[FFmpeg-trac] #11096(undetermined:new): Chaotic escaping rules

[FFmpeg]

#11096: Chaotic escaping rules
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             Reporter:  ManDay       |                    Owner:  (none)
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  git-master   |               Resolution:
             Keywords:               |               Blocked By:
  filter_complex expression          |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by ManDay):

 I don't see a general (conceptual) issue. Could you elaborate what you
 mean (I'm not a CStist and "Reverse Solidus Toothbrush" didn't bring up
 any results).

 In principle, I think escaping and quoting follows a simple pattern, which
 is unrecognizable in FFMPEG:

 Starting from the "top" (whole data), **recursively** define parsers which
 operate on the input and, by their respective syntactic elements,
 decompose the data into semantically related blocks, which are fed into
 "lower" parsers. These blocks are atomic/opaque to the parser at this
 level.
 To prevent data from being (mis)interpreted as syntactic elements, two
 special syntactic elements are defined:
   - Quotes (prevent interpretation in their range)
   - Escapes (prevent interpretation immediately after)

 In this case, one possibility to split the parsing could be:

 At the "top" we have the //filter-complex// parser with escape `\` and
 quote `'` which parses `drawtext=text='%{e:if(1,\'a\',\'b\')}'` into
 blocks `drawtext` `text` `%{e:if(1,'a','b')}`. By their semantics,
 `drawtext` is used to create a filter to which the arguments of type
 `pair[]`, here {(`text`,`%{e:if(1,'a','b')}`)} are handed over.

 At a lower level we have the //drawtext// parser for //parameter names//
 which parses `text` (trivial) and the //drawtext text// parser which
 parses `%{e:if(1,'a','b')}`. The //drawtext text// parser uses escape `\`
 and no quotes (afaik). It yields the blocks: `e` and `if(1,'a','b')`.

 At the lowest level we have the //expression// parser with escape `\` and
 quote `'`.
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Ticket URL: <https://trac.ffmpeg.org/ticket/11096#comment:3>
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