HHH-18497 Add xmlforest function

documentation/src/main/asciidoc/userguide/chapters/query/hql/QueryLanguage.adoc

@@ -2173,6 +2173,7 @@ it is necessary to enable the `hibernate.query.hql.xml_functions_enabled` config
 
 | `xmlelement()` | Constructs an XML element from arguments
 | `xmlcomment()` | Constructs an XML comment from the single argument
+| `xmlforest()` | Constructs an XML forest from thearguments
 |===
 
 
@@ -2208,7 +2209,7 @@ include::{xml-example-dir-hql}/XmlElementTest.java[tags=hql-xmlelement-attribute
 ----
 ====
 
-WARNING: SAP HANA, MySQL, MariaDB, H2 and HSQLDB do not support this function.
+WARNING: SAP HANA, MySQL, MariaDB and HSQLDB do not support this function.
 
 [[hql-xmlcomment-function]]
 ===== `xmlcomment()`
@@ -2223,7 +2224,31 @@ include::{xml-example-dir-hql}/XmlCommentTest.java[tags=hql-xmlcomment-example]
 ----
 ====
 
-WARNING: SAP HANA, MySQL, MariaDB, H2 and HSQLDB do not support this function.
+WARNING: SAP HANA, MySQL, MariaDB and HSQLDB do not support this function.
+
+[[hql-xmlforest-function]]
+===== `xmlforest()`
+
+Constructs an XML forest from the arguments. A forest is a sequence of XML elements.
+
+[[hql-xmlforest-bnf]]
+[source, antlrv4, indent=0]
+----
+include::{extrasdir}/xmlforest_bnf.txt[]
+----
+
+The optional name specifies the XML element name to use for the content as produced by the expression.
+The name can be omitted if a path expression is passed, in which case the last attribute name is used as element name.
+
+[[hql-xmlforest-example]]
+====
+[source, java, indent=0]
+----
+include::{xml-example-dir-hql}/XmlForestTest.java[tags=hql-xmlforest-example]
+----
+====
+
+WARNING: SAP HANA, MySQL, MariaDB and HSQLDB do not support this function.
 
 [[hql-user-defined-functions]]
 ==== Native and user-defined functions

documentation/src/main/asciidoc/userguide/chapters/query/hql/extras/xmlforest_bnf.txt

@@ -0,0 +1 @@
+"xmlforest(expressionOrPredicate ("as" identifier)? ("," expressionOrPredicate ("as" identifier)?)* ")"

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/DB2LegacyDialect.java

@@ -443,6 +443,7 @@ public class DB2LegacyDialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 	}
 
 	@Override

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/H2LegacyDialect.java

@@ -420,6 +420,7 @@ public class H2LegacyDialect extends Dialect {
 
 			functionFactory.xmlelement_h2();
 			functionFactory.xmlcomment();
+			functionFactory.xmlforest_h2();
 		}
 		else {
 			functionFactory.listagg_groupConcat();

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/OracleLegacyDialect.java

@@ -328,6 +328,7 @@ public class OracleLegacyDialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 	}
 
 	@Override

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/PostgreSQLLegacyDialect.java

@@ -671,6 +671,7 @@ public class PostgreSQLLegacyDialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 
 		if ( getVersion().isSameOrAfter( 9, 4 ) ) {
 			functionFactory.makeDateTimeTimestamp();

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/SQLServerLegacyDialect.java

@@ -415,6 +415,7 @@ public class SQLServerLegacyDialect extends AbstractTransactSQLDialect {
 		}
 		functionFactory.xmlelement_sqlserver();
 		functionFactory.xmlcomment_sqlserver();
+		functionFactory.xmlforest_sqlserver();
 		if ( getVersion().isSameOrAfter( 14 ) ) {
 			functionFactory.listagg_stringAggWithinGroup( "varchar(max)" );
 			functionFactory.jsonArrayAgg_sqlserver( getVersion().isSameOrAfter( 16 ) );

hibernate-core/src/main/antlr/org/hibernate/grammars/hql/HqlLexer.g4

@@ -332,6 +332,7 @@ WITHOUT				: [wW] [iI] [tT] [hH] [oO] [uU] [tT];
 WRAPPER				: [wW] [rR] [aA] [pP] [pP] [eE] [rR];
 XMLATTRIBUTES		: [xX] [mM] [lL] [aA] [tT] [tT] [rR] [iI] [bB] [uU] [tT] [eE] [sS];
 XMLELEMENT			: [xX] [mM] [lL] [eE] [lL] [eE] [mM] [eE] [nN] [tT];
+XMLFOREST			: [xX] [mM] [lL] [fF] [oO] [rR] [eE] [sS] [tT];
 YEAR				: [yY] [eE] [aA] [rR];
 ZONED				: [zZ] [oO] [nN] [eE] [dD];
 

hibernate-core/src/main/antlr/org/hibernate/grammars/hql/HqlParser.g4

@@ -1719,6 +1719,7 @@ jsonUniqueKeysClause
 
 xmlFunction
 	: xmlelementFunction
+	| xmlforestFunction
 	;
 
