Add optional importing of variables/procedures

[phobos2077]

Need some ways to check if variable was exported before fetching/storing (and possibly crashing the script). This should allow for global scripts to communicate without hard requirements.

Concrete motivation for this: my damage mod script needs to read/write some data for other global script to use. But if these external vars doesn't exist, it can work normally as a stand-alone damage mod, because it doesn't depend on them.

[phobos2077]

So there's 2 ways to approach this (at least):

1. Add new opcode/metarule to check if given exported var exists:

import variable super_var;
//...
value := super_var
   if external_var_exists(@super_var) // can use stringify operator here to not confuse ssl optimizer
   else 0;

2. Change vanilla op_fetch_external to just print error and return 0 but continue script. op_store_external similarly can just print error and continue. Not sure how "correct" this is but it will solve the main issue. You can check against 0 to see if some variable was set or not.

@dekrus thoughts?

[dekrus]

I believe that modifying the existing op_fetch_external and op_store_external functions is the best option. This approach looks fairly simple to implement and ensures backward compatibility, so we won’t disrupt any existing scripts, if there are any. Although there is a risk of silent failures, users can refer to the logs for troubleshooting

P.S.
Sorry for the late response if anyone was waiting for it. I didn’t realize I was mentioned in the thread...