feat: Add convenience method for constructing key to access account's…

… balance for a given denom (backport cosmos#12674) (cosmos#12745) (#352)

* feat: Add convenience method for constructing key to access account's balance for a given denom (cosmos#12674)

This PR adds a convenience method for constructing the key necessary to query for the account's balance of a given denom.

I ran into this issue since we are using ABCI query now to perform balance requests because we are also requesting merkle proofs for the returned balance [here](https://github.com/celestiaorg/celestia-node/pull/911/files#diff-0ee31f5a7bd88e9f758e6bebdf3ee36365519e55a451098d9638c39afe5eac42R144).

It would be nice to have a definitive convenience method for constructing the key.

[Ref.](github.com/celestiaorg/celestia-node/pull/911)

(cherry picked from commit a1777a8)

* Update CHANGELOG.md

* fix conflict

Co-authored-by: rene <41963722+renaynay@users.noreply.github.com>
Co-authored-by: Marko <marbar3778@yahoo.com>

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: rene <41963722+renaynay@users.noreply.github.com>
Co-authored-by: Marko <marbar3778@yahoo.com>
Co-authored-by: Roman <roman@osmosis.team>

x/bank/legacy/v043/store_test.go

@@ -90,13 +90,13 @@ func TestBalanceKeysMigration(t *testing.T) {
 	err = v043bank.MigrateStore(ctx, bankKey, encCfg.Marshaler)
 	require.NoError(t, err)
 
-	newKey := append(types.CreateAccountBalancesPrefix(addr), []byte(fooCoin.Denom)...)
+	newKey := types.CreatePrefixedAccountStoreKey(addr, []byte(fooCoin.Denom))
 	// -7 because we replaced "balances" with 0x02,
 	// +1 because we added length-prefix to address.
 	require.Equal(t, len(oldFooKey)-7+1, len(newKey))
 	require.Nil(t, store.Get(oldFooKey))
 	require.Equal(t, fooBz, store.Get(newKey))
 
-	newKeyFooBar := append(types.CreateAccountBalancesPrefix(addr), []byte(fooBarCoin.Denom)...)
+	newKeyFooBar := types.CreatePrefixedAccountStoreKey(addr, []byte(fooBarCoin.Denom))
 	require.Nil(t, store.Get(newKeyFooBar)) // after migration zero balances pruned from store.
 }

x/bank/types/key.go

@@ -57,3 +57,9 @@ func AddressFromBalancesStore(key []byte) (sdk.AccAddress, error) {
 func CreateAccountBalancesPrefix(addr []byte) []byte {
 	return append(BalancesPrefix, address.MustLengthPrefix(addr)...)
 }
+
+// CreatePrefixedAccountStoreKey returns the key for the given account and denomination.
+// This method can be used when performing an ABCI query for the balance of an account.
+func CreatePrefixedAccountStoreKey(addr []byte, denom []byte) []byte {
+	return append(CreateAccountBalancesPrefix(addr), denom...)
+}