 /**
@@ -1735,6 +1736,13 @@ xmlattributesFunction
 	: XMLATTRIBUTES LEFT_PAREN expressionOrPredicate AS identifier (COMMA expressionOrPredicate AS identifier)* RIGHT_PAREN
 	;
 
+/**
+ * The 'xmlforest()' function
+ */
+xmlforestFunction
+	: XMLFOREST LEFT_PAREN expressionOrPredicate (AS identifier)? (COMMA expressionOrPredicate (AS identifier)?)* RIGHT_PAREN
+	;
+
 /**
  * Support for "soft" keywords which may be used as identifiers
  *
@@ -1943,6 +1951,7 @@ xmlattributesFunction
 	| WRAPPER
 	| XMLATTRIBUTES
 	| XMLELEMENT
+	| XMLFOREST
 	| YEAR
 	| ZONED) {
 		logUseOfReservedWordAsIdentifier( getCurrentToken() );

hibernate-core/src/main/java/org/hibernate/dialect/DB2Dialect.java

@@ -428,6 +428,7 @@ public class DB2Dialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/H2Dialect.java

@@ -355,6 +355,7 @@ public class H2Dialect extends Dialect {
 
 		functionFactory.xmlelement_h2();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest_h2();
 	}
 
 	/**

hibernate-core/src/main/java/org/hibernate/dialect/OracleDialect.java

@@ -418,6 +418,7 @@ public class OracleDialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/PostgreSQLDialect.java

@@ -632,6 +632,7 @@ public class PostgreSQLDialect extends Dialect {
 
 		functionFactory.xmlelement();
 		functionFactory.xmlcomment();
+		functionFactory.xmlforest();
 
 		functionFactory.makeDateTimeTimestamp();
 		// Note that PostgreSQL doesn't support the OVER clause for ordered set-aggregate functions

hibernate-core/src/main/java/org/hibernate/dialect/SQLServerDialect.java

@@ -433,6 +433,7 @@ public class SQLServerDialect extends AbstractTransactSQLDialect {
 		}
 		functionFactory.xmlelement_sqlserver();
 		functionFactory.xmlcomment_sqlserver();
+		functionFactory.xmlforest_sqlserver();
 		if ( getVersion().isSameOrAfter( 14 ) ) {
 			functionFactory.listagg_stringAggWithinGroup( "varchar(max)" );
 			functionFactory.jsonArrayAgg_sqlserver( getVersion().isSameOrAfter( 16 ) );

hibernate-core/src/main/java/org/hibernate/dialect/function/CommonFunctionFactory.java

@@ -154,8 +154,11 @@ import org.hibernate.dialect.function.json.SQLServerJsonReplaceFunction;
 import org.hibernate.dialect.function.json.SQLServerJsonSetFunction;
 import org.hibernate.dialect.function.json.SQLServerJsonValueFunction;
 import org.hibernate.dialect.function.xml.H2XmlElementFunction;
+import org.hibernate.dialect.function.xml.H2XmlForestFunction;
 import org.hibernate.dialect.function.xml.SQLServerXmlElementFunction;
+import org.hibernate.dialect.function.xml.SQLServerXmlForestFunction;
 import org.hibernate.dialect.function.xml.XmlElementFunction;
+import org.hibernate.dialect.function.xml.XmlForestFunction;
 import org.hibernate.query.sqm.function.SqmFunctionRegistry;
 import org.hibernate.query.sqm.produce.function.ArgumentTypesValidator;
 import org.hibernate.query.sqm.produce.function.FunctionParameterType;
@@ -4134,7 +4137,7 @@ public class CommonFunctionFactory {
 	}
 
