add tests for trunc() and date_trunc(), even though they're non-"standard"

see https://hibernate.atlassian.net/browse/HHH-15855

Author: gavinking

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

@@ -276,6 +276,8 @@ public void initializeFunctionRegistry(QueryEngine queryEngine) {
 		if ( useLocalTime ) {
 			functionFactory.localtimeLocaltimestamp();
 		}
+		functionFactory.trunc();
+		functionFactory.dateTrunc();
 		functionFactory.bitLength();
 		functionFactory.octetLength();
 		functionFactory.ascii();

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

@@ -216,6 +216,7 @@ public void initializeFunctionRegistry(QueryEngine queryEngine) {
 		functionFactory.bitand();
 		functionFactory.lastDay();
 		functionFactory.toCharNumberDateTimestamp();
+		functionFactory.dateTrunc_trunc();
 		functionFactory.ceiling_ceil();
 		functionFactory.concat_pipeOperator();
 		functionFactory.rownumRowid();

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

@@ -2448,4 +2448,13 @@ public void dateTrunc() {
 				.register();
 	}
 
+	public void dateTrunc_trunc() {
+		functionRegistry.patternDescriptorBuilder( "date_trunc", "trunc(?2,'?1')" )
+				.setInvariantType(timestampType)
+				.setExactArgumentCount( 2 )
+				.setParameterTypes(TEMPORAL_UNIT, TEMPORAL)
+				.setArgumentListSignature( "(TEMPORAL_UNIT field, TEMPORAL datetime)" )
+				.register();
+	}
+
 }

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

@@ -8,10 +8,16 @@
 
 import org.hibernate.QueryException;
 import org.hibernate.dialect.CockroachDialect;
+import org.hibernate.dialect.DB2Dialect;
 import org.hibernate.dialect.DerbyDialect;
 
+import org.hibernate.dialect.H2Dialect;
 import org.hibernate.dialect.MariaDBDialect;
 import org.hibernate.dialect.MySQLDialect;
+import org.hibernate.dialect.OracleDialect;
+import org.hibernate.dialect.PostgreSQLDialect;
+import org.hibernate.dialect.SQLServerDialect;
+import org.hibernate.dialect.SybaseDialect;
 import org.hibernate.dialect.TiDBDialect;
 
 import org.hibernate.testing.TestForIssue;
@@ -473,6 +479,46 @@ public void testMathFunctions(SessionFactoryScope scope) {
 		);
 	}
 
+	@Test
+	@SkipForDialect(dialectClass = MySQLDialect.class, matchSubTypes = true)
+	@SkipForDialect(dialectClass = SQLServerDialect.class)
+	@SkipForDialect(dialectClass = SybaseDialect.class, matchSubTypes = true)
+	@SkipForDialect(dialectClass = DerbyDialect.class)
+	public void testTruncFunction(SessionFactoryScope scope) {
+		scope.inTransaction(
+				session -> {
+					assertThat( session.createQuery("select trunc(32.92345)").getSingleResult(), is(32d) );
+					assertThat( session.createQuery("select trunc(32.92345,3)").getSingleResult(), is(32.923d) );
+				}
+		);
+	}
+
+	@Test
+	@RequiresDialect(MySQLDialect.class)
+	@RequiresDialect(SQLServerDialect.class)
+	@RequiresDialect(DB2Dialect.class)
+	@RequiresDialect(H2Dialect.class)
+	public void testTruncateFunction(SessionFactoryScope scope) {
+		scope.inTransaction(
+				session -> {
+					assertThat( session.createQuery("select truncate(32.92345,3)").getSingleResult(), is(32.923d) );
+				}
+		);
+	}
+
+	@Test
+	@RequiresDialect(H2Dialect.class)
+	@RequiresDialect(DB2Dialect.class)
+	@RequiresDialect(OracleDialect.class)
+	@RequiresDialect(PostgreSQLDialect.class)
+	public void testDateTruncFunction(SessionFactoryScope scope) {
+		scope.inTransaction(
+				session -> {
+					session.createQuery("select date_trunc(year,current_timestamp)").getSingleResult();
+				}
+		);
+	}
+
 	@Test
 	public void testLowerUpperFunctions(SessionFactoryScope scope) {
 		scope.inTransaction(