[CALCITE-6323] Serialize return type during RelJson.toJson(RexNode no…

…de) for SqlKind.SAFE_CAST

core/src/main/java/org/apache/calcite/rel/externalize/RelJson.java

@@ -632,6 +632,7 @@ public Object toJson(RexNode node) {
         switch (node.getKind()) {
         case MINUS:
         case CAST:
+        case SAFE_CAST:
           map.put("type", toJson(node.getType()));
           break;
         default:

core/src/test/java/org/apache/calcite/plan/RelWriterTest.java

@@ -1091,6 +1091,36 @@ void testAggregateWithAlias(SqlExplainFormat format) {
     assertThat(result, isLinux(expected));
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-6323">[CALCITE-6323]</a>
+   *
+   * <p>Before the fix, RelJson.toRex would throw an ArrayIndexOutOfBounds error
+   * when deserializing SAFE_CAST due to type inference requiring 2 operands.
+   *
+   * <p>The solution is to add in 'type' when serializing to JSON.
+   */
+  @Test void testDeserializeSafeCastOperator() {
+    final FrameworkConfig config = RelBuilderTest.config().build();
+    final RelBuilder builder = RelBuilder.create(config);
+    final RexBuilder rb = builder.getRexBuilder();
+    final RelDataTypeFactory typeFactory = rb.getTypeFactory();
+    final RelDataType type = typeFactory.createSqlType(SqlTypeName.DATE);
+    final RelNode rel = builder
+        .scan("EMP")
+        .project(builder.field("JOB"),
+            rb.makeCall(type, SqlLibraryOperators.SAFE_CAST,
+                ImmutableList.of(builder.field("SAL")))).build();
+    final RelJsonWriter jsonWriter =
+        new RelJsonWriter(new JsonBuilder(), RelJson::withLibraryOperatorTable);
+    rel.explain(jsonWriter);
+    String relJson = jsonWriter.asString();
+    String result = deserializeAndDumpToTextFormat(getSchema(rel), relJson);
+    final String expected =
+        "LogicalProject(JOB=[$2], $f1=[SAFE_CAST($5)])\n"
+        + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    assertThat(result, isLinux(expected));
+  }
+
   @Test void testAggregateWithoutAlias() {
     final FrameworkConfig config = RelBuilderTest.config().build();
     final RelBuilder builder = RelBuilder.create(config);