fix(lib/trie): ClearFromChild should update parent trie

lib/trie/child_storage.go

@@ -111,14 +111,25 @@ func (t *Trie) ClearFromChild(keyToChild, key []byte) error {
 	if err != nil {
 		return err
 	}
+
 	if child == nil {
 		return fmt.Errorf("%w at key 0x%x%x", ErrChildTrieDoesNotExist, ChildStorageKeyPrefix, keyToChild)
 	}
 
+	origChildHash, err := child.Hash()
+	if err != nil {
+		return err
+	}
+
 	err = child.Delete(key)
 	if err != nil {
 		return fmt.Errorf("deleting from child trie located at key 0x%x: %w", keyToChild, err)
 	}
 
-	return nil
+	delete(t.childTries, origChildHash)
+	if child.root == nil {
+		return t.DeleteChild(keyToChild)
+	}
+
+	return t.SetChild(keyToChild, child)
 }

lib/trie/child_storage_test.go

@@ -5,8 +5,11 @@ package trie
 
 import (
 	"bytes"
+	"encoding/binary"
 	"reflect"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestPutAndGetChild(t *testing.T) {
@@ -71,3 +74,35 @@ func TestPutAndGetFromChild(t *testing.T) {
 		t.Fatalf("Fail: got %x expected %x", valueRes, testValue)
 	}
 }
+
+func TestChildTrieHashAfterClear(t *testing.T) {
+	trieThatHoldsAChildTrie := NewEmptyTrie()
+	originalEmptyHash := trieThatHoldsAChildTrie.MustHash()
+
+	keyToChild := []byte("crowdloan")
+	keyInChild := []byte("account-alice")
+	contributed := uint64(1000)
+	contributedWith := make([]byte, 8)
+	binary.BigEndian.PutUint64(contributedWith, contributed)
+
+	err := trieThatHoldsAChildTrie.PutIntoChild(keyToChild, keyInChild, contributedWith)
+	require.NoError(t, err)
+
+	// the parent trie hash SHOULT NOT BE EQUAL to the original
+	// empty hash since it contains a value
+	require.NotEqual(t, originalEmptyHash, trieThatHoldsAChildTrie.MustHash())
+
+	// ensure the value is inside the child trie
+	valueStored, err := trieThatHoldsAChildTrie.GetFromChild(keyToChild, keyInChild)
+	require.NoError(t, err)
+	require.Equal(t, contributed, binary.BigEndian.Uint64(valueStored))
+
+	// clear child trie key value
+	err = trieThatHoldsAChildTrie.ClearFromChild(keyToChild, keyInChild)
+	require.NoError(t, err)
+
+	// the parent trie hash SHOULD BE EQUAL to the original
+	// empty hash since now it does not have any other value in it
+	require.Equal(t, originalEmptyHash, trieThatHoldsAChildTrie.MustHash())
+
+}