[Webkit-unassigned] [Bug 231606] ASSERT hit in surrogatePairAwareIndex and surrogatePairAwareStart lambdas for text with unpaired surrogates

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=231606

--- Comment #15 from Darin Adler <darin at apple.com> ---
Comment on attachment 440982
  --> https://bugs.webkit.org/attachment.cgi?id=440982
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=440982&action=review

>>>> Source/WebCore/layout/formattingContexts/inline/text/TextUtil.cpp:155
>>>>  
>>> 
>>> It would be:
>>> 
>>>     auto right = std::min<unsigned>(left + offset, (startPosition + length - 1));
>>>     U16_SET_CP_LIMIT(text, 0, right, text.length());
>>> 
>>>     auto middle = surrogatePairAwareIndex((left + right) / 2);
>>>     U16_SET_CP_LIMIT(text, 0, middle, text.length());
>> 
>> Thank you, I will try this! Although I just notice that currently, surrogatePairAwareIndex returns the index at trail whereas U16_SET_CP_LIMIT returns the index past it:
>> 
>> #define U16_SET_CP_LIMIT(s, start, i, length) UPRV_BLOCK_MACRO_BEGIN { \
>>     if((start)<(i) && ((i)<(length) || (length)<0) && U16_IS_LEAD((s)[(i)-1]) && U16_IS_TRAIL((s)[i])) { \
>>         ++(i); \
>>     } \
>> } UPRV_BLOCK_MACRO_END
> 
> Oh, OK, good point. So my code is wrong. It would be more like this:
> 
>     auto right = std::min<unsigned>(left + offset + 1, startPosition + length);
>     U16_SET_CP_LIMIT(text, 0, right, text.length());
>     --right;

And perhaps then could change the logic to get rid of the need for the "--right".

Maybe a waste of time, but I do think that using the U16 macros is still a little easier to get correct than writing our own code.

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