I was noticing a lot of white (untouched) code in my XDebug code coverage reports however the method signatures at the top were all green and 100% covered. After some searching I found this thread (don’t bother reading) which led to this thread (scroll fast and occasionally read) which showed some awesome debugging by JoepRoebroek. Bug tracker here.
Ultimately PHP 7 introduced (or maybe “started using differently”) a new constant with bitflags that gets used for ce_flags which happened to collide with the bitflag on a constant that XDebug had been using for years. Luckily the fix was just to shift some bits in XDebug.
