How to figure out why proc is not GC-safe? And is there a way to force Nim to ignore that?

[alexeypetrushin]

I'm trying to run some proc with threads and get this error:
    
    
    crawl.nim(9, 6) Error: 'run_crawler' is not GC-safe as it calls 'build_jobs'
    
    
    Run

The problem is that there are lots of code that it uses. In this case it 
complains about the `build_jobs` proc, but it in itself uses lots of other 
procs.

Is there a way to discover what exactly in dependencies of `build_jobs` cause 
the GC-safe problem?

And is it possible to force Nim to run the code anyway?