From c9f41dc9b7de2aed1633c28b22597181a5cdd38b Mon Sep 17 00:00:00 2001
From: Sanne Grinovero <sanne@hibernate.org>
Date: Thu, 1 Aug 2019 12:23:05 +0100
Subject: [PATCH] HHH-13512 Avoid allocating an array in
 org.hibernate.internal.util.StringHelper#unquote(String[], Dialect) if there
 are no changes to be applied

---
 .../hibernate/internal/util/StringHelper.java | 27 +++++++++++++----
 .../hibernate/test/util/StringHelperTest.java | 29 +++++++++++++++++++
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java b/hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java
index c3a8ad0aee..e9d56cd264 100644
--- a/hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java
+++ b/hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java
@@ -736,15 +736,32 @@ public final class StringHelper {
 	 *
 	 * @return The unquoted versions.
 	 */
-	public static String[] unquote(String[] names, Dialect dialect) {
+	public static String[] unquote(final String[] names, final Dialect dialect) {
 		if ( names == null ) {
 			return null;
 		}
-		String[] unquoted = new String[names.length];
-		for ( int i = 0; i < names.length; i++ ) {
-			unquoted[i] = unquote( names[i], dialect );
+		int failedIndex = -1;
+		final int length = names.length;
+		for ( int i = 0; i < length; i++ ) {
+			if ( isQuoted( names[i], dialect ) ) {
+				failedIndex = i;
+				break;
+			}
+		}
+		if ( failedIndex == -1 ) {
+			//In this case all strings are already unquoted, so return the same array as the input:
+			//this is a good optimisation to skip an array copy as typically either all names are consistently quoted, or none are;
+			//yet for safety we need to deal with mixed scenarios as well.
+			return names;
+		}
+		else {
+			String[] unquoted = new String[length];
+			System.arraycopy( names, 0, unquoted, 0, failedIndex );
+			for ( int i = failedIndex; i < length; i++ ) {
+				unquoted[i] = unquote( names[i], dialect );
+			}
+			return unquoted;
 		}
-		return unquoted;
 	}
 
 
diff --git a/hibernate-core/src/test/java/org/hibernate/test/util/StringHelperTest.java b/hibernate-core/src/test/java/org/hibernate/test/util/StringHelperTest.java
index bec3ebef07..f3009a6b88 100644
--- a/hibernate-core/src/test/java/org/hibernate/test/util/StringHelperTest.java
+++ b/hibernate-core/src/test/java/org/hibernate/test/util/StringHelperTest.java
@@ -6,18 +6,24 @@
  */
 package org.hibernate.test.util;
 
+import java.util.Arrays;
+
+import org.junit.Assert;
 import org.junit.Test;
 
+import org.hibernate.dialect.H2Dialect;
 import org.hibernate.internal.util.StringHelper;
 import org.hibernate.testing.junit4.BaseUnitTestCase;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 /**
  * @author Steve Ebersole
  */
 public class StringHelperTest extends BaseUnitTestCase {
+
 	private static final String BASE_PACKAGE = "org.hibernate";
 	private static final String STRING_HELPER_FQN = "org.hibernate.internal.util.StringHelper";
 	private static final String STRING_HELPER_NAME = StringHelper.unqualify( STRING_HELPER_FQN );
@@ -54,4 +60,27 @@ public class StringHelperTest extends BaseUnitTestCase {
 		assertEquals( StringHelper.indexOfIdentifierWord( "no identifier here", "?1" ), -1 );
 		assertEquals( StringHelper.indexOfIdentifierWord( "some text ?", "?" ), 10 );
 	}
+
+	private static H2Dialect DIALECT = new H2Dialect();
+	@Test
+	public void testArrayUnquoting() {
+		assertNull( StringHelper.unquote( (String[]) null, DIALECT ) );
+		//This to verify that the string array isn't being copied unnecessarily:
+		unchanged( new String [0] );
+		unchanged( new String[] { "a" } );
+		unchanged( new String[] { "a", "b" } );
+		helperEquals( new String[] { "a", "b", "c" }, new String[] { "a", "b", "`c`" } );
+		helperEquals( new String[] { "a", "b", "c" }, new String[] { "a", "\"b\"", "c" } );
+	}
+
+	private static void unchanged(String[] input) {
+		final String[] output = StringHelper.unquote( input, DIALECT );
+		assertTrue( input == output );
+	}
+
+	private static void helperEquals(String[] expectation, String[] input) {
+		final String[] output = StringHelper.unquote( input, DIALECT );
+		assertTrue( Arrays.equals( expectation, output ) );
+	}
+
 }