Bug 515500: Preserve known line numbers when updating ui

This resolves a significant UI performance regression so
now line numbers don't need to be recalculated for areas
where they are already known.

Change-Id: I4668d620cde24b7cd8c6a22e9c022eaf5b237ff2
(cherry picked from commit 679896ec6e)

core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/buildconsole/BuildConsolePartitionerEditDataTest.java

@@ -53,24 +53,30 @@ public class BuildConsolePartitionerEditDataTest {
 		assertThat(update0.getNewContents(), is(""));
 		assertThat(update0.getStreamsNeedingNotifcation(), is(empty()));
 		assertThat(update0.needsClearDocumentMarkerManager(), is(true));
+		assertThat(update0.getOffset(), is(0L));
 
 		data.append("Line of text\n", stream1, null);
 		UpdateUIData update1 = data.getUpdate();
 		assertThat(update1.getNewContents(), is("Line of text\n"));
 		assertThat(update1.getStreamsNeedingNotifcation(), is(Arrays.asList(stream1)));
 		assertThat(update1.needsClearDocumentMarkerManager(), is(false));
+		assertThat(update1.getOffset(), is(0L));
 
 		data.append("Another line of text\n", stream2, null);
 		UpdateUIData update2 = data.getUpdate();
 		assertThat(update2.getNewContents(), is("Line of text\nAnother line of text\n"));
 		assertThat(update2.getStreamsNeedingNotifcation(), is(Arrays.asList(stream2)));
 		assertThat(update2.needsClearDocumentMarkerManager(), is(false));
+		assertThat(update2.getOffset(), is(0L));
 	}
 
 	@Test
 	public void testOverflow() {
+		StringBuilder all = new StringBuilder();
 		for (int i = 0; i < DEFAULT_MAX_LINES * 4; i++) {
-			data.append("Line " + i + "\n", stream1, null);
+			String text = "Line " + i + "\n";
+			data.append(text, stream1, null);
+			all.append(text);
 		}
 
 		UpdateUIData update = data.getUpdate();
@@ -86,6 +92,9 @@ public class BuildConsolePartitionerEditDataTest {
 		assertThat(contents, endsWith("Line " + lastLine + "\n"));
 		int firstLine = lastLine - newlines + 1;
 		assertThat(contents, startsWith("Line " + firstLine + "\n"));
+
+		long expectedOffset = all.indexOf(contents);
+		assertThat(update.getOffset(), is(expectedOffset));
 	}
 
 	@Test

core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/buildconsole/BuildConsolePartitioner.java

@@ -26,6 +26,7 @@ import org.eclipse.core.filesystem.EFS;
 import org.eclipse.core.filesystem.IFileStore;
 import org.eclipse.core.resources.IProject;
 import org.eclipse.core.runtime.CoreException;
+import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IDocumentPartitioner;
@@ -104,6 +105,8 @@ public class BuildConsolePartitioner
 
 	private int fUpdateDelay = BuildConsolePreferencePage.DEFAULT_BUILDCONSOLE_UPDATE_DELAY_MS;
 
+	private long fOffset;
+
 	/**
 	 * Construct a partitioner that is not associated with a specific project
 	 */
@@ -251,19 +254,23 @@ public class BuildConsolePartitioner
 			fDocumentMarkerManager.clear();
 		}
 
-		/*
-		 * This call is slow, it updates the UI as a side effect.
-		 *
-		 * XXX: Doing a set on the whole document means that all the line
-		 * numbers need to be recalculated. This can be optimized further by
-		 * keeping track of what needs to be edited. However, for now this
-		 * optimization has not been done because although this leads to
-		 * increased CPU usage, it does not lead to a delay in total processing
-		 * time, but rather to a decrease in frame rate. Furthermore, if the
-		 * document overflows, the document's line numbers need to be
-		 * recalculated anyway, so little benefit.
-		 */
-		fDocument.set(update.getNewContents());
+		try {
+			long offsetChangeSinceLastUpdate = update.getOffset() - fOffset;
+			int toTrim = (int) Math.min(offsetChangeSinceLastUpdate, fDocument.getLength());
+
+			int length = fDocument.getLength();
+			String newContents = update.getNewContents();
+			String appendContents = newContents.substring(length - toTrim);
+			// The append has to be done before the delete from head
+			// to avoid document becoming 0 length and therefore the
+			// listeners assume the document has been cleared
+			fDocument.replace(length + toTrim, 0, appendContents);
+			fDocument.replace(0, toTrim, ""); //$NON-NLS-1$
+		} catch (BadLocationException e) {
+			fDocument.set(update.getNewContents());
+		}
+
+		fOffset = update.getOffset();
 	}
 
 	/**

core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/buildconsole/BuildConsolePartitionerEditData.java

@@ -36,6 +36,11 @@ public class BuildConsolePartitionerEditData {
 		 */
 		boolean needsClearDocumentMarkerManager();
 
+		/**
+		 * The content's offset since beginning of time.
+		 */
+		long getOffset();
+
 		/**
 		 * New contents for the build console.
 		 */
@@ -70,6 +75,11 @@ public class BuildConsolePartitionerEditData {
 	 */
 	private boolean fClearDocumentMarkerManager = false;
 
+	/**
+	 * Offset of the start of the document since the beginning of time.
+	 */
+	private long fOffset = 0;
+
 	/**
 	 * Editable document, all modifications are made to this copy of the
 	 * document, then the UI thread occasionally gets these updates
@@ -86,6 +96,7 @@ public class BuildConsolePartitionerEditData {
 	 */
 	private Set<IBuildConsoleStreamDecorator> fEditStreams = new HashSet<>();
 
+
 	public BuildConsolePartitionerEditData(int maxLines) {
 		fMaxLines = maxLines;
 	}
@@ -105,6 +116,7 @@ public class BuildConsolePartitionerEditData {
 		synchronized (this) {
 			fEditPartitions.clear();
 			fClearDocumentMarkerManager = true;
+			fOffset += fEditStringBuilder.length();
 			fEditStringBuilder.setLength(0);
 			fEditLineCount = 0;
 		}
@@ -239,6 +251,7 @@ public class BuildConsolePartitionerEditData {
 			fEditPartitions = newParitions;
 			fClearDocumentMarkerManager = true;
 
+			fOffset += offsetToOffset;
 			fEditStringBuilder.delete(0, offsetToOffset);
 			fEditLineCount = newNewlineCount;
 
@@ -287,11 +300,13 @@ public class BuildConsolePartitionerEditData {
 	 */
 	public UpdateUIData getUpdate() {
 		boolean clearDocumentMarkerManager;
+		long newOffset;
 		String newConents;
 		List<ITypedRegion> newPartitions;
 		List<IBuildConsoleStreamDecorator> streamsNeedingNotifcation;
 
 		synchronized (this) {
+			newOffset = fOffset;
 			newConents = fEditStringBuilder.toString();
 			newPartitions = new ArrayList<>(fEditPartitions);
 			clearDocumentMarkerManager = fClearDocumentMarkerManager;
@@ -321,6 +336,11 @@ public class BuildConsolePartitionerEditData {
 			public String getNewContents() {
 				return newConents;
 			}
+
+			@Override
+			public long getOffset() {
+				return newