Broken Code Highlighting in KDevelop

[David Redondo]

Hi,

recently files began to start losing their highlighting when editing in 
KDevelop. Symptoms are as follows:
 - After inserting a new line anywhere in a document, everything below the new  
line will lose its highlighting
 - When writing in the new line, the new code is highlighted correctly
 - Removing the new line restores correct highlighting in the rest of the file

Yesterday after an older KDevelop showed the same behavior, I bisected
fde333c87353e7c7424c7bce5cbc2f984bc868c1 in KTextEditor to have introduced 
this. Nothing there immediately appears to me to cause this. 
With the power of debug statements I confirmed that KDevelop reaches the 
"applyHighlighting" function (https://invent.kde.org/kdevelop/kdevelop/-/blob/
master/kdevplatform/language/highlighting/codehighlighting.cpp#L519) and is 
not hitting any of the early returns. Then follows some range logic and I did 
see that the setAttribute calls at the end are also happening.

I'm not sure if the KTextEditor change surfaced a bug in KDevelop (somewhere 
in the range manipulation?) or if something in KTextEditor is not working 
correctly.

Best Regards,
David