Add an extra_constant to pallet-collator-selection (#7206)

Currently `pallet-collator-selection` does not expose a way to query the
assigned pot account derived from the `PotId` configuration item.
Without it, it is not possible to transfer the existential deposit to
it.

This PR addresses this issue by exposing an extra constant.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

cumulus/pallets/collator-selection/src/lib.rs

@@ -150,22 +150,27 @@ pub mod pallet {
 		type UpdateOrigin: EnsureOrigin<Self::RuntimeOrigin>;
 
 		/// Account Identifier from which the internal Pot is generated.
+		#[pallet::constant]
 		type PotId: Get<PalletId>;
 
 		/// Maximum number of candidates that we should have.
 		///
 		/// This does not take into account the invulnerables.
+		#[pallet::constant]
 		type MaxCandidates: Get<u32>;
 
 		/// Minimum number eligible collators. Should always be greater than zero. This includes
 		/// Invulnerable collators. This ensures that there will always be one collator who can
 		/// produce a block.
+		#[pallet::constant]
 		type MinEligibleCollators: Get<u32>;
 
 		/// Maximum number of invulnerables.
+		#[pallet::constant]
 		type MaxInvulnerables: Get<u32>;
 
 		// Will be kicked if block is not produced in threshold.
+		#[pallet::constant]
 		type KickThreshold: Get<BlockNumberFor<Self>>;
 
 		/// A stable ID for a validator.
@@ -183,6 +188,14 @@ pub mod pallet {
 		type WeightInfo: WeightInfo;
 	}
 
+	#[pallet::extra_constants]
+	impl<T: Config> Pallet<T> {
+		/// Gets this pallet's derived pot account.
+		fn pot_account() -> T::AccountId {
+			Self::account_id()
+		}
+	}
+
 	/// Basic information about a collation candidate.
 	#[derive(
 		PartialEq, Eq, Clone, Encode, Decode, RuntimeDebug, scale_info::TypeInfo, MaxEncodedLen,

prdoc/pr_7206.prdoc

+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: "Add an extra_constant to pallet-collator-selection"
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      - Allows to query collator-selection's pot account via extra constant.
+
+crates:
+  - name: pallet-collator-selection
+    bump: minor
\ No newline at end of file