不知道是不是想要这样的效果：
配置：
(yc/defmacro yc/add-company-backends-with-yasnippet (&rest backends)
`(set (make-local-variable 'company-backends)
(push ',(append backends '(company-yasnippet :separate)) company-backends)))
(use-package lsp-mode
:custom
(lsp-enable-indentation nil)
(lsp-auto-configure nil)))
(defun yc/lsp-adv (&rest args)
"Advice for 'lsp'： update company backends, and enable flyckcheck."
;; functions to run after lsp...
(lsp-ui-flycheck-enable t)
(yc/add-company-backends-with-yasnippet company-lsp)
(flycheck-mode 1))
(advice-add 'lsp :after #'yc/lsp-adv)
这是 lsp 启用后， company-backends的值：
((company-lsp company-yasnippet :separate) (company-keywords company-dabbrev-code company-yasnippet :separate) (company-files company-dabbrev company-abbrev :with company-yasnippet))