Correct Path to Emacs C Sources after Installation

[Stephen J. Turnbull]

Alexander Shukaev writes:

 > For the installation phase we add the *optional*
 > "--install-sources" flag which would trigger copying of C sources
 > under "${etcdir}/../src" (which in fact is
 > "<datadir>/emacs/VERSION/src"). We also apply the attached patch.

A technical comment:  Why not simply set source-directory in
site-start (or default.el if Emacs doesn't have site-start)?

Where do you add the optional flag?  In configure?  If so, you're
likely to overwrite the sources on future installations due to caching
of options in config.status, which may or may not be the right thing
(in particular, it could confuse make).  Or would it be a make target?

Even if you did install, the sources won't be guaranteed to be there
(although they're more likely to exist).  I see one usability problem
with the location you chose: for most users, it's likely to be
read-only, and if not, you have a race condition if different users
have access.

A suggestion: add an option to install not a copy of the C sources,
but rather a clone of the repo.  Note that if the complete version
string includes the revid, you can always recover the exact sources
used to build the executable.