Segfault when accessing uninitialized Nullable field

[johnmyleswhite]

johnmylesw-mbp1:julia-0.4 johnmyleswhite$ julia-0.4
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "help()" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.4.0-dev+5317 (2015-06-11 15:18 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit b3a7342* (0 days old master)
|__/                   |  x86_64-apple-darwin14.3.0

julia> function Base.(:+){S1, S2}(x::Nullable{S1}, y::Nullable{S2})
           resval = Base.(:+)(x.value, y.value)
           T = typeof(resval)
           if x.isnull || y.isnull
               return Nullable{T}()
           else
               return Nullable{T}(resval)
           end
       end
+ (generic function with 140 methods)

julia> Nullable(1) + Nullable()

signal (11): Segmentation fault: 11
jl_method_table_assoc_exact at /Users/johnmyleswhite/julia-0.4/src/gf.c:261
jl_apply_generic at /Users/johnmyleswhite/julia-0.4/src/gf.c:1604
+ at none:2
jlcall_+_21298 at  (unknown line)
jl_apply at /Users/johnmyleswhite/julia-0.4/src/gf.c:1632
jl_apply at /Users/johnmyleswhite/julia-0.4/src/interpreter.c:55
eval at /Users/johnmyleswhite/julia-0.4/src/interpreter.c:212
jl_toplevel_eval_flex at /Users/johnmyleswhite/julia-0.4/src/toplevel.c:523
jl_toplevel_eval_in at /Users/johnmyleswhite/julia-0.4/src/builtins.c:539
eval_user_input at REPL.jl:62
jlcall_eval_user_input_21269 at  (unknown line)
anonymous at task.jl:91
jl_apply at /Users/johnmyleswhite/julia-0.4/src/task.c:234

Segmentation fault: 11
johnmylesw-mbp1:julia-0.4 johnmyleswhite$ 

Shows up on master right now.

[mbauman]

Nullable() defaults to having an element of type Union(), which is probably where this trouble is stemming from. In fact, on a recent build with LLVM-svn, I can't even print Nullable(), which is even more concerning:

julia> Nullable()
Assertion failed: (jl_is_datatype(ty)), function ghostValue, file codegen.cpp, line 2796.

signal (6): Abort trap: 6
__pthread_kill at /usr/lib/system/libsystem_kernel.dylib (unknown line)
Abort trap: 6

[johnmyleswhite]

Yup, the problem does seem to stem from the representation of Union(): the same code won't segfault with a Nullable{Int}() or other sane input.

[yuyichao]

Looks like the codegen pushes a single value (the Int) on in the argument array and then told jl_apply_generic that there are two argument.

[johnmyleswhite]

Thanks, Jeff!