 	/**
-	 * Standard xmlcomment() function
+	 * SQL Server xmlcomment() function
 	 */
 	public void xmlcomment_sqlserver() {
 		functionRegistry.patternDescriptorBuilder( "xmlcomment", "cast(('<!--'+?1+'-->') AS xml)" )
@@ -4143,4 +4146,25 @@ public class CommonFunctionFactory {
 				.setInvariantType( typeConfiguration.getBasicTypeRegistry().resolve( String.class, SqlTypes.SQLXML ) )
 				.register();
 	}
+
+	/**
+	 * Standard xmlforest() function
+	 */
+	public void xmlforest() {
+		functionRegistry.register( "xmlforest", new XmlForestFunction( typeConfiguration ) );
+	}
+
+	/**
+	 * H2 xmlforest() function
+	 */
+	public void xmlforest_h2() {
+		functionRegistry.register( "xmlforest", new H2XmlForestFunction( typeConfiguration ) );
+	}
+
+	/**
+	 * SQL Server xmlforest() function
+	 */
+	public void xmlforest_sqlserver() {
+		functionRegistry.register( "xmlforest", new SQLServerXmlForestFunction( typeConfiguration ) );
+	}
 }

hibernate-core/src/main/java/org/hibernate/dialect/function/xml/H2XmlForestFunction.java

@@ -0,0 +1,45 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.dialect.function.xml;
+
+import java.util.List;
+
+import org.hibernate.query.ReturnableType;
+import org.hibernate.sql.ast.SqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAppender;
+import org.hibernate.sql.ast.tree.SqlAstNode;
+import org.hibernate.sql.ast.tree.expression.AliasedExpression;
+import org.hibernate.type.spi.TypeConfiguration;
+
+/**
+ * H2 xmlforest function.
+ */
+public class H2XmlForestFunction extends XmlForestFunction {
+
+	public H2XmlForestFunction(TypeConfiguration typeConfiguration) {
+		super( typeConfiguration );
+	}
+
+	@Override
+	public void render(
+			SqlAppender sqlAppender,
+			List<? extends SqlAstNode> sqlAstArguments,
+			ReturnableType<?> returnType,
+			SqlAstTranslator<?> walker) {
+		String separator = "";
+		sqlAppender.appendSql( '(' );
+		for ( SqlAstNode sqlAstArgument : sqlAstArguments ) {
+			final AliasedExpression expression = (AliasedExpression) sqlAstArgument;
+			sqlAppender.appendSql( separator );
+			sqlAppender.appendSql( "xmlnode(" );
+			sqlAppender.appendSingleQuoteEscapedString( expression.getAlias() );
+			sqlAppender.appendSql( ",null," );
+			expression.getExpression().accept( walker );
+			sqlAppender.appendSql( ",false)" );
+			separator = "||";
+		}
+		sqlAppender.appendSql( ')' );
+	}
+}

hibernate-core/src/main/java/org/hibernate/dialect/function/xml/SQLServerXmlForestFunction.java

@@ -0,0 +1,45 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.dialect.function.xml;
+
+import java.util.List;
+
+import org.hibernate.query.ReturnableType;
+import org.hibernate.sql.ast.SqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAppender;
+import org.hibernate.sql.ast.tree.SqlAstNode;
+import org.hibernate.sql.ast.tree.expression.AliasedExpression;
+import org.hibernate.type.spi.TypeConfiguration;
+
+/**
+ * SQL Server xmlforest function.
+ */
+public class SQLServerXmlForestFunction extends XmlForestFunction {
+
+	public SQLServerXmlForestFunction(TypeConfiguration typeConfiguration) {
+		super( typeConfiguration );
+	}
+
+	@Override
+	public void render(
+			SqlAppender sqlAppender,
+			List<? extends SqlAstNode> sqlAstArguments,
+			ReturnableType<?> returnType,
+			SqlAstTranslator<?> walker) {
+		sqlAppender.appendSql( "cast" );
+		char separator = '(';
+		for ( SqlAstNode sqlAstArgument : sqlAstArguments ) {
+			final AliasedExpression expression = (AliasedExpression) sqlAstArgument;
+			sqlAppender.appendSql( separator );
+			sqlAppender.appendSql( "cast((select 1 tag,null parent," );
+			expression.getExpression().accept( walker );
+			sqlAppender.appendSql( " [" );
+			sqlAppender.appendSql( expression.getAlias() );
+			sqlAppender.appendSql( "!1] for xml explicit,type) as nvarchar(max))" );
+			separator = '+';
+		}
+		sqlAppender.appendSql( " as xml)" );
+	}
+}

hibernate-core/src/main/java/org/hibernate/dialect/function/xml/XmlElementFunction.java

