Fix a few issues with the Emacs mode definition.
First, in 1ab7789f3 (2021-10-13, Emacs: Protobuf mode should be derived from
prog-mode) we made `protobuf-mode' a derived mode of `prog-mode' using the
`define-derived-mode' macro[1]. However, the definition body was not updated
accordingly. So in this commit, we:
- Remove the superfluous `(interactive)' form;
- Remove the unnecessary call of `kill-all-local-variables', which is already
handled by `define-derived-mode' and could cause a few issues, for example,
it prevents `prog-mode-hook' from being run;
- Remove forms that set `major-mode' and `mode-name', which are automatically
set to the first and third arguments respectively;
- Remove forms that set key map, syntax table, and abbrev table, which are
already handled automatically;
- Do not run `protobuf-mode-hook' explicitly in the body. It is already arranged
to be run after the body.
Second, the call to `c-make-emacs-variables-local' is removed. It is called
inside `c-init-language-vars' already. Calling it again should do no harm now,
but to be future-proof it might be better to just remove it.
Finally, we move the `c-update-modeline' form to the :after-hook argument to
ensure it is run at the very end, so that the mode line will reflect all user
customizations done in various mode hooks. Similarly, we run
`c-mode-common-hook' also at the very end to leave a place for user
customizations (for example, set `imenu-generic-expression' in
`c-mode-common-hook').
[1] https://www.gnu.org/software/emacs/manual/html_node/elisp/Derived-Modes.html
Re: https://github.com/protocolbuffers/protobuf/issues/7316
Re: https://github.com/protocolbuffers/protobuf/pull/9076
Requiring the legacy ‘cl’ library unconditionally pollutes the namespace.
Instead, require it only when compiling and in known-broken versions.
This is almost the same patch that opoplawski suggested, except that I removed
the test for ‘emacs-repository-version’, which isn’t defined in Emacs 24.3.
