Construct Runtime v2 (#1378)

Moved from https://github.com/paritytech/substrate/pull/14788

----

Fixes https://github.com/paritytech/polkadot-sdk/issues/232

This PR introduces outer-macro approach for `construct_runtime` as
discussed in the linked issue. It looks like the following:
```rust
#[frame_support::runtime]
mod runtime {
	#[runtime::runtime]
        #[runtime::derive(
		RuntimeCall,
		RuntimeEvent,
		RuntimeError,
		RuntimeOrigin,
		RuntimeFreezeReason,
		RuntimeHoldReason,
		RuntimeSlashReason,
		RuntimeLockId,
                RuntimeTask,
	)]
	pub struct Runtime;

	#[runtime::pallet_index(0)]
	pub type System = frame_system;

	#[runtime::pallet_index(1)]
	pub type Timestamp = pallet_timestamp;

	#[runtime::pallet_index(2)]
	pub type Aura = pallet_aura;

	#[runtime::pallet_index(3)]
	pub type Grandpa = pallet_grandpa;

	#[runtime::pallet_index(4)]
	pub type Balances = pallet_balances;

	#[runtime::pallet_index(5)]
	pub type TransactionPayment = pallet_transaction_payment;

	#[runtime::pallet_index(6)]
	pub type Sudo = pallet_sudo;

	// Include the custom logic from the pallet-template in the runtime.
	#[runtime::pallet_index(7)]
	pub type TemplateModule = pallet_template;
}
```

## Features
- `#[runtime::runtime]` attached to a struct defines the main runtime
- `#[runtime::derive]` attached to this struct defines the types
generated by runtime
- `#[runtime::pallet_index]` must be attached to a pallet to define its
index
- `#[runtime::disable_call]` can be optionally attached to a pallet to
disable its calls
- `#[runtime::disable_unsigned]` can be optionally attached to a pallet
to disable unsigned calls
- A pallet instance can be defined as `TemplateModule:
pallet_template<Instance>`
- An optional attribute can be defined as
`#[frame_support::runtime(legacy_ordering)]` to ensure that the order of
hooks is same as the order of pallets (and not based on the
pallet_index). This is to support legacy runtimes and should be avoided
for new ones.

## Todo
- [x] Update the latest syntax in kitchensink and tests
- [x] Update UI tests
- [x] Docs

## Extension
- Abstract away the Executive similar to
https://github.com/paritytech/substrate/pull/14742
- Optionally avoid the need to specify all runtime types (TBD)

---------

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: Nikhil Gupta <>

substrate/frame/support/Cargo.toml

@@ -109,7 +109,9 @@ try-runtime = [
 	"sp-debug-derive/force-debug",
 	"sp-runtime/try-runtime",
 ]
-experimental = []
+experimental = [
+	"frame-support-procedural/experimental",
+]
 # By default some types have documentation, `no-metadata-docs` allows to reduce the documentation
 # in the metadata.
 no-metadata-docs = [