bug#10130: 24.0.91; eldoc error DOC-24.0.91.1 not found

[Eli Zaretskii <eliz@gnu.org>]

> From: Thierry Volpiatto <thierry.volpiatto@gmail.com>
> Date: Thu, 24 Nov 2011 22:09:59 +0100
> 
> --8<---------------cut here---------------start------------->8---
> eldoc error: (error Cannot open doc string file
> "/usr/local/share/emacs/24.0.91/etc/DOC-24.0.91.1")
> --8<---------------cut here---------------end--------------->8---
> 
> I have in ../etc a file named DOC-24.0.91.3
> Creating a symlink to DOC-24.0.91.1 workaround the problem.
> 
> What is this file for exactly?

When you build Emacs, the build creates 2 hard links to the same
binary: `emacs' and `emacs-NN.MM.XX.YY'.  It does the same with the
DOC file, because, as Glenn explained, each build should have its
matching DOC file.  Building another binary will break the link of
`emacs' to the binary and link it to the newer binary, and will also
make another hard link of the form `emacs-NN.MM.XX.YY' by incrementing
the YY part.

After rebuilding Emacs several times, you will have several
`emacs-NN.MM.XX.YY' binaries and `emacs' that is linked to one of
them, normally the one with the largest YY part.  The same is true for
the DOC file.

This allows you to run previously built binaries by invoking one of
the `emacs-NN.MM.XX.YY' programs, and the DOC files that go with each
one of them will then be available for Emacs to use.

IOW, this is a feature (and quite a useful one, e.g., when you are
faced with a recently introduced bug and want to know which build
introduced it).