bug#60954: 29.0.60; ERC 5.4.1: loading ERC clobbers customizations to erc-mode-hook

[J.P.]

Tags: patch

To reproduce:

  1. Put the following in /tmp/test/init.el
  
       (custom-set-variables
        '(erc-mode-hook '(erc-imenu-setup visual-line-mode)))

     which is exactly what you'd get by doing

       M-x customize-group RET erc-hooks RET

     and adding a `visual-line-mode' item to `erc-mode-hook'.

  2. Run

       emacs --no-site-file --init-directory=/tmp/test

  3. If you do a

       C-h v erc-mode-hook RET

     which loads `erc' behind the scenes, the hook's value will be

       (erc-imenu-setup)

     Note the missing `visual-line-mode'.


Superficially, this is a regression stemming from 

  bug#56340: 29.0.50; [PATCH] Don't ask people to order requires.

which became

   commit c2d657e7c4fd9685591f2120007eabf78745919d
   Author: Dick R. Chiang <dick.r.chiang@gmail.com>
   Date:   Fri Jul 1 11:06:51 2022 -0400

   Move ERC's core dependencies to separate file

But amid all that rearranging, a subtle and pernicious headache long ago
swept under the rug happened to resurface [1].

I see two basic avenues of attack here. The first is a pretty safe
stopgap and the second a slightly riskier comprehensive approach that
should have been on the books the moment that bug was closed:

  hack: partially revert a tiny hunk from the commit above

  fix:  don't require goodies at all and instead update the module
        mapping data and add all necessary autoloads and forward
        declarations

Implementations of both are attached. (I didn't bother updating the
required Compat version in the second patch, but that'd also need to
accompany the change set.) For now, I propose we take the shorter route
but with an eye toward revisiting the issue soon after the next (ERC)
release. If anyone has an opinion here, now would be the time to speak
up.

Thanks.

P.S. This bug owes its existence to Libera user jrm, who kindly brought
it to our attention earlier today.


[1] Some related background. For ages, `erc-goodies' was `require'd by
    erc.el at the very end of that file, likely in order to sidestep the
    manual module-to-feature mapping needed by `erc-update-modules' for
    outliers whose names don't match their features (arguably justified
    for smaller, miscellaneous modules). A secondary benefit and
    possible motivating factor was that various commands from goodies
    could feature in `erc-mode-map' without being autoloaded. However,
    additional liberties were eventually taken until erc-goodies.el
    became a de facto addendum to erc.el.



In GNU Emacs 29.0.60 (build 1, x86_64-pc-linux-gnu, GTK+ Version
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Repository revision: 7b7b2b95138e691f1b155060b91a8998e3905651
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0001-Don-t-load-erc-goodies-atop-erc.el.patch
Description: Text Data

0002-5.6-Copy-over-upstream-Compat-macros-to-erc-compat.patch
Description: Text Data

0003-5.6-Don-t-require-erc-goodies-in-erc.el.patch
Description: Text Data