Bug 21116 – onArrayCastError is horribly unsafe

If you cast an array incorrectly, you get a blank message, or an incomplete message, or you may get junk. That's because onArrayCastError (which is @trusted) uses a stack buffer for its message, and then throws an assert error with the reference to that message! Not only that, but it also incorrectly converts numbers into stack strings, and then references those in an array after they are gone. I think there are only 2 valid ways out -- 1: allocate the string in the static data segment, or 2: allocate it on the C heap. I'm not sure which one to do. Both have drawbacks. Obviously, we can't use the GC as this is a core language feature. Using the C heap isn't great either, but is a reasonable solution. Using a static data segment one has to do purity acrobatics. And it may be really difficult to only allocate the segment if an array cast occurs. I'm leaning towards doing a C heap allocation.

It also assumes that assert() accepts null-terminated strings. On windows, it does not, so garbage gets printed fairly reliably there.

@schveiguy created dlang/druntime pull request #3185 "Fix issue 21116 - Do not squirrel stack pointers away in AssertErrors." fixing this issue: - Fix issue 21116 - Do not squirrel stack pointers away in AssertErrors. https://github.com/dlang/druntime/pull/3185

dlang/druntime pull request #3185 "Fix issue 21116 - Do not squirrel stack pointers away in AssertErrors." was merged into master: - d48c3b7d8475a18d3457e7a18929b104f906a82e by Steven Schveighoffer: Fix issue 21116 - Do not squirrel stack pointers away in AssertErrors. https://github.com/dlang/druntime/pull/3185