@@ -60,7 +60,6 @@ public class XmlElementFunction extends AbstractSqmSelfRenderingFunctionDescript
 									throw new FunctionArgumentException(
 											String.format(
 													"Invalid XML element name passed to 'xmlelement()': %s",
-													1,
 													elementName
 											)
 									);
@@ -73,7 +72,6 @@ public class XmlElementFunction extends AbstractSqmSelfRenderingFunctionDescript
 											throw new FunctionArgumentException(
 													String.format(
 															"Invalid XML attribute name passed to 'xmlattributes()': %s",
-															1,
 															entry.getKey()
 													)
 											);

hibernate-core/src/main/java/org/hibernate/dialect/function/xml/XmlForestFunction.java

@@ -0,0 +1,119 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.dialect.function.xml;
+
+import java.util.List;
+
+import org.hibernate.query.ReturnableType;
+import org.hibernate.query.sqm.function.AbstractSqmSelfRenderingFunctionDescriptor;
+import org.hibernate.query.sqm.function.FunctionKind;
+import org.hibernate.query.sqm.produce.function.ArgumentsValidator;
+import org.hibernate.query.sqm.produce.function.FunctionArgumentException;
+import org.hibernate.query.sqm.produce.function.StandardArgumentsValidators;
+import org.hibernate.query.sqm.produce.function.StandardFunctionReturnTypeResolvers;
+import org.hibernate.query.sqm.tree.SqmTypedNode;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
+import org.hibernate.sql.ast.SqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAppender;
+import org.hibernate.sql.ast.tree.SqlAstNode;
+import org.hibernate.sql.ast.tree.expression.AliasedExpression;
+import org.hibernate.type.SqlTypes;
+import org.hibernate.type.spi.TypeConfiguration;
+
+import static java.lang.Character.isLetter;
+import static java.lang.Character.isLetterOrDigit;
+
+/**
+ * Standard XmlForestFunction function.
+ */
+public class XmlForestFunction extends AbstractSqmSelfRenderingFunctionDescriptor {
+
+	public XmlForestFunction(TypeConfiguration typeConfiguration) {
+		super(
+				"xmlforest",
+				FunctionKind.NORMAL,
+				StandardArgumentsValidators.composite(
+						StandardArgumentsValidators.min( 1 ),
+						new ArgumentsValidator() {
+							@Override
+							public void validate(
+									List<? extends SqmTypedNode<?>> arguments,
+									String functionName,
+									TypeConfiguration typeConfiguration) {
+								for ( int i = 0; i < arguments.size(); i++ ) {
+									SqmTypedNode<?> argument = arguments.get( i );
+									if ( !( argument instanceof SqmNamedExpression<?> namedExpression ) ) {
+										throw new FunctionArgumentException(
+												String.format(
+														"Parameter %d of function 'xmlforest()' is not named",
+														i
+												)
+										);
+									}
+									if ( !isValidXmlName( namedExpression.getName() ) ) {
+										throw new FunctionArgumentException(
+												String.format(
+														"Invalid XML element name passed to 'xmlforest()': %s",
+														namedExpression.getName()
+												)
+										);
+									}
+								}
+							}
+
+							private static boolean isValidXmlName(String name) {
+								if ( name.isEmpty()
+										|| !isValidXmlNameStart( name.charAt( 0 ) )
+										|| name.regionMatches( true, 0, "xml", 0, 3 ) ) {
+									return false;
+								}
+								for ( int i = 1; i < name.length(); i++ ) {
+									if ( !isValidXmlNameChar( name.charAt( i ) ) ) {
+										return false;
+									}
+								}
+								return true;
+							}
+
+							private static boolean isValidXmlNameStart(char c) {
+								return isLetter( c ) || c == '_' || c == ':';
+							}
+
+							private static boolean isValidXmlNameChar(char c) {
+								return isLetterOrDigit( c ) || c == '_' || c == ':' || c == '-' || c == '.';
+							}
+
+						}
+				),
+				StandardFunctionReturnTypeResolvers.invariant(
+						typeConfiguration.getBasicTypeRegistry().resolve( String.class, SqlTypes.SQLXML )
+				),
+				null
+		);
+	}
+
+	@Override
+	public void render(
+			SqlAppender sqlAppender,
+			List<? extends SqlAstNode> sqlAstArguments,
+			ReturnableType<?> returnType,
+			SqlAstTranslator<?> walker) {
+		sqlAppender.appendSql( "xmlforest" );
+		char separator = '(';
+		for ( SqlAstNode sqlAstArgument : sqlAstArguments ) {
+			sqlAppender.appendSql( separator );
+			if ( sqlAstArgument instanceof AliasedExpression aliasedExpression ) {
+				aliasedExpression.getExpression().accept( walker );
+				sqlAppender.appendSql( " as " );
+				sqlAppender.appendDoubleQuoteEscapedString( aliasedExpression.getAlias() );
+			}
+			else {
+				sqlAstArgument.accept( walker );
+			}
+			separator = ',';
+		}
+		sqlAppender.appendSql( ')' );
+	}
+}

