Avoid re-defining the entire Proxy type per-runtime

[kianenigma]

Just thinking out loud: re-writing all of this HIGHLY risky logic every time seems very dangerous to me. Ideally, we would have a base proxy builder that constructs the default NonTransfer, Any, Cancel etc, and we only extend it with the custom ones.

Originally posted by @kianenigma in paritytech/cumulus#1346 (comment)

The answer can be a builder pattern or a macro.

[bkchr]

Writing blockchains isn't easy ;)

Here the question would also be how to find out what is non-transfer in your runtime? How should we do this on the Substrate level?

IMO the current approach is the best approach. It doesn't involve any magic and you have some concrete place where you can look up all of this.

[xlc]

I would actually want to propose to remove NonTransfer. It is just a footgun. We simply don't have it at Acala and just have more fine grained proxy types https://github.com/AcalaNetwork/Acala/blob/e8998a4d323ec17b5d98f7cf6963df4048fcce5e/runtime/common/src/lib.rs#L326-L337

We can setup multiple proxy to achieve union of permissions and I figured that's just the better way.

[kianenigma]

Thinking a bit more about this, I also don't know how to define some opaque concept like NonTransfer or Staking without even knowing the Call type of the runtime 🤷 I was thinking too much in the unicorn world. Closing.