Dependency graph for Emacs Lisp files

[Lars Ingebrigtsen <larsi@gnus.org>]

Currently, saying "make" in Emacs doesn't recompile .el files that
depend on other files.  This is generally not a catastrophe, because it
only makes a difference when you change a macro/defsubst (and sometimes
a variable).

But when it does matter, it's annoying that you have to do a "make
bootstrap" to get to a working state.

Making a full dependency graph is difficult, of course, due to all the
various methods files depend on each other (require, load, autoload),
but for the things we're interested in to reduce breakages
(macros/defsubst/defvar), we get 97% of the way there by just looking at
`require'.

So would it make a sense to add something that, along the lines of the
stuff that gathers autoloads, creates a dependency.el file (by just
doing `re-search-forward "(require '"' on all the files), and that would
use this to delete .elc files before compiling the lisp directory, based
on whether something "up" in the dependency chain has changed?

(I'd guess there are some complications here because the resulting graph
can be cyclical, but I don't think that's something that can't be worked
around...)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no