fix(lsp): update the changetracking buffer state on reload

[icholy]

Fixes #24972

When a buffer is reloaded, each client is detached from that buffer and then re-attached:

neovim/runtime/lua/vim/lsp.lua

Lines 557 to 561 in 4e5c633

	changetracking.reset_buf(client, bufnr)
	if vim.tbl_get(client.server_capabilities, 'textDocumentSync', 'openClose') then
	client.notify(ms.textDocument_didClose, params)
	end
	client:_text_document_did_open_handler(bufnr)

When there’s only 1 LSP, the change tracking buffer state is deleted and re-created when the file is externally modified. This updates the buf_state.lines with the new buffer contents.

neovim/runtime/lua/vim/lsp/_changetracking.lua

Line 205 in 4e5c633

state.buffers[bufnr] = nil

If there are 2 LSPs attached, the buffer state is never deleted because the refs count never hits zero. So the buf state is never updated with the new buffer contents.

neovim/runtime/lua/vim/lsp/_changetracking.lua

Lines 202 to 204 in 4e5c633

	buf_state.refs = buf_state.refs - 1
	assert(buf_state.refs >= 0, 'refcount on buffer state must not get negative')
	if buf_state.refs == 0 then

[icholy]

I'm not sure how to test this.

[icholy]

I'm not attached to this implementation. If someone wants to suggest an alternate implementation or make a spin-off PR I'd be more than happy to test it out.

[icholy]

@mfussenegger I was looking through the history and it seems like you've done the most work in this area of the code. Any feedback would be appreciated.

[icholy]

Another way to fix this would be do change the on_reload callback to detach all the clients and then re-attach them all in a second pass. Removing all the clients would drop buf_state.refs to 0 and result in the lines being re-loaded. But this seems a little fragile.

on_reload = function()
  local params = { textDocument = { uri = uri } }
  local clients = lsp.get_clients({ bufnr = bufnr })
  for _, client in ipairs(clients) do
    changetracking.reset_buf(client, bufnr)
    if vim.tbl_get(client.server_capabilities, 'textDocumentSync', 'openClose') then
      client.notify(ms.textDocument_didClose, params)
    end
  end
  for _, client in ipairs(clients) do
    client:_text_document_did_open_handler(bufnr)
  end
end,

#28875

[icholy]

Closing in favor of #28875