hibernate-core/src/main/java/org/hibernate/query/criteria/HibernateCriteriaBuilder.java

@@ -4063,6 +4063,33 @@ public interface HibernateCriteriaBuilder extends CriteriaBuilder {
 	@Incubating
 	JpaExpression<String> xmlcomment(String comment);
 
+	/**
+	 * Creates an XML forest from the given XML element expressions.
+	 *
+	 * @since 7.0
+	 */
+	@Incubating
+	JpaExpression<String> xmlforest(Expression<?>... elements);
+
+	/**
+	 * Creates an XML forest from the given XML element expressions.
+	 *
+	 * @since 7.0
+	 */
+	@Incubating
+	JpaExpression<String> xmlforest(List<? extends Expression<?>> elements);
+
+	/**
+	 * Creates a named expression. The name is important for the result of the expression,
+	 * e.g. when building an {@code xmlforest}, the name acts as the XML element name.
+	 *
+	 * @since 7.0
+	 * @see #xmlforest(Expression[])
+	 * @see #xmlforest(List)
+	 */
+	@Incubating
+	<T> JpaExpression<T> named(Expression<T> expression, String name);
+
 	@Override
 	JpaPredicate and(List<Predicate> restrictions);
 

hibernate-core/src/main/java/org/hibernate/query/criteria/spi/HibernateCriteriaBuilderDelegate.java

@@ -3644,4 +3644,22 @@ public class HibernateCriteriaBuilderDelegate implements HibernateCriteriaBuilde
 	public JpaExpression<String> xmlcomment(String comment) {
 		return criteriaBuilder.xmlcomment( comment );
 	}
+
+	@Override
+	@Incubating
+	public JpaExpression<String> xmlforest(Expression<?>... elements) {
+		return criteriaBuilder.xmlforest( elements );
+	}
+
+	@Override
+	@Incubating
+	public JpaExpression<String> xmlforest(List<? extends Expression<?>> elements) {
+		return criteriaBuilder.xmlforest( elements );
+	}
+
+	@Override
+	@Incubating
+	public <T> JpaExpression<T> named(Expression<T> expression, String name) {
+		return criteriaBuilder.named( expression, name );
+	}
 }

hibernate-core/src/main/java/org/hibernate/query/hql/internal/SemanticQueryBuilder.java

@@ -153,6 +153,7 @@ import org.hibernate.query.sqm.tree.expression.SqmJsonValueExpression;
 import org.hibernate.query.sqm.tree.expression.SqmLiteral;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEntityType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralNull;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmNamedParameter;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
 import org.hibernate.query.sqm.tree.expression.SqmOverflow;
@@ -3004,6 +3005,33 @@ public class SemanticQueryBuilder<R> extends HqlParserBaseVisitor<Object> implem
 		return xmlelement;
 	}
 
+	@Override
+	public SqmExpression<?> visitXmlforestFunction(HqlParser.XmlforestFunctionContext ctx) {
+		checkXmlFunctionsEnabled( ctx );
+		final ArrayList<SqmExpression<?>> elementExpressions = new ArrayList<>( ctx.getChildCount() >> 1 );
+		for ( int i = 2; i < ctx.getChildCount(); i++ ) {
+			if ( ctx.getChild( i ) instanceof HqlParser.ExpressionOrPredicateContext exprCtx ) {
+				final SqmExpression<?> expression = (SqmExpression<?>) exprCtx.accept( this );
+				if ( i + 2 < ctx.getChildCount() && ctx.getChild( i + 2 ) instanceof HqlParser.IdentifierContext identifierContext ) {
+					final String name = visitIdentifier( identifierContext );
+					elementExpressions.add( new SqmNamedExpression<>( expression, name ) );
+					i += 2;
+				}
+				else {
+					if ( !( expression instanceof SqmPath<?> path ) || !( path.getModel() instanceof PersistentAttribute<?, ?> attribute ) ) {
+						throw new SemanticException(
+								"Can't use expression '" + exprCtx.getText() + " without explicit name in xmlforest function" +
+										", because XML element names can only be derived from path expressions.",
+								query
+						);
+					}
+					elementExpressions.add( new SqmNamedExpression<>( expression, attribute.getName() ) );
+				}
+			}
+		}
+		return creationContext.getNodeBuilder().xmlforest( elementExpressions );
+	}
+
 	private void checkXmlFunctionsEnabled(ParserRuleContext ctx) {
 		if ( !creationOptions.isXmlFunctionsEnabled() ) {
 			throw new SemanticException(

