Open Radar

 
Summary:
With FontDescriptorCascadeList being [A, B], after encountering one character that is not supported by font A but supported by font B, UITextView incorrectly continues using font B after that character even if the following characters are perfectly supported by font A and A is before B in FontDescriptorCascadeList.

Notice: the text and fonts are all Chinese, so you'd better have a Chinese engineer to help. The zip file is large because I have to pack in the Chinese font.

In the sample app, font A is "STKaiti-SC-Regular", font B is "STHeitiSC-Light", the character that is supported by B but not A is "⋯", the character that is supported by both A and B is "字".

If rendered correctly, "字" should be the same before and after "⋯".

The 1st line is correctly rendered using Core Text.
The 2nd line is correctly rendered by UILabel.
The 3rd line is incorrectly rendered by UITextView. Notice "字" after "⋯" is not the same as the one before "⋯" because it is incorrectly using font "STHeitiSC-Light" instead of "STKaiti-SC-Regular".

Steps to Reproduce:
1. Launch sample app.
2. Compare the three lines of text.
3. Read the console log to see the incorrect attributed string of UITextView.

Expected Results:
 "字" should be rendered exactly the same before and after "⋯".

Actual Results:
"字" after "⋯" is not rendered the same as the one before "⋯".