M-x company-diag出来是这样的：
Emacs 27.0.50 (x86_64-pc-linux-gnu) of 2018-11-06 on lilydjwg
Company 0.9.9
company-backends: ((company-auctex-macros company-auctex-symbols company-auctex-environments company-math-symbols-unicode company-math-symbols-latex company-reftex-citations company-reftex-labels)
company-auctex-bibs company-auctex-labels company-bbdb company-eclim company-semantic company-clang company-xcode company-cmake company-capf company-files
(company-dabbrev-code company-gtags company-etags company-keywords)
company-oddmuse company-dabbrev)
Used backend: (company-auctex-macros company-auctex-symbols company-auctex-environments company-math-symbols-unicode company-math-symbols-latex company-reftex-citations company-reftex-labels)
Major mode: latex-mode
Prefix: "doc"
Completions:
"documentclass"
"documentstyle"
AUCTeX配置是这样的：
(setq TeX-auto-save t)
(setq TeX-parse-self t)
(setq TeX-PDF-mode t)
(setq-default TeX-master nil)
(add-hook 'TeX-mode-hook
(lambda ()
(company-auctex-init)
(setcar company-backends
(let ((backend (car company-backends)))
(funcall (if (consp backend) 'append 'cons)
backend '(company-math-symbols-unicode
company-math-symbols-latex
company-reftex-citations
company-reftex-labels))))))
(add-hook 'TeX-mode 'company-mode-on)
(add-hook 'LaTeX-mode-hook 'visual-line-mode)
(add-hook 'LaTeX-mode-hook 'LaTeX-math-mode)
(add-hook 'LaTeX-mode-hook 'turn-on-reftex)