Crash-causing bug with custom bittype

[malmaud]

Not sure exactly what's going on, or why I get a stack overflow the first time I try the illegal addition and a crash the second time. This is with Commit 81c84a9 2013-05-22 03:59:37 on OS X.

julia> using Base.Intrinsics

julia> bitstype 8 Mytype <: Unsigned

julia> mytype(x::Integer)=box(Mytype, unbox(Uint8, uint8(x)))
# methods for generic function mytype
mytype(x::Integer) at none:1

julia> mytype(1)+1
ERROR: stack overflow
 in + at promotion.jl:135 (repeats 79998 times)

julia> mytype(1)+1
fish: Job 1, 'julia' terminated by signal SIGILL (Illegal instruction)

[vtjnash]

You haven't defined a + operator for your bitstype, so it falls back on the generic + operations for numbers, which is to promote the two arguments and try again -- except that you haven't defined a promote_rule either, so the result of promotion is a no-op, and the result of trying again is a stack overflow.

There is no guarantee that the memory corruption has not occurred by the time the stack overflow is reported, so it may crash afterwards.

[JeffBezanson]

See also #2815