Move `Block`, `NodeBlock` and `UncheckedExtrinsic` to `frame_system`, instead `construct_runtime`

[kianenigma]

I came across this in my effort to make the simplest FRAME runtime and pallet, for the new tutorials in https://github.com/paritytech/polkadot-sdk-docs/.

The observation is that construct_runtime, and the need to define type UncheckedExtrinsic and type Block is quite noisy. At best, in a tutorial, you should say: "shuuush... just ignore these for now", which sucks.

type Extrinsic = MockUncheckedExtrinsic<Runtime>;
type Block = MockBlock<Runtime>;

frame_support::construct_runtime!(
	pub struct Runtime
	where
		Block = Block,
		NodeBlock = Block,
		UncheckedExtrinsic = Extrinsic,
	{
		System: frame_system,
		Currency: pallet,
	}
);

Ideally, I want this to just be:

frame_support::construct_runtime!(
	pub struct Runtime {
		System: frame_system,
		Currency: pallet_currency,
	}
);

And I am inclined to think that it is possible.

The fact that construct_runtime needs to know these types is unavoidable. But, can't it get these from frame_system::Config? I think we already have a pretty hard requirement for the frame_system to exist, and exist with the exact crate name frame-system. So it should be possible for construct_runtime to get these types as <#frame_system::Pallet as #frame_system::Config>::Block.

Even further, I think with #13454 we can actually have these have their defaults be set to the things that are in frame_system::mocking:: and free the whole universe from needing to define them at all in 95% of tests.

Needs to be verified. Would love to hear @ggwpez and @bkchr's opinion.

If deemed feasible, suggest @gupnik to take it over.

[bkchr]

I think the block types can be removed when we have the sp-api refactorings implemented.

For the extrinsic we first should check where we currently require it.

[kianenigma]

Let's assume the worse case, that we need both. Can't we move them to type Block, type NodeBlock and type Extrinsic to frame_system::Config, and instruct construct_runtime to read it from there?

I think the block types can be removed when we have the sp-api refactorings implemented.

do you have an issue pr PR?

[gupnik]

I will try to create a prototype to see if this could work.

[bkchr]

do you have an issue pr PR?

paritytech/polkadot-sdk#27

[kianenigma]

I will try to create a prototype to see if this could work.

I would suggest keeping it based on DefaultConfig PR and seeing of you can provide defaults for it as well.