avoid STDERR diff3 messages when using wfMerge()

diff3 issues a warning to stderr if any of the files does not end with a
newline character.

TextContent::preSaveTransform() does normalize revision text by simply
calling trim().  Thus to avoid a diff3 error we simply apply the same
normalization and add a newline to please the command.

Change-Id: I7baa3df95dd70cbc865b2491ccc791e60f8b9e6e

includes/GlobalFunctions.php

@@ -2895,11 +2895,15 @@ function wfMerge( $old, $mine, $yours, &$result ) {
 	$mytextFile = fopen( $mytextName = tempnam( $td, 'merge-mine-' ), 'w' );
 	$yourtextFile = fopen( $yourtextName = tempnam( $td, 'merge-your-' ), 'w' );
 
-	fwrite( $oldtextFile, $old );
+	# NOTE: diff3 issues a warning to stderr if any of the files does not end with
+	#       a newline character. To avoid this, we normalize the trailing whitespace before
+	#       creating the diff.
+
+	fwrite( $oldtextFile, rtrim( $old ) . "\n" );
 	fclose( $oldtextFile );
-	fwrite( $mytextFile, $mine );
+	fwrite( $mytextFile, rtrim( $mine ) . "\n" );
 	fclose( $mytextFile );
-	fwrite( $yourtextFile, $yours );
+	fwrite( $yourtextFile, rtrim( $yours ) . "\n" );
 	fclose( $yourtextFile );
 
 	# Check for a conflict

tests/phpunit/includes/GlobalFunctions/GlobalTest.php

@@ -488,6 +488,86 @@ class GlobalTest extends MediaWikiTestCase {
 		);
 	}
 
+	/**
+	 * @param String $old: Text as it was in the database
+	 * @param String $mine: Text submitted while user was editing
+	 * @param String $yours: Text submitted by the user
+	 * @param Boolean $expectedMergeResult Whether the merge should be a success
+	 * @param String $expectedText: Text after merge has been completed
+	 *
+	 * @dataProvider provideMerge()
+	 */
+	public function testMerge( $old, $mine, $yours, $expectedMergeResult, $expectedText ) {
+		$mergedText = null;
+		$isMerged = wfMerge( $old, $mine, $yours, $mergedText );
+
+		$msg = 'Merge should be a ';
+		$msg .= $expectedMergeResult ? 'success' : 'failure';
+		$this->assertEquals( $expectedMergeResult, $isMerged, $msg );
+
+		if( $isMerged ) {
+			// Verify the merged text
+			$this->assertEquals( $expectedText, $mergedText,
+				'is merged text as expected?' );
+		}
+	}
+
+	public static function provideMerge() {
+		$EXPECT_MERGE_SUCCESS = true;
+		$EXPECT_MERGE_FAILURE = false;
+
+		return array(
+
+			// #0: clean merge
+			array(
+				// old:
+				"one one one\n" . // trimmed
+				"\n" .
+				"two two two",
+
+				// mine:
+				"one one one ONE ONE\n" .
+				"\n" .
+				"two two two\n", // with tailing whitespace
+
+				// yours:
+				"one one one\n" .
+				"\n" .
+				"two two TWO TWO", // trimmed
+
+				// ok:
+				$EXPECT_MERGE_SUCCESS,
+
+				// result:
+				"one one one ONE ONE\n" .
+				"\n" .
+				"two two TWO TWO\n", // note: will always end in a newline
+			),
+
+			// #1: conflict, fail
+			array(
+				// old:
+				"one one one", // trimmed
+
+				// mine:
+				"one one one ONE ONE\n" .
+				"\n" .
+				"bla bla\n" .
+				"\n", // with tailing whitespace
+
+				// yours:
+				"one one one\n" .
+				"\n" .
+				"two two", // trimmed
+
+				$EXPECT_MERGE_FAILURE,
+
+				// result:
+				null,
+			),
+		);
+	}
+
 	/**
 	 * @dataProvider provideMakeUrlIndexes()
 	 */