[GitHub] [flink] twalthr commented on a change in pull request #18524: [FLINK-25428][table-common][table-planner] Expose string casting for map, multiset, structured, row and raw

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twalthr commented on a change in pull request #18524:
URL: https://github.com/apache/flink/pull/18524#discussion_r810873004



##########
File path: flink-core/src/main/java/org/apache/flink/util/CollectionUtil.java
##########
@@ -109,4 +110,22 @@ public static boolean isNullOrEmpty(Map<?, ?> map) {
         iterator.forEachRemaining(list::add);
         return list;
     }
+
+    /** Returns an immutable {@link Map.Entry}. */
+    public static <K, V> Map.Entry<K, V> entry(K k, V v) {

Review comment:
       please put core changes in a hotfix commit

##########
File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/logical/utils/LogicalTypeCasts.java
##########
@@ -318,11 +318,17 @@ private static boolean supportsCasting(
             // cast between interval and exact numeric is only supported if interval has a single
             // field
             return isSingleFieldInterval(targetType);
+        } else if ((sourceType.is(CONSTRUCTED) || sourceType.is(STRUCTURED_TYPE))
+                && targetType.is(CHARACTER_STRING)) {
+            return supportsCollectionAndStructuredToStringCasting(sourceType, allowExplicit);

Review comment:
       can't this also just always be `true`? What casting does not support to string?

##########
File path: flink-table/flink-table-planner/src/main/java/org/apache/calcite/sql/fun/SqlCastFunction.java
##########
@@ -0,0 +1,220 @@
+/*
+ * 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.calcite.sql.fun;
+
+import org.apache.flink.table.planner.calcite.FlinkTypeFactory;
+import org.apache.flink.table.types.logical.utils.LogicalTypeCasts;
+
+import com.google.common.collect.ImmutableSetMultimap;
+import com.google.common.collect.SetMultimap;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFamily;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlCallBinding;
+import org.apache.calcite.sql.SqlDynamicParam;
+import org.apache.calcite.sql.SqlFunction;
+import org.apache.calcite.sql.SqlFunctionCategory;
+import org.apache.calcite.sql.SqlIntervalQualifier;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.SqlLiteral;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlOperandCountRange;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.SqlSyntax;
+import org.apache.calcite.sql.SqlUtil;
+import org.apache.calcite.sql.SqlWriter;
+import org.apache.calcite.sql.type.InferTypes;
+import org.apache.calcite.sql.type.SqlOperandCountRanges;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.type.SqlTypeUtil;
+import org.apache.calcite.sql.validate.SqlMonotonicity;
+import org.apache.calcite.sql.validate.SqlValidatorImpl;
+
+import java.text.Collator;
+import java.util.Objects;
+
+import static org.apache.calcite.util.Static.RESOURCE;
+
+/**
+ * SqlCastFunction. Note that the std functions are really singleton objects, because they always
+ * get fetched via the StdOperatorTable. So you can't store any local info in the class and hence
+ * the return type data is maintained in operand[1] through the validation phase.
+ *
+ * <p>Can be used for both {@link SqlCall} and {@link org.apache.calcite.rex.RexCall}. Note that the
+ * {@code SqlCall} has two operands (expression and type), while the {@code RexCall} has one operand
+ * (expression) and the type is obtained from {@link org.apache.calcite.rex.RexNode#getType()}.
+ *
+ * <p>The class was copied over because of CALCITE-XXXX, in order to workaround the method {@link

Review comment:
       `CALCITE-XXXX`?




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