bug#34215: 27.0.50; Provide elisp access to Chinese pinyin-to-character mapping

[Eli Zaretskii <eliz@gnu.org>]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Date: Sun, 27 Jan 2019 10:02:48 -0800
> 
> >> I'm not sure this use of `source-directory' is particularly robust, but
> >> I don't know how else to handle it.
> >
> > source-directory might not exist in a given installation.
> >
> > Maybe we should have the data copied into that separate file I
> > mentioned above.
> 
> I can imagine a few ways of doing that:
> 
> 1. Just manually copy the data into a new file and add it to the repo
>    (pinyin.map hasn't been updated in years).
> 2. Do the copy at build time. I'm not quite sure where that function
>    would live, or how it would get called.
> 3. Use an `eval-and-compile' form as in the patch I provided. Is working
>    back from `load-file-name' more reliable than using
>    `source-directory'?

2 is what I had in mind.  I don't think it matters where the code
lives, it's small enough to not matter.  It would be called like the
various *-convert functions we invoke at build time to build the
dictionaries needed for CJK input methods, see the files in the leim/
directory.

> Autoloading a variable seems to copy the value of the variable into the
> loaddefs file, so there's no point to that. I figure we can just ask
> people who want this value to require the library.

Right.

> PS: pinyin.map is ancient and is missing a lot of good correspondences.
> Google's pinyin input method uses a much larger map, licensed with
> Apache v2.0. This[1] seems to indicate that Apache 2.0 is okay for Gnu
> projects, maybe we could consider switching to that map?

Maybe.  Unfortunately, I don't know enough about these input methods
to tell whether replacing the file is a good idea.  I wonder who can
we ask about this.