viirya commented on code in PR #38823:
URL: https://github.com/apache/spark/pull/38823#discussion_r1116549456


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/GeneratedColumn.scala:
##########
@@ -0,0 +1,202 @@
+/*
+ * 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.spark.sql.catalyst.util
+
+import org.apache.spark.SparkException
+import org.apache.spark.sql.AnalysisException
+import org.apache.spark.sql.catalyst.analysis.Analyzer
+import org.apache.spark.sql.catalyst.expressions.{Alias, Cast, Expression}
+import org.apache.spark.sql.catalyst.parser.{CatalystSqlParser, ParseException}
+import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, Project}
+import org.apache.spark.sql.catalyst.trees.TreePattern.PLAN_EXPRESSION
+import 
org.apache.spark.sql.catalyst.util.ResolveDefaultColumns.BuiltInFunctionCatalog
+import org.apache.spark.sql.connector.catalog.{CatalogManager, TableCatalog, 
TableCatalogCapability}
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{DataType, StructField, StructType}
+
+/**
+ * This object contains utility methods and values for Generated Columns
+ */
+object GeneratedColumn {
+
+  /**
+   * The metadata key for saving a generation expression in a generated 
column's metadata. This is
+   * only used internally and connectors should access generation expressions 
from the V2 columns.
+   */
+  val GENERATION_EXPRESSION_METADATA_KEY = "generationExpression"
+
+  /** Parser for parsing generation expression SQL strings */
+  private lazy val parser = new CatalystSqlParser()
+
+  /**
+   * Whether the given `field` is a generated column
+   */
+  def isGeneratedColumn(field: StructField): Boolean = {
+    field.metadata.contains(GENERATION_EXPRESSION_METADATA_KEY)
+  }
+
+  /**
+   * Returns the generation expression stored in the column metadata if it 
exists
+   */
+  def getGenerationExpression(field: StructField): Option[String] = {
+    if (isGeneratedColumn(field)) {
+      Some(field.metadata.getString(GENERATION_EXPRESSION_METADATA_KEY))
+    } else {
+      None
+    }
+  }
+
+  /**
+   * Whether the `schema` has one or more generated columns
+   */
+  def hasGeneratedColumns(schema: StructType): Boolean = {
+    schema.exists(isGeneratedColumn)
+  }
+
+  /**
+   * Parse and analyze `expressionStr` and perform verification. This means:
+   * - The expression cannot reference itself
+   * - The expression cannot reference other generated columns
+   * - No user-defined expressions
+   * - The expression must be deterministic
+   * - The expression data type can be safely up-cast to the destination 
column data type
+   * - No subquery expressions
+   *
+   * Throws an [[AnalysisException]] if the expression cannot be converted or 
is an invalid
+   * generation expression according to the above rules.
+   */
+  private def analyzeAndVerifyExpression(
+      expressionStr: String,
+      fieldName: String,
+      dataType: DataType,
+      schema: StructType,
+      statementType: String): Unit = {
+    def unsupportedExpressionError(reason: String): AnalysisException = {
+      new AnalysisException(
+        errorClass = "UNSUPPORTED_EXPRESSION_GENERATED_COLUMN",
+        messageParameters = Map(
+          "fieldName" -> fieldName,
+          "expressionStr" -> expressionStr,
+          "reason" -> reason))
+    }
+
+    // Parse the expression string
+    val parsed: Expression = try {
+      parser.parseExpression(expressionStr)
+    } catch {
+      case ex: ParseException =>
+        // Shouldn't be possible since we check that the expression is a valid 
catalyst expression
+        // during parsing
+        throw SparkException.internalError(
+          s"Failed to execute $statementType command because the column 
$fieldName has " +
+            s"generation expression $expressionStr which fails to parse as a 
valid expression:" +
+            s"\n${ex.getMessage}")
+    }
+    // Don't allow subquery expressions
+    if (parsed.containsPattern(PLAN_EXPRESSION)) {
+      throw unsupportedExpressionError("subquery expressions are not allowed 
for generated columns")
+    }
+    // Analyze the parse result
+    val allowedBaseColumns = schema
+      .filterNot(_.name == fieldName) // Can't reference itself
+      .filterNot(isGeneratedColumn) // Can't reference other generated columns
+    val relation = new 
LocalRelation(StructType(allowedBaseColumns).toAttributes)
+    val plan = try {
+      val analyzer: Analyzer = GeneratedColumnAnalyzer
+      val analyzed = analyzer.execute(Project(Seq(Alias(parsed, fieldName)()), 
relation))
+      analyzer.checkAnalysis(analyzed)
+      analyzed
+    } catch {
+      case ex: AnalysisException =>
+        // Improve error message if possible
+        if (ex.getErrorClass == "UNRESOLVED_COLUMN.WITH_SUGGESTION") {
+          ex.messageParameters.get("objectName").foreach { unresolvedCol =>
+            // Check whether the unresolved column is this column (w.r.t. 
case-sensitivity)
+            val resolver = SQLConf.get.resolver
+            if (resolver(unresolvedCol, 
QueryCompilationErrors.toSQLId(fieldName))) {
+              // Generation expression references itself
+              throw unsupportedExpressionError("generation expression cannot 
reference itself")
+            }
+            // Check whether the unresolved column is another generated column 
in the schema
+            schema.filter(isGeneratedColumn).foreach { col =>
+              if (resolver(unresolvedCol, 
QueryCompilationErrors.toSQLId(col.name))) {
+                throw unsupportedExpressionError(
+                  "generation expression cannot reference another generated 
column")
+              }
+            }
+          }
+        }
+        if (ex.getErrorClass == "UNRESOLVED_ROUTINE") {
+          // Cannot resolve function using built-in catalog
+          ex.messageParameters.get("routineName").foreach { fnName =>
+            throw unsupportedExpressionError(s"failed to resolve $fnName to a 
built-in function")
+          }
+        }
+        throw ex
+    }
+    val analyzed = plan.collectFirst {
+      case Project(Seq(a: Alias), _: LocalRelation) => a.child
+    }.get
+    if (!analyzed.deterministic) {
+      throw unsupportedExpressionError("the expression is not deterministic")

