Open Radar

 
Summary:
After inserting Zero-width non-joiner (character U+200C, abbreviated ZWNJ) in the contents of a UITextView, the text positions returned by -[UITextView positionFromPosition:offset:] are shifted.

Steps to Reproduce:
    UITextView *textView = [UITextView new];
    textView.text = @"Auf\u200clage";
    
    NSInteger expectedOffset = 5; // index of 'a'
    UITextPosition *beginning = [textView beginningOfDocument];
    UITextPosition *position = [textView positionFromPosition:beginning offset:expectedOffset];
    NSInteger actualOffset = [textView offsetFromPosition:beginning toPosition:position];
    NSAssert(expectedOffset == actualOffset, @"Actual offset (%d) != Expected offset (%d)", actualOffset, expectedOffset);

Expected Results:
The variable expectedOffset and actualOffset should be equal.

Actual Results:
The variable actualOffset is equal to 6. The assertion fails.

Regression:
The bug occurs only when a ZWNJ character is located between the source position and the character at the provided offset.