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

[Paul Eggert <eggert@cs.ucla.edu>]

On 06/05/2017 09:27 AM, Alan Mackenzie wrote:

> Can you give an example of something which might need two strings?

Suppose the same string is used for both messages and documentation. 
You're proposing %` in the former where ` is in the latter, so we would 
need distinct strings.People cut and paste between messages and doc 
strings, and it's possible there's even code that does this (I haven't 
checked). Using different quoting notations for the two kinds of strings 
will cause confusion and problems.

> 2745 is a good first approximation.

This is being optimistic. It's not just the message and error functions; 
there are others, ranging from general functions like user-error to 
more-specialized functions like icalendar--dmsg.These cannot be found 
merely by a simple text search for function names. A simple albeit 
tedious and somewhat error-prone approach would be to examine every ` 
and ' in every string and character constant (in either C or Elisp) and 
fix those intended for the message function or any of its callers. This 
is the sort of thing that I did when converting for Emacs 25.

> The consequences of surreptitious unwanted translation are so severe

It's not surreptitious: it's documented. And the consequences are not 
severe: they are a minor change to strings intended for human 
consumption, where humans can easily recover from unwanted translation, 
and where humans who don't want translation can easily turn it off.

As I understand it, you're proposing making hundreds or thousands of 
changes like this:

          (error "Can't find `%s' in %s" thing where)))
  =>      (error "Can%'t find %`%s%' in %s" thing where)))

These changes will adversely affect code readability, and this will have 
a maintenance cost in the long run -- not just to whoever makes the 
hundreds or thousands of changes, but to everybody who has to read the 
code afterwards.It's not at all clear that this cost is greater than the 
benefit of fixing some of the minor problems that you're objecting to.

> _Anybody_ who's used `message' knows

Perhaps I should introduce you to my students someday. I teach them 
elements of Emacs and I assure you that some of them do not know. 
Although I readily concede that more people know about % than ` or ', 
this doesn't alter the fact that it causes problems to support special 
characters of any sort in the message function. Elisp code needed to use 
(message "%s" STR) even before the change you're objecting to, and it'd 
still need (message "%s" STR) even if the change were reverted.

> It is not merely annoying, it is hideously irregular. Having to write
> (message "%s" (format "...." arg1 arg2 ....)) screams out "we didn't
> think this through properly".

Yes, and that's just as true for % as it is for ` and '. In hindsight, 
the message function should have had a better API. Hindsight is 
wonderful....