Review Comment:
   ```suggestion
         throw unsupportedExpressionError("generation expression is not 
deterministic")
   ```



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/GeneratedColumn.scala:
##########
@@ -0,0 +1,202 @@
+/*
+ * 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.spark.sql.catalyst.util
+
+import org.apache.spark.SparkException
+import org.apache.spark.sql.AnalysisException
+import org.apache.spark.sql.catalyst.analysis.Analyzer
+import org.apache.spark.sql.catalyst.expressions.{Alias, Cast, Expression}
+import org.apache.spark.sql.catalyst.parser.{CatalystSqlParser, ParseException}
+import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, Project}
+import org.apache.spark.sql.catalyst.trees.TreePattern.PLAN_EXPRESSION
+import 
org.apache.spark.sql.catalyst.util.ResolveDefaultColumns.BuiltInFunctionCatalog
+import org.apache.spark.sql.connector.catalog.{CatalogManager, TableCatalog, 
TableCatalogCapability}
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{DataType, StructField, StructType}
+
+/**
+ * This object contains utility methods and values for Generated Columns
+ */
+object GeneratedColumn {
+
+  /**
+   * The metadata key for saving a generation expression in a generated 
column's metadata. This is
+   * only used internally and connectors should access generation expressions 
from the V2 columns.
+   */
+  val GENERATION_EXPRESSION_METADATA_KEY = "generationExpression"
+
+  /** Parser for parsing generation expression SQL strings */
+  private lazy val parser = new CatalystSqlParser()
+
+  /**
+   * Whether the given `field` is a generated column
+   */
+  def isGeneratedColumn(field: StructField): Boolean = {
+    field.metadata.contains(GENERATION_EXPRESSION_METADATA_KEY)
+  }
+
+  /**
+   * Returns the generation expression stored in the column metadata if it 
exists
+   */
+  def getGenerationExpression(field: StructField): Option[String] = {
+    if (isGeneratedColumn(field)) {
+      Some(field.metadata.getString(GENERATION_EXPRESSION_METADATA_KEY))
+    } else {
+      None
+    }
+  }
+
+  /**
+   * Whether the `schema` has one or more generated columns
+   */
+  def hasGeneratedColumns(schema: StructType): Boolean = {
+    schema.exists(isGeneratedColumn)
+  }
+
+  /**
+   * Parse and analyze `expressionStr` and perform verification. This means:
+   * - The expression cannot reference itself
+   * - The expression cannot reference other generated columns
+   * - No user-defined expressions
+   * - The expression must be deterministic
+   * - The expression data type can be safely up-cast to the destination 
column data type
+   * - No subquery expressions
+   *
+   * Throws an [[AnalysisException]] if the expression cannot be converted or 
is an invalid
+   * generation expression according to the above rules.
+   */
+  private def analyzeAndVerifyExpression(
+      expressionStr: String,
+      fieldName: String,
+      dataType: DataType,
+      schema: StructType,
+      statementType: String): Unit = {
+    def unsupportedExpressionError(reason: String): AnalysisException = {
+      new AnalysisException(
+        errorClass = "UNSUPPORTED_EXPRESSION_GENERATED_COLUMN",
+        messageParameters = Map(
+          "fieldName" -> fieldName,
+          "expressionStr" -> expressionStr,
+          "reason" -> reason))
+    }
+
+    // Parse the expression string
+    val parsed: Expression = try {
+      parser.parseExpression(expressionStr)
+    } catch {
+      case ex: ParseException =>
+        // Shouldn't be possible since we check that the expression is a valid 
catalyst expression
+        // during parsing
+        throw SparkException.internalError(
+          s"Failed to execute $statementType command because the column 
$fieldName has " +
+            s"generation expression $expressionStr which fails to parse as a 
valid expression:" +
+            s"\n${ex.getMessage}")
+    }
+    // Don't allow subquery expressions
+    if (parsed.containsPattern(PLAN_EXPRESSION)) {
+      throw unsupportedExpressionError("subquery expressions are not allowed 
for generated columns")
+    }
+    // Analyze the parse result