hibernate-core/src/main/java/org/hibernate/query/sqm/NodeBuilder.java

@@ -756,6 +756,15 @@ public interface NodeBuilder extends HibernateCriteriaBuilder, BindingContext {
 	@Override
 	SqmExpression<String> xmlcomment(String comment);
 
+	@Override
+	<T> SqmExpression<T> named(Expression<T> expression, String name);
+
+	@Override
+	SqmExpression<String> xmlforest(List<? extends Expression<?>> elements);
+
+	@Override
+	SqmExpression<String> xmlforest(Expression<?>... elements);
+
 	// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 	// Covariant overrides
 

hibernate-core/src/main/java/org/hibernate/query/sqm/SemanticQueryWalker.java

@@ -69,6 +69,7 @@ import org.hibernate.query.sqm.tree.expression.SqmLiteral;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEmbeddableType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEntityType;
 import org.hibernate.query.sqm.tree.expression.SqmModifiedSubQueryExpression;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmNamedParameter;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
 import org.hibernate.query.sqm.tree.expression.SqmOverflow;
@@ -418,4 +419,6 @@ public interface SemanticQueryWalker<T> {
 	T visitFullyQualifiedClass(Class<?> namedClass);
 
 	T visitAsWrapperExpression(AsWrapperSqmExpression<?> expression);
+
+	T visitNamedExpression(SqmNamedExpression<?> expression);
 }

hibernate-core/src/main/java/org/hibernate/query/sqm/internal/SqmCriteriaNodeBuilder.java

@@ -43,6 +43,7 @@ import org.hibernate.internal.util.collections.CollectionHelper;
 import org.hibernate.jpa.spi.JpaCompliance;
 import org.hibernate.metamodel.model.domain.DomainType;
 import org.hibernate.metamodel.model.domain.JpaMetamodel;
+import org.hibernate.metamodel.model.domain.PersistentAttribute;
 import org.hibernate.metamodel.model.domain.SingularPersistentAttribute;
 import org.hibernate.metamodel.spi.MappingMetamodelImplementor;
 import org.hibernate.query.BindableType;
@@ -128,6 +129,7 @@ import org.hibernate.query.sqm.tree.expression.SqmJsonValueExpression;
 import org.hibernate.query.sqm.tree.expression.SqmLiteral;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralNull;
 import org.hibernate.query.sqm.tree.expression.SqmModifiedSubQueryExpression;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
 import org.hibernate.query.sqm.tree.expression.SqmStar;
 import org.hibernate.query.sqm.tree.expression.SqmToDuration;
@@ -5696,4 +5698,38 @@ public class SqmCriteriaNodeBuilder implements NodeBuilder, Serializable {
 				queryEngine
 		);
 	}
+
+	@Override
+	public <T> SqmExpression<T> named(Expression<T> expression, String name) {
+		return new SqmNamedExpression<>( (SqmExpression<T>) expression, name );
+	}
+
+	@Override
+	public SqmExpression<String> xmlforest(Expression<?>... elements) {
+		return xmlforest( Arrays.asList( elements ) );
+	}
+
+	@Override
+	public SqmExpression<String> xmlforest(List<? extends Expression<?>> elements) {
+		final ArrayList<SqmExpression<?>> arguments = new ArrayList<>( elements.size() );
+		for ( Expression<?> expression : elements ) {
+			if ( expression instanceof SqmNamedExpression<?> ) {
+				arguments.add( (SqmNamedExpression<?>) expression );
+			}
+			else {
+				if ( !( expression instanceof SqmPath<?> path ) || !( path.getModel() instanceof PersistentAttribute<?, ?> attribute ) ) {
+					throw new SemanticException(
+							"Can't use expression '" + expression + " without explicit name in xmlforest function"+
+									", because XML element names can only be derived from path expressions."
+					);
+				}
+				arguments.add( new SqmNamedExpression<>( (SqmExpression<?>) expression, attribute.getName() ) );
+			}
+		}
+		return getFunctionDescriptor( "xmlforest" ).generateSqmExpression(
+				arguments,
+				null,
+				queryEngine
+		);
+	}
 }

hibernate-core/src/main/java/org/hibernate/query/sqm/internal/SqmTreePrinter.java

