Proc#binding

static VALUE
proc_binding(VALUE self)
{
    VALUE bindval, binding_self = Qundef;
    rb_binding_t *bind;
    const rb_proc_t *proc;
    const rb_iseq_t *iseq = NULL;
    const struct rb_block *block;
    const rb_env_t *env = NULL;

    GetProcPtr(self, proc);
    block = &proc->block;

    if (proc->is_isolated) rb_raise(rb_eArgError, "Can't create Binding from isolated Proc");

  again:
    switch (vm_block_type(block)) {
      case block_type_iseq:
        iseq = block->as.captured.code.iseq;
        binding_self = block->as.captured.self;
        env = VM_ENV_ENVVAL_PTR(block->as.captured.ep);
        break;
      case block_type_proc:
        GetProcPtr(block->as.proc, proc);
        block = &proc->block;
        goto again;
      case block_type_ifunc:
        {
            const struct vm_ifunc *ifunc = block->as.captured.code.ifunc;
            if (IS_METHOD_PROC_IFUNC(ifunc)) {
                VALUE method = (VALUE)ifunc->data;
                VALUE name = rb_fstring_lit("<empty_iseq>");
                rb_iseq_t *empty;
                binding_self = method_receiver(method);
                iseq = rb_method_iseq(method);
                env = VM_ENV_ENVVAL_PTR(block->as.captured.ep);
                env = env_clone(env, method_cref(method));
                /* set empty iseq */
                empty = rb_iseq_new(NULL, name, name, Qnil, 0, ISEQ_TYPE_TOP);
                RB_OBJ_WRITE(env, &env->iseq, empty);
                break;
            }
        }
        /* FALLTHROUGH */
      case block_type_symbol:
        rb_raise(rb_eArgError, "Can't create Binding from C level Proc");
        UNREACHABLE_RETURN(Qnil);
    }

    bindval = rb_binding_alloc(rb_cBinding);
    GetBindingPtr(bindval, bind);
    RB_OBJ_WRITE(bindval, &bind->block.as.captured.self, binding_self);
    RB_OBJ_WRITE(bindval, &bind->block.as.captured.code.iseq, env->iseq);
    rb_vm_block_ep_update(bindval, &bind->block, env->ep);
    RB_OBJ_WRITTEN(bindval, Qundef, VM_ENV_ENVVAL(env->ep));

    if (iseq) {
        rb_iseq_check(iseq);
        RB_OBJ_WRITE(bindval, &bind->pathobj, ISEQ_BODY(iseq)->location.pathobj);
        bind->first_lineno = ISEQ_BODY(iseq)->location.first_lineno;
    }
    else {
        RB_OBJ_WRITE(bindval, &bind->pathobj,
                     rb_iseq_pathobj_new(rb_fstring_lit("(binding)"), Qnil));
        bind->first_lineno = 1;
    }

    return bindval;
}