Thanks Tim! Pretty nice answer that I can learn from! Thanks for your time.

I definitely knew my Regex was broken, yet I was surprised the interpreter/library didn't gave up/error after some(several million) steps.

Some other language seems to just assume there will be no match (Source: some play on https://regex101.com/), and I don't think this is a valid approach.

Should there be a WARNing logged on a defined soft-limit?

I know this is low-level "re" library, and your point is pretty valid about the fact the lib should be doing what it's told to do. 
I was mostly looking for opinion about WARNs on soft limits and maybe errors on a hard-limit to debug/avoid this kind of false-hang situation.

Feel free to close/wont-fix/not-a-bug this issue! And thanks again for your kind answer to my initial issue!