@@ -58,6 +58,7 @@ import org.hibernate.query.sqm.tree.expression.SqmLiteral;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEmbeddableType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEntityType;
 import org.hibernate.query.sqm.tree.expression.SqmModifiedSubQueryExpression;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmNamedParameter;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
 import org.hibernate.query.sqm.tree.expression.SqmOverflow;
@@ -1198,6 +1199,11 @@ public class SqmTreePrinter implements SemanticQueryWalker<Object> {
 		return null;
 	}
 
+	@Override
+	public Object visitNamedExpression(SqmNamedExpression<?> expression) {
+		return null;
+	}
+
 	@Override
 	public Object visitModifiedSubQueryExpression(SqmModifiedSubQueryExpression expression) {
 		return null;

hibernate-core/src/main/java/org/hibernate/query/sqm/spi/BaseSemanticQueryWalker.java

@@ -60,6 +60,7 @@ import org.hibernate.query.sqm.tree.expression.SqmLiteral;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEmbeddableType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEntityType;
 import org.hibernate.query.sqm.tree.expression.SqmModifiedSubQueryExpression;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmNamedParameter;
 import org.hibernate.query.sqm.tree.expression.SqmOrderedSetAggregateFunction;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
@@ -988,4 +989,10 @@ public abstract class BaseSemanticQueryWalker implements SemanticQueryWalker<Obj
 		expression.getExpression().accept( this );
 		return expression;
 	}
+
+	@Override
+	public Object visitNamedExpression(SqmNamedExpression<?> expression) {
+		expression.getExpression().accept( this );
+		return expression;
+	}
 }

hibernate-core/src/main/java/org/hibernate/query/sqm/sql/BaseSqmToSqlAstConverter.java

@@ -224,6 +224,7 @@ import org.hibernate.query.sqm.tree.expression.SqmLiteralEmbeddableType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralEntityType;
 import org.hibernate.query.sqm.tree.expression.SqmLiteralNull;
 import org.hibernate.query.sqm.tree.expression.SqmModifiedSubQueryExpression;
+import org.hibernate.query.sqm.tree.expression.SqmNamedExpression;
 import org.hibernate.query.sqm.tree.expression.SqmNamedParameter;
 import org.hibernate.query.sqm.tree.expression.SqmOver;
 import org.hibernate.query.sqm.tree.expression.SqmOverflow;
@@ -314,6 +315,7 @@ import org.hibernate.sql.ast.tree.cte.CteTable;
 import org.hibernate.sql.ast.tree.cte.CteTableGroup;
 import org.hibernate.sql.ast.tree.cte.SearchClauseSpecification;
 import org.hibernate.sql.ast.tree.delete.DeleteStatement;
+import org.hibernate.sql.ast.tree.expression.AliasedExpression;
 import org.hibernate.sql.ast.tree.expression.Any;
 import org.hibernate.sql.ast.tree.expression.BinaryArithmeticExpression;
 import org.hibernate.sql.ast.tree.expression.CaseSearchedExpression;
@@ -8325,6 +8327,11 @@ public abstract class BaseSqmToSqlAstConverter<T extends Statement> extends Base
 		);
 	}
 
+	@Override
+	public Object visitNamedExpression(SqmNamedExpression<?> expression) {
+		return new AliasedExpression( (Expression) expression.getExpression().accept( this ), expression.getName() );
+	}
+
 	@Override
 	public Fetch visitIdentifierFetch(EntityResultGraphNode fetchParent) {
 		final EntityIdentifierMapping identifierMapping = fetchParent.getReferencedMappingContainer()

hibernate-core/src/main/java/org/hibernate/query/sqm/tree/expression/SqmNamedExpression.java

