offer to save customizations on exit?

[Drew Adams]

Note: This message discusses a possible new feature, for after the release.
Any followups can be off-list.

Analogy A~B:

A. You visit several files, and modify some of their buffers. You hit `C-x
C-c'. Emacs asks whether you want to first save each or all of the modified
files before exiting. You can reply to save all, save none, or save specific
files.

B. You customize several user options but you don't save the changes. You
hit `C-x C-c'. -- Ooops! your changes are gone, without warning. --

The analogy breaks down here. Emacs should ask you whether you want to first
save the changed-but-unsaved options.

You should be able to say "Yes to All", "No to All", or "Yes" or "No" to
each individual option. You should also be able to say "Visit" to go to a
Customize buffer to examine each option (see its current value, init value,
doc etc.).

IOW, a set of buffers visiting files is like an Emacs session "visiting"
your custom-file (.emacs). When you request to quit Emacs, you should have a
chance to act on any changes that have not yet been saved.

The analogy holds also wrt settings you change and then change back: If you
set an option and then set it back to the previous value, this is not
recognized as a no-op - just as for buffer changes without saving. If you do
`erase-customization', however, it is as if no changes had been made - just
as for undoing buffer changes.

Other opinions?

 - Drew

P.S. The code already exists to implement both checking for unsaved option
changes and visiting ("Visit") a customize buffer with those options - see
`customize-customized'. (The list of customized-but-not-saved options to be
visited could be first pruned of those for which the user has said "No".)