Re: [Emacs-diffs] master c4151eb: Improve the optional translation of quotes

[Dmitry Gutov]

On 06/24/2015 08:24 AM, Paul Eggert wrote:

> As I mentioned earlier I never fully understood the font-lock proposal.
> I could not easily decipher most of the abovementioned message.

Asking questions might help. I can't help but feel frustrated that you 
haven't made an informed decision. See the bottom of this email for the 
patch against f743819 (which was the version in master at the time). It 
only adds one line, the one I've mentioned in that message.

I'm not sure what more to explain, but the undesirable effect you've 
seen was due to 
http://www.gnu.org/software/emacs/manual/html_node/elisp/Syntactic-Font-Lock.html

> Luckily, though, the abovementioned message briefly mentioned not using
> font-locking and said of it "...but indeed, this approach could be the
> simpler one." -- an assessmeent that seemed sound to me -- and so I took
> the simpler approach.

I did say that, tentatively, and I've changed my mind since.

- Using font-lock will allow to change the output significantly in the 
future, without breaking the substitute-command-keys API.

- This functionality is closely related to linkification of identifiers 
between the quotes, also performed in Lisp (see the usages of 
help-xref-symbol-regexp). If substitute-command-keys handles escapes, 
help-xref-symbol-regexp (and the function using it) don't know whether a 
given quote was escaped or not). Especially if the source file can 
contain curly quotes, and substitute-command-keys also translates into them.

- "too tempting to implement complicated heuristics that would have been 
a pain to document" is not a good argument not to do something in a 
high-level language.

Now, there are still problems with that patch:

- It doesn't handle escaping either. Someone just needs to pick the 
escaping syntax, and we can handle it in Lisp just as well as in C. Why 
did we decide that "\\" isn't good enough?

- Like you said: "describe-variable should curve the quotes in the doc 
string, but not in the contents of the variable". The code that prints 
the value will need to add some text property to it ("verbatim"? 
"font-lock-ignore"?), and the font-lock rule can look it up and skip 
those regions. Nothing too hard.