@@ -0,0 +1,62 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.query.sqm.tree.expression;
+
+import org.hibernate.Incubating;
+import org.hibernate.query.sqm.SemanticQueryWalker;
+import org.hibernate.query.sqm.tree.SqmCopyContext;
+
+/**
+ * A named expression. Used when the name of the expression matters
+ * e.g. in XML generation.
+ *
+ * @since 7.0
+ */
+@Incubating
+public class SqmNamedExpression<T> extends AbstractSqmExpression<T> {
+
+	private final SqmExpression<T> expression;
+	private final String name;
+
+	public SqmNamedExpression(SqmExpression<T> expression, String name) {
+		super( expression.getExpressible(), expression.nodeBuilder() );
+		this.expression = expression;
+		this.name = name;
+	}
+
+	@Override
+	public SqmNamedExpression<T> copy(SqmCopyContext context) {
+		final SqmNamedExpression<T> existing = context.getCopy( this );
+		if ( existing != null ) {
+			return existing;
+		}
+		final SqmNamedExpression<T> expression = context.registerCopy(
+				this,
+				new SqmNamedExpression<>( this.expression.copy( context ), name )
+		);
+		copyTo( expression, context );
+		return expression;
+	}
+
+	public SqmExpression<T> getExpression() {
+		return expression;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	@Override
+	public <X> X accept(SemanticQueryWalker<X> walker) {
+		return walker.visitNamedExpression( this );
+	}
+
+	@Override
+	public void appendHqlString(StringBuilder sb) {
+		expression.appendHqlString( sb );
+		sb.append( " as " );
+		sb.append( name );
+	}
+}

hibernate-core/src/main/java/org/hibernate/sql/ast/tree/expression/AliasedExpression.java

@@ -36,4 +36,11 @@ public class AliasedExpression implements SelfRenderingExpression {
 		return expression.getExpressionType();
 	}
 
+	public Expression getExpression() {
+		return expression;
+	}
+
+	public String getAlias() {
+		return alias;
+	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/function/xml/XmlForestTest.java

@@ -0,0 +1,36 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.function.xml;
+
+import org.hibernate.cfg.QuerySettings;
+
+import org.hibernate.testing.orm.junit.DialectFeatureChecks;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.RequiresDialectFeature;
+import org.hibernate.testing.orm.junit.ServiceRegistry;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Christian Beikov
+ */
+@DomainModel
+@SessionFactory
+@ServiceRegistry(settings = @Setting(name = QuerySettings.XML_FUNCTIONS_ENABLED, value = "true"))
+@RequiresDialectFeature( feature = DialectFeatureChecks.SupportsXmlforest.class)
+public class XmlForestTest {
+
+	@Test
+	public void testSimple(SessionFactoryScope scope) {
+		scope.inSession( em -> {
+			//tag::hql-xmlforest-example[]
+			em.createQuery( "select xmlforest(123 as e1, 'text' as e2)" ).getResultList();
+			//end::hql-xmlforest-example[]
+		} );
+	}
+
+}

hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/XmlFunctionTests.java

@@ -153,6 +153,23 @@ public class XmlFunctionTests {
 		);
 	}
 
+	@Test
+	@RequiresDialectFeature(feature = DialectFeatureChecks.SupportsXmlforest.class)
+	public void testXmlforest(SessionFactoryScope scope) {
+		scope.inTransaction(
+				session -> {
+					Tuple tuple = session.createQuery(
+							"select xmlforest(123 as e1, 'text' as e2)," +
+									"xmlforest(e.id, e.theString) " +
+									"from EntityOfBasics e where e.id = 1",
+							Tuple.class
+					).getSingleResult();
+					assertXmlEquals( "<r><e1>123</e1><e2>text</e2></r>", "<r>" + tuple.get( 0, String.class ) + "</r>" );
+					assertXmlEquals( "<r><id>1</id><theString>Dog</theString></r>", "<r>" + tuple.get( 1, String.class ) + "</r>" );
+				}
+		);
+	}
+
 	private void assertXmlEquals(String expected, String actual) {
 		final Document expectedDoc = parseXml( xmlNormalize( expected ) );
 		final Document actualDoc = parseXml( xmlNormalize( actual ) );

hibernate-testing/src/main/java/org/hibernate/testing/orm/junit/DialectFeatureChecks.java

@@ -850,6 +850,12 @@ abstract public class DialectFeatureChecks {
 		}
 	}
 
+	public static class SupportsXmlforest implements DialectFeatureCheck {
+		public boolean apply(Dialect dialect) {
+			return definesFunction( dialect, "xmlforest" );
+		}
+	}
+
 	public static class IsJtds implements DialectFeatureCheck {
 		public boolean apply(Dialect dialect) {
 			return dialect instanceof SybaseDialect && ( (SybaseDialect) dialect ).getDriverKind() == SybaseDriverKind.JTDS;