Is there a way to get the stacktrace from an error object?

New to Julia
1

I have an object with type MethodError. I want to print the stacktrace (ie, backtrace) to see where it occurred. How do I do that? I see a method backtrace but it doesn’t take an argument.

propertynames(err) reveals only one property: :msg.

2

not really, IIRC the Error object only contains error (what function, what world age, what argument etc.), not the backtrace

3

Okay. I’m trying to embed Julia. If I run a file of Julia code, from C code, and I get an error back (from jl_exception_occured), it seems I have no way to print the stack trace or useful source location info.

4

Depending on the precise situation, maybe rethrow can help you out. But yeah the error object doesn’t contain the full stacktrace

5

Aside from a full stacktrace, does it contain any source location info at all? It seems, no. And if that’s the case, I don’t see how you can embed a non-trivial amount of Julia code.

6

Julia will scan the current execution stack when encountering errors. The source location and other debug information are allocated and set up with the stack frame. It seems that there’s a experimental function Base.catch_stack which is suitable for your task. But you still need to wrap your code in a try-catch-block to provide an exception handle.

7

Do you mean wrap in try/catch in C code? Something like this? (not working)

JL_TRY {
    jl_value_t *result = jl_eval_string(code);
    // result in null, catch block does not run
}
JL_CATCH {
    jl_printf((JL_STREAM*)STDERR_FILENO, "ERROR:\n");
    jl_static_show((JL_STREAM*)STDERR_FILENO, jl_current_exception());
    jl_printf((JL_STREAM*)STDERR_FILENO, "\n");
    jl_print_backtrace(); // backtrace(); // written to STDERR_FILENO
}

I copied that use of the JL_TRY and JL_CATCH macros from Julia’s C code.

8

I guess jl_eval_string already has a try-catch-block and simply ignores the error for you, so you need to dig into jl_eval_string further to find out the actual function.

9 
JL_DLLEXPORT jl_value_t *jl_eval_string(const char *str)
{
    jl_value_t *r;
    JL_TRY {
        const char filename[] = "none";
        jl_value_t *ast = jl_parse_all(str, strlen(str),
                filename, strlen(filename));
        JL_GC_PUSH1(&ast);
        r = jl_toplevel_eval_in(jl_main_module, ast);
        JL_GC_POP();
        jl_exception_clear();
    }
    JL_CATCH {
        jl_current_task->ptls->previous_exception = jl_current_exception();
        r = NULL;
    }
    return r;
}

This is the definition of jl_eval_string. Simply duplicating this function and adding your exception handling code to JL_CATCH should be fine.

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