Re: [PATCH v2 0/2] mingw: handle absolute paths in expand_user_path()

"Johannes Schindelin via GitGitGadget" [off-list ref]
writes:

In Git for Windows, we ran with a patch "in production" for quite a while
where paths starting with a slash (i.e. looking like Unix paths, not like
Windows paths) were interpreted as being relative to the runtime prefix,
when expanded via expand_user_path().

This was sent to the Git mailing list as a discussion starter, and it was
pointed out that this is neither portable nor unambiguous.

After the dust settled, I thought about the presented ideas for a while
(quite a while...), and ended up with the following: any path starting with
<RUNTIME-PREFIX>/ is expanded. This is ambiguous because it could be a valid
path. But then, it is unlikely, and if someone really wants to specify such
a path, it is easy to slap a ./ in front and they're done.

I just went back to briefly scan the discussion in late 2018.

I think the rough consensus back then was that 

 * It indeed is a problem that there is no syntax for users of
   "relocatable Git" to use to point at things that come as part of
   the "relocatable Git" package.

 * A change to expand_user_path() would be too broad, it makes sense
   for this feature to be in git_config_pathname();

 * We need to get the syntax right.

As to the last item, there were a handful of choices raised:

 - Use "~~"--the downside is that this is not extensible.  Use
   "~runtime-prefix/" would be a better choice (the likelyhood of
   <RUNTIME-PREFIX>, $RUNTIME_PREFIX, and any other random choice
   happens to be used as a valid directory name is just as slim as
   the likelyhood of "runtime-prefix" used as a valid username).

 - "$RUNTIME_PREFIX" to make it read like a variable---the downside
   was that it looked TOO MUCH like a variable and risked user
   confusion (e.g. it may be upsetting that "$HOME/.gitconfig" is
   not expanded like "~/.gitconfig" is).

 - %(RUNTIME-PREFIX) to make it similar to how Git replaces various
   tokens that are understood only in the context of Git.

 - <RUNTIME-PREFIX>---the downside is that this is an unnecessary
   new syntax we do not have to introduce.  If <RUNTIME-PREFIX> is
   unlikely to be used as a valid directory name, %(RUNTIME-PREFIX)
   is just as unlikely.

There might have been other ideas floated back then.  I have to say
that the one you chose in this round is the least favourite of mine,
and if you consulted me privately before redoing this round, I would
probably have said %(RUNTIME_PREFIX) would make the most sense among
the candidates.

Thanks.