Add regression test for merging large doc with small doc.

Author: nicktobey

go/store/prolly/tree/json_diff_test.go

@@ -287,10 +287,13 @@ func largeJsonDiffTests(t *testing.T) []jsonDiffTest {
 	ctx := sql.NewEmptyContext()
 	ns := NewTestNodeStore()
 
+	emptyDocument := types.JSONDocument{Val: types.JsonObject{}}
+
 	insert := func(document types.MutableJSON, path string, val interface{}) types.MutableJSON {
 		jsonVal, inRange, err := types.JSON.Convert(val)
 		require.NoError(t, err)
 		require.True(t, (bool)(inRange))
+		document = document.Clone(ctx).(types.MutableJSON)
 		newDoc, changed, err := document.Insert(ctx, path, jsonVal.(sql.JSONWrapper))
 		require.NoError(t, err)
 		require.True(t, changed)
@@ -400,6 +403,18 @@ func largeJsonDiffTests(t *testing.T) []jsonDiffTest {
 				},
 			},
 		},
+		{
+			// This is a regression test.
+			// If:
+			// - One document fits in a single chunk and the other doesn't
+			// - The location of the chunk boundary in the larger document is also present in the smaller document
+			// - The chunk boundary doesn't fall at the beginning of value.
+			// Then the differ would fail to advance the prolly tree cursor and would incorrectly see the larger document as corrupt.
+			// The values in this test case are specifically chosen to meet these conditions.
+			name: "no error when diffing large doc with small doc",
+			from: largeObject,
+			to:   insert(emptyDocument, "$.level6", insert(emptyDocument, "$.level4", lookup(largeObject, "$.level6.level4"))),
+		},
 	}
 }
 
@@ -473,9 +488,11 @@ func runTest(t *testing.T, test jsonDiffTest) {
 
 		return cmp == 0
 	}
-	require.Equal(t, len(test.expectedDiffs), len(actualDiffs))
-	for i, expected := range test.expectedDiffs {
-		actual := actualDiffs[i]
-		require.True(t, diffsEqual(expected, actual), fmt.Sprintf("Expected: %v\nActual: %v", expected, actual))
+	if test.expectedDiffs != nil {
+		require.Equal(t, len(test.expectedDiffs), len(actualDiffs))
+		for i, expected := range test.expectedDiffs {
+			actual := actualDiffs[i]
+			require.True(t, diffsEqual(expected, actual), fmt.Sprintf("Expected: %v\nActual: %v", expected, actual))
+		}
 	}
 }