Re: [O] [RFC] Fixing link encoding once and for all

[Neil Jerram]

On Fri, 1 Mar 2019 at 08:14, Nicolas Goaziou <address@hidden> wrote:
>
> Hello,
>
> Neil Jerram <address@hidden> writes:
>
> > Do you mean Windows file names in existing Org files?  I.e. the
> > back-compatibility concern?
> >
> > If so, yes, I confess I didn't think at all about back-compatibility,
> > with my suggestion above.  So perhaps that rules my idea out.
> >
> > If we were starting from scratch, however,
> > - I believe it would technically be fine; i.e. it's a complete and
> > unambiguous encoding
> > - it might be considered awkward for Windows users to have to write
> > c:\\system32\\mydoc.txt instead of c:\system32\mydoc.txt, but I don't
> > know how big a concern that would be.
>
> Thinking a bit more about it, we don't need to escape /all/ square
> brackets, only "]]" and "][" constructs. Therefore, we don't need to
> escape every backslash either.

Agreed.

> The regexp for bracket links could be, in its simple (!) form:
>
>   \[\[\(.*?[^\\]\(?:\\\)*\)\]\(?:\[\([^\000]+?\)\]\)?\]

[then a bit later]
> Small update, in its string form now:
>
>   
> "\\[\\[\\([^\000]*?[^\\]\\(\\\\\\\\\\)*\\)\\]\\(?:\\[\\([^\000]+?\\)\\]\\)?\\]"

Is [^\000] the only (or best) way of saying "any character, including
newlines"?  Could there be actual NUL characters in the document?

More generally I'm not sure I'm fully understanding the regex.  I
_think_ it breaks down like this:

\[\[      # literal [[
\(        # begin group 1
[^\000]*? # non-greedy any characters (0 or more)
[^\]      # something not a backslash
\(        # begin group 2
\\\\      # literal \\
\)*       # end group 2, and allow 0 or more of it
\)        # end group 1
\]        # literal ]
\(        # begin group 3
?         # don't understand
:\[       # literal :[
\(        # begin group 4
[^\000]+? # non-greedy any characters (1 or more)
\)        # end group 4
\]        # literal ]
\)?       # end group 3, and allow 0 or 1 or it
\]        # literal ]

but there's at least a ? that I don't understand, and I'm afraid I'm
not seeing how it's useful.

> Most links would need no change.  I see one notable exception:
> directories in Windows:
>
>   [[c:\system32\\]] for "c:\system32\"

But I guess it would be unusual to write a trailing backslash like that.

> Some further notes:
>
> 1. Macros already use backslashes to escape commas in arguments, so it
>    is at least consistent with this part of Org.
>
> 2. The description part of the link, like most parts of Org, does not
>    use backslash escaping. If needed, we can implement an entity for
>    a square bracket.
>
> 3. There will be some backward compatibility issues. We can add
>    a checker in Org Lint to catch most of those. For example, we could
>    look at URI where every percent is followed only by 25, 5B, and 5D.
>
> WDYT?

If you think it works, I'm happy to defer to your judgement on that!
Although I suggested the idea, I don't know Org nearly well enough to
be sure that I haven't missed problems; but I guess that you would
know that.

Best wishes,
      Neil