Table of Contents

1. Current issue
2. Solutions

Current issue

The default option eldoc-message-commands covers the normal use case(already including self-insert-command. But it is not add c-electric-* by default, which means you will not get function signatures in cc-mode buffers after you insert an open bracket. Besides, when using eldoc along with completion frameworks like corfu, eldoc will not show up if it is displayed in echo erea.

Solutions

Use eldoc-add-command and eldoc-add-command-completions, but don't modify eldoc-message-commands directly.

(with-eval-after-load 'eldoc
  (eldoc-add-command-completions "c-electric-")
  (dolist (command '(corfu-insert corfu-quit))
    (eldoc-add-command command)))

There is another option eldoc-print-after-edit. But after it is set to t, eldoc will only be shown when editing.