For the next Rust upgrade you should be aware of a subtle breaking change - the compiler's internal representation of trait objects has changed. Previously trait objects were represented as a pair of pointer-to-vtable, pointer-to-data. That order has been reveresed to pointer-to-data, pointer-to-vtable (to make it uniform with pointers to slices). If you transmute one of these fat pointers into a struct (or anything else, assuming an ordering) and use its fields, you will get some really weird bugs, possibly nowhere near the actual transmute. A quick look at the Servo code indicates you are doing this. The correct thing to do is to transmute to core::raw::TraitObject.
To help find these evil transmutes, I added a lint (allow by default) - TRANSMUTE_FAT_PTR - which will show you any instances where you transmute to or from any fat pointer. There will be lots of false positives - where you are transmuting to/from just to change the lifetime or mutability or where you're already using the core::raw structs. Let me know if you have any questions about the change. Cheers, Nick _______________________________________________ dev-servo mailing list dev-servo@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-servo
