fix(trie): Panic when deleting nonexistent keys from trie (GSR-10) (#2609)

* add check for common key length

* add test case for nonexistent key

Author: edwardmack

lib/trie/trie.go

@@ -969,6 +969,10 @@ func (t *Trie) deleteBranch(branch *Node, key []byte) (
 	}
 
 	commonPrefixLength := lenCommonPrefix(branch.Key, key)
+	keyDoesNotExist := commonPrefixLength == len(key)
+	if keyDoesNotExist {
+		return branch, false, 0
+	}
 	childIndex := key[commonPrefixLength]
 	childKey := key[commonPrefixLength+1:]
 	child := branch.Children[childIndex]

lib/trie/trie_test.go

@@ -3573,6 +3573,40 @@ func Test_Trie_delete(t *testing.T) {
 			},
 			updated: true,
 		},
+		"handle nonexistent key (no op)": {
+			trie: Trie{
+				generation: 1,
+			},
+			parent: &Node{
+				Key:         []byte{1, 0, 2, 3},
+				Descendants: 1,
+				Children: padRightChildren([]*Node{
+					{ // full key 1, 0, 2
+						Key:   []byte{2},
+						Value: []byte{1},
+					},
+					{ // full key 1, 1, 2
+						Key:   []byte{2},
+						Value: []byte{2},
+					},
+				}),
+			},
+			key: []byte{1, 0, 2},
+			newParent: &Node{
+				Key:         []byte{1, 0, 2, 3},
+				Descendants: 1,
+				Children: padRightChildren([]*Node{
+					{ // full key 1, 0, 2
+						Key:   []byte{2},
+						Value: []byte{1},
+					},
+					{ // full key 1, 1, 2
+						Key:   []byte{2},
+						Value: []byte{2},
+					},
+				}),
+			},
+		},
 	}
 
 	for name, testCase := range testCases {