Bug 536952 - Avoid QuickDiff re-enabling in DocumentRewriteSessionEvent

* Only resume the DocumentLineDiffer if if was previously suspended by a
DocumentRewriteSessionEvent.
* Add a null check at
AbstractDocument.stopRewriteSession(DocumentRewriteSession) to avoid a
NullPointerException if startRewriteSession is not called before calling
stopRewriteSession. The javadoc of stopRewriteSession says "This method
has only any effect if startRewriteSession has been called before.",
without the null-check the method had an effect if startRewriteSession
was not called before, namely an NPE.

Change-Id: Ia6f92c686c934e1c7cbb514e2c32ac055b557935
Signed-off-by: Etienne Reichenbach <etienner@gmail.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/texteditor/quickdiff/DocumentLineDiffer.java b/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/texteditor/quickdiff/DocumentLineDiffer.java
index ac12e9cc0d2..5ab2dafd55e 100644
--- a/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/texteditor/quickdiff/DocumentLineDiffer.java
+++ b/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/texteditor/quickdiff/DocumentLineDiffer.java
@@ -213,14 +213,30 @@ public class DocumentLineDiffer implements ILineDiffer, IDocumentListener, IAnno
 	 * @since 3.2
 	 */
 	private final IDocumentRewriteSessionListener fSessionListener= new IDocumentRewriteSessionListener() {
+
+		/**
+		 * <code>true</code> if this line differ was suspended because of a
+		 * {@link DocumentRewriteSessionEvent#SESSION_START session start} and
+		 * needs to be resumed after a
+		 * {@link DocumentRewriteSessionEvent#SESSION_STOP session stop} event,
+		 * <code>false</code> otherwise.
+		 */
+		private boolean fResumeOnRewriteSessionStop;
+
 		@Override
 		public void documentRewriteSessionChanged(DocumentRewriteSessionEvent event) {
 			if (event.getSession().getSessionType() == DocumentRewriteSessionType.UNRESTRICTED_SMALL)
 				return;
-			if (DocumentRewriteSessionEvent.SESSION_START.equals(event.getChangeType()))
+			if (DocumentRewriteSessionEvent.SESSION_START.equals(event.getChangeType())) {
+				fResumeOnRewriteSessionStop = !isSuspended();
 				suspend();
-			else if (DocumentRewriteSessionEvent.SESSION_STOP.equals(event.getChangeType()))
+			}
+			else if (fResumeOnRewriteSessionStop
+					&& DocumentRewriteSessionEvent.SESSION_STOP.equals(event.getChangeType())) {
 				resume();
+				fResumeOnRewriteSessionStop= false;
+			}
+
 		}
 	};