FWIW I dissected the crashing strings, it's basically all <consonant, virama, consonant, zwnj, vowel> sequences in Telugu, Bengali, Devanagari where the consonant is suffix-joining (ra in Devanagari, jo and ro in Bengali, and all Telugu consonants), the vowel is not Bengali au or o / Telugu ai, and if the second consonant is ra/ro the first one is not also ra/ro (or ro-with-line-through-it).
https://manishearth.github.io/blog/2018/02/15/picking-apart-the-crashing-ios-string/ -Manish On Thu, Feb 15, 2018 at 10:58 AM, Philippe Verdy via Unicode < unicode@unicode.org> wrote: > That's probably not a bug of Unicode but of MacOS/iOS text renderers with > some fonts using advanced composition feature. > > Similar bugs could as well the new advanced features added in Windows or > Android to support multicolored emojis, variable fonts, contextual glyph > transforms, style variants, or more font formats (not just OpenType); the > bug may also be in the graphic renderer (incorrect clipping when drawing > the glyph into the glyph cache, with buffer overflows possibly caused by > incorrectly computed splines), and it could be in the display driver (or in > the hardware accelerator having some limitations on the compelxity of > multipolygons to fill and to antialias), causing some infinite recursion > loop, or too deep recursion exhausting the stack limit; > > Finally the bug could be in the OpenType hinting engine moving some points > outside the clipping area (the math theory may say that such plcement of a > point outside the clipping area may be impossible, but various mathematical > simplifcations and shortcuts are used to simplify or accelerate the > rendering, at the price of some quirks. Even the SVG standard (in constant > evolution) could be affected as well in its implementation. > > There are tons of possible bugs here. > > 2018-02-15 18:21 GMT+01:00 James Kass via Unicode <unicode@unicode.org>: > >> This article: >> https://techcrunch.com/2018/02/15/iphone-text-bomb-ios-mac- >> crash-apple/?ncid=mobilenavtrend >> >> The single Unicode symbol referred to in the article results from a >> string of Telugu characters. The article doesn't list or display the >> characters, so Mac users can visit the above link. A link in one of >> the comments leads to a page which does display the characters. >> > >