ARGS constant doesn't get set correctly anymore

[StefanKarpinski]

$ julia -e 'println(ARGS)'
Array(Any,(0,))
$ julia -e 'println(ARGS)' foo bar
Array(Any,(0,))

[StefanKarpinski]

@JeffBezanson: I can't figure out why this doesn't work. The code is here and appears in the debugger to be doing the right things:

jl_array_t *args = jl_alloc_cell_1d(argc);
jl_set_const(jl_system_module, jl_symbol("ARGS"), (jl_value_t*)args);
int i;
for (i=0; i < argc; i++) {
    jl_arrayset(args, i, (jl_value_t*)jl_cstr_to_string(argv[i]));
}

Stepping through it, everything looks fine, but then when I try to access ARGS as above from julia, I get a zero-element cell array instead of the properly initialized ARGS. Am I doing something wrong here? Did the usage of one of these functions change? Or is this a weird interaction with the snapshot restoration process?

[StefanKarpinski]

Right after that, setting the JULIA_HOME constant works:

jl_set_const(jl_system_module, jl_symbol("JULIA_HOME"),
             jl_cstr_to_string(julia_home));

So that set of functions still appears to be working as expected.

[JeffBezanson]

D'oh, it must be because the system image saves the value, and it's a constant so it won't let you overwrite the value. I guess we should allow overwriting constants from the C API.

[StefanKarpinski]

How does this even get set in the image? Ideally, the constant should get created only after loading the image. Likewise, JULIA_HOME should get reset each time. An alternative would be to make these not be constants at all. Also, I added JULIA_HOME before we has access to the EnvHash singleton so maybe that should just be gone.

[JeffBezanson]

Because it gets set every time julia starts, and the system image saves the entire state. So the system image contains the values as they were when the image was saved. They don't have to be constants, you can change that if you want.
JULIA_HOME is not always an environment variable. It's set using the proc filesystem to find where julia actually is. I don't see the advantage of typing ENV["JULIA_HOME"] instead of just the variable name.

[StefanKarpinski]

No, I guess that's fair. And sometimes ENV["JULIA_HOME"] and JULIA_HOME won't match. If they're not constants would that solve the issue?

[JeffBezanson]

Yeah, just use jl_set_global instead of jl_set_const