_lines = calc_max_lines(winid)
	if max_lines == 0 then
	return
	end
	if not pcall(vim.treesitter.get_parser, bufnr) then
	return
	end

calc_max_lines() always returns 0 at startup since the cursor is at the top of the window. This accidentally guarded get_parser() from being called so early, but it was removed in that commit.