Company-dabbrev does not work on eglot

Question

I use emacs 28/29 on windows. this is my config.

(use-package company
  :ensure t
  :pin gnu
  :init (global-company-mode)
  :config
  (setq company-backends '(company-dabbrev)
    company-idle-delay 0
    company-echo-delay 0))

(use-package eglot
  :ensure t
  :commands (eglot eglot-ensure eglot-server-programs)
  :hook ((c-mode . eglot-ensure)
         (c++-mode . eglot-ensure))
  :config
  (add-hook 'eglot-mode-hook (lambda () (setq-local
                     company-backends '(company-dabbrev
                                ;; company-capf
                                ))))
  (add-to-list 'eglot-server-programs '((c++-mode c-mode) "D:/LLVM/bin/clangd.exe"))
  (add-hook 'eglot--managed-mode-hook (lambda () (flymake-mode -1))))

Answer 1

The company-mode polls each backend until one of them can provide completions. However, the lsp/eglot with the capf backend is not sure if it can provide completions (it needs to wait for the lsp-server to respond), so it tells the company I have candidates by default. This results in later backends not being used, even if the lsp-server does not return any completion in the end.

Solutions include merging multiple backends by :with or considering super-capf from package cape.

Attention: The above answer is my recollection and I can't find the source for now, maybe at the discussion or issue of company-mode.