Review Comment:
   nit:
   ```suggestion
       // Analyze the parsed result
   ```



##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/GeneratedColumn.scala:
##########
@@ -0,0 +1,202 @@
+/*
+ * 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.spark.sql.catalyst.util
+
+import org.apache.spark.SparkException
+import org.apache.spark.sql.AnalysisException
+import org.apache.spark.sql.catalyst.analysis.Analyzer
+import org.apache.spark.sql.catalyst.expressions.{Alias, Cast, Expression}
+import org.apache.spark.sql.catalyst.parser.{CatalystSqlParser, ParseException}
+import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, Project}
+import org.apache.spark.sql.catalyst.trees.TreePattern.PLAN_EXPRESSION
+import 
org.apache.spark.sql.catalyst.util.ResolveDefaultColumns.BuiltInFunctionCatalog
+import org.apache.spark.sql.connector.catalog.{CatalogManager, TableCatalog, 
TableCatalogCapability}
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{DataType, StructField, StructType}
+
+/**
+ * This object contains utility methods and values for Generated Columns
+ */
+object GeneratedColumn {
+
+  /**
+   * The metadata key for saving a generation expression in a generated 
column's metadata. This is
+   * only used internally and connectors should access generation expressions 
from the V2 columns.
+   */
+  val GENERATION_EXPRESSION_METADATA_KEY = "generationExpression"
+
+  /** Parser for parsing generation expression SQL strings */
+  private lazy val parser = new CatalystSqlParser()
+
+  /**
+   * Whether the given `field` is a generated column
+   */
+  def isGeneratedColumn(field: StructField): Boolean = {
+    field.metadata.contains(GENERATION_EXPRESSION_METADATA_KEY)
+  }
+
+  /**
+   * Returns the generation expression stored in the column metadata if it 
exists
+   */
+  def getGenerationExpression(field: StructField): Option[String] = {
+    if (isGeneratedColumn(field)) {
+      Some(field.metadata.getString(GENERATION_EXPRESSION_METADATA_KEY))
+    } else {
+      None
+    }
+  }
+
+  /**
+   * Whether the `schema` has one or more generated columns
+   */
+  def hasGeneratedColumns(schema: StructType): Boolean = {
+    schema.exists(isGeneratedColumn)
+  }
+
+  /**
+   * Parse and analyze `expressionStr` and perform verification. This means:
+   * - The expression cannot reference itself
+   * - The expression cannot reference other generated columns
+   * - No user-defined expressions
+   * - The expression must be deterministic
+   * - The expression data type can be safely up-cast to the destination 
column data type
+   * - No subquery expressions
+   *
+   * Throws an [[AnalysisException]] if the expression cannot be converted or 
is an invalid
+   * generation expression according to the above rules.
+   */
+  private def analyzeAndVerifyExpression(
+      expressionStr: String,
+      fieldName: String,
+      dataType: DataType,
+      schema: StructType,
+      statementType: String): Unit = {
+    def unsupportedExpressionError(reason: String): AnalysisException = {
+      new AnalysisException(
+        errorClass = "UNSUPPORTED_EXPRESSION_GENERATED_COLUMN",
+        messageParameters = Map(
+          "fieldName" -> fieldName,
+          "expressionStr" -> expressionStr,
+          "reason" -> reason))
+    }
+
+    // Parse the expression string
+    val parsed: Expression = try {
+      parser.parseExpression(expressionStr)
+    } catch {
+      case ex: ParseException =>
+        // Shouldn't be possible since we check that the expression is a valid 
catalyst expression
+        // during parsing
+        throw SparkException.internalError(
+          s"Failed to execute $statementType command because the column 
$fieldName has " +
+            s"generation expression $expressionStr which fails to parse as a 
valid expression:" +
+            s"\n${ex.getMessage}")
+    }
+    // Don't allow subquery expressions
+    if (parsed.containsPattern(PLAN_EXPRESSION)) {
+      throw unsupportedExpressionError("subquery expressions are not allowed 
for generated columns")
+    }
+    // Analyze the parse result
+    val allowedBaseColumns = schema
+      .filterNot(_.name == fieldName) // Can't reference itself
+      .filterNot(isGeneratedColumn) // Can't reference other generated columns
+    val relation = new 
LocalRelation(StructType(allowedBaseColumns).toAttributes)
+    val plan = try {
+      val analyzer: Analyzer = GeneratedColumnAnalyzer
+      val analyzed = analyzer.execute(Project(Seq(Alias(parsed, fieldName)()), 
relation))
+      analyzer.checkAnalysis(analyzed)
+      analyzed
+    } catch {
+      case ex: AnalysisException =>
+        // Improve error message if possible
+        if (ex.getErrorClass == "UNRESOLVED_COLUMN.WITH_SUGGESTION") {
+          ex.messageParameters.get("objectName").foreach { unresolvedCol =>
+            // Check whether the unresolved column is this column (w.r.t. 
case-sensitivity)
+            val resolver = SQLConf.get.resolver
+            if (resolver(unresolvedCol, 
QueryCompilationErrors.toSQLId(fieldName))) {
+              // Generation expression references itself
+              throw unsupportedExpressionError("generation expression cannot 
reference itself")
+            }
+            // Check whether the unresolved column is another generated column 
in the schema
+            schema.filter(isGeneratedColumn).foreach { col =>
+              if (resolver(unresolvedCol, 
QueryCompilationErrors.toSQLId(col.name))) {
+                throw unsupportedExpressionError(
+                  "generation expression cannot reference another generated 
column")
+              }
+            }
+          }
+        }
+        if (ex.getErrorClass == "UNRESOLVED_ROUTINE") {
+          // Cannot resolve function using built-in catalog
+          ex.messageParameters.get("routineName").foreach { fnName =>
+            throw unsupportedExpressionError(s"failed to resolve $fnName to a 
built-in function")
+          }
+        }
+        throw ex
+    }
+    val analyzed = plan.collectFirst {
+      case Project(Seq(a: Alias), _: LocalRelation) => a.child
+    }.get
+    if (!analyzed.deterministic) {
+      throw unsupportedExpressionError("the expression is not deterministic")
+    }
+    if (!Cast.canUpCast(analyzed.dataType, dataType)) {
+      throw unsupportedExpressionError(
+        s"the expression data type ${analyzed.dataType.simpleString} " +
+        s"is incompatible with column data type ${dataType.simpleString}")

Review Comment:
   ```suggestion
           s"generation expression data type ${analyzed.dataType.simpleString} 
" +
           s"is incompatible with column data type ${dataType.simpleString}")
   ```



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