Re: [Emacs-diffs] master 9ce1d38: Use curved quotes in core elisp diagnostics

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

Dmitry Gutov wrote:

> An ambiguity in `format' can cause an unexpected error due to a
> program, say, being unable to open a file.

Yes, although that's a longstanding problem: it's not something that the recent 
quoting-style changes have introduced, and it's not something that we really 
need to address now.

That being said, we could attack the problem somewhat by having %qs not only 
quote its output, but also insert backslashes in front of each troublesome 
character (which should include the characters in the string "\n\\\"'‘’“”", 
say).  This would work only in output contexts where backslash escapes make 
sense, but that's reasonably common and anyway the output would be unambiguous, 
which is better than what we have now.

A possible downside of changing %q's behavior in this way is that it'll double 
backslashes in file names, and maybe MS-Windows users wouldn't like that.  For 
example, if NAME is the file name ‘C:\Documents and 
Settings\Eggert\Example.png’, then:

    (error "Cannot find image file %qs" name)

would output:

    Cannot find image file ‘C:\\Documents and Settings\\Eggert\\Example.png’

and the doubled backslashes could be a bit disconcerting.