bug#23425: master branch: `message' wrongly corrupts ' to curly quote.

[Alan Mackenzie]

[ Message posted to emacs-devel@gnu.org, with Reply-To: set. ]

Hello, Paul.

On Fri, Jun 02, 2017 at 14:47:42 -0700, Paul Eggert wrote:
> On 06/02/2017 02:02 PM, Alan Mackenzie wrote:
> > How about transferring this discussion to emacs-devel, so that more
> > people would be able to see it.

> We had that discussion there already, and I doubt whether it’d be 
> worthwhile to repeat it. Of course you're free to take it there again if 
> you like.

The previous discussion was abruptly cut short, without reaching a
conclusion, with a "we're too close to a release to change anything
now".  This came with the implicit understanding the discussion could be
countinued after the release.

> > The default behaviour has been changed already, and that change has
> > caused problems and will cause further problems.

> I expect that most of the practical problems have been shaken out 
> already with the changes published in Emacs 25.1 last year, so that most 
> of this cost has already been paid.

They have not.  We have moved from a state where everybody knew what
`message' did (in Emacs 24), to one with wild special characters which
only apply sometimes, and necessitate crazy prolix formulations to work
around unwanted translations of quote characters.

`message' is currently broken.

Introducing quote translation has introduced a burden on all users of
`message'.  Seeing how poisonous and insidious this translation can be,
it makes sense to shift this burden over to the use cases where the
programmers need quote translation, and hence will be aware of it.

> > I propose restoring the default to what it was in Emacs 24.  For
> > simplicity's sake, only % should be special, and for translating quotes
> > we could introduce %' and %`, such that quote translation happens only
> > when a %' or %` is present.

> That kind of approach was proposed way back when. It doesn’t address 
> quotes in doc strings, though.

Of course it doesn't.  Doc strings have their own peculiar quoting
mechanisms which are disjoint from those of `message'.

> More generally, a problem with this sort of approach is that although
> it simplifies ‘message’ (obviously), this is at the price of
> complicating everything else.

What is the "everything else" that gets thus complicated?  I don't see
anything else getting more complicated.

> I estimate we’d need to change 10,000 lines of Emacs source code to
> make that change to ‘message’. (This is a just a quick estimate based
> on ‘grep '".*`.*"'’.) The resulting source code would typically be a
> bit harder to read than it is now.

I think this estimate is way over the mark.  There are around 17,000
occurrances of "message" in our Lisp sources, and probably a few in our
C sources.  Only (some of) those containing the quote characters in the
format string would need amendment.  These will comprise a tiny portion
of these ~17,000, and can be found easily enough with a script.

-- 
Alan Mackenzie (Nuremberg, Germany).