[FLINK-18090][core][table] Update Row#toString and provide legacy util

This updates the Row.toString method to provide a good summary string.

In particular it fixes the following issues:

Changeflag: According to FLIP-95, a row describes an entry in a
changelog. Therefore, it should visible whether a row is an insert,
delete, or update change. Now indicated with +I, -D, +U, -U.

Nested rows: In the old implementation it was not visible whether nested
rows exist or not due to missing start/end boundaries. Now indicated with
[...] or {...}.

Positioned rows vs. named rows: According to FLIP-136, it should be visible
whether a row operates in name-based or position-based field mode. Now
indicated with [...] or {...}.

Nested arrays in maps and lists: In the old implementation arrays in maps
or lists could not be represented.

Wrong formatting: Most programming languages use a space after a comma.

This is an incompatible change. If the legacy representation is still
required for tests, the old behavior can be restored via the flag
RowUtils.USE_LEGACY_TO_STRING for the local JVM. However, relying on
the row's string representation for tests is not a good idea in general as
field data types are not verified.

flink-core/src/main/java/org/apache/flink/types/RowUtils.java

@@ -74,6 +74,14 @@ public final class RowUtils {
     // Internal utilities
     // --------------------------------------------------------------------------------------------
 
+    /**
+     * Internal flag to enable the legacy {@link Row#toString()} implementation for tests. In
+     * general, tests should not depend on the string representation of rows but should fully
+     * compare instances (especially data types of fields). This flag will be dropped once all tests
+     * have been updated.
+     */
+    public static boolean USE_LEGACY_TO_STRING = false;
+
     /** Internal utility for creating a row in static named-position field mode. */
     @Internal
     public static Row createRowWithNamedPositions(
@@ -149,10 +157,12 @@ public final class RowUtils {
             @Nullable Map<String, Object> fieldByName) {
         final StringBuilder sb = new StringBuilder();
         if (fieldByPosition != null) {
-            // TODO enable this for FLINK-18090
-            // sb.append(kind.shortString());
-            // deepToStringArray(sb, fieldByPosition);
-            deepToStringArrayLegacy(sb, fieldByPosition);
+            if (USE_LEGACY_TO_STRING) {
+                deepToStringArrayLegacy(sb, fieldByPosition);
+            } else {
+                sb.append(kind.shortString());
+                deepToStringArray(sb, fieldByPosition);
+            }
         } else {
             assert fieldByName != null;
             sb.append(kind.shortString());

flink-core/src/test/java/org/apache/flink/types/RowTest.java

@@ -124,9 +124,7 @@ public class RowTest {
         assertThat(row.getField(2), equalTo(null));
 
         // test toString
-        // TODO enable this for FLINK-18090
-        // assertThat(row.toString(), equalTo("-D[42, true, null]"));
-        assertThat(row.toString(), equalTo("42,true,null"));
+        assertThat(row.toString(), equalTo("-D[42, true, null]"));
 
         // test override
         row.setField(0, 13);
@@ -155,9 +153,7 @@ public class RowTest {
         row.clear();
         assertThat(row.getArity(), equalTo(3));
         assertThat(row.getFieldNames(false), equalTo(null));
-        // TODO enable this for FLINK-18090
-        // assertThat(row.toString(), equalTo("-D[null, null, null]"));
-        assertThat(row.toString(), equalTo("null,null,null"));
+        assertThat(row.toString(), equalTo("-D[null, null, null]"));
 
         // test invalid setter
         try {
@@ -198,9 +194,7 @@ public class RowTest {
         assertThat(row.getField("c"), equalTo(null));
 
         // test toString
-        // TODO enable this for FLINK-18090
-        // assertThat(row.toString(), equalTo("-D[42, true, null]"));
-        assertThat(row.toString(), equalTo("42,true,null"));
+        assertThat(row.toString(), equalTo("-D[42, true, null]"));
 
         // test override
         row.setField("a", 13);
@@ -229,9 +223,7 @@ public class RowTest {
         row.clear();
         assertThat(row.getArity(), equalTo(3));
         assertThat(row.getFieldNames(true), contains("a", "b", "c"));
-        // TODO enable this for FLINK-18090
-        // assertThat(row.toString(), equalTo("-D[null, null, null]"));
-        assertThat(row.toString(), equalTo("null,null,null"));
+        assertThat(row.toString(), equalTo("-D[null, null, null]"));
 
         // test invalid setter
         try {

flink-table/flink-table-common/src/test/java/org/apache/flink/table/utils/LegacyRowResource.java

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.utils;
+
+import org.apache.flink.types.Row;
+import org.apache.flink.types.RowUtils;
+
+import org.junit.rules.ExternalResource;
+
+/**
+ * Enables the old behavior of {@link Row#toString()} for legacy tests.
+ *
+ * <p>It ignores the changes applied in FLINK-16998 and FLINK-19981.
+ */
+public class LegacyRowResource extends ExternalResource {
+
+    public static final LegacyRowResource INSTANCE = new LegacyRowResource();
+
+    private LegacyRowResource() {
+        // singleton
+    }
+
+    @Override
+    protected void before() {
+        RowUtils.USE_LEGACY_TO_STRING = true;
+    }
+
+    @Override
+    protected void after() {
+        RowUtils.USE_LEGACY_TO_STRING = false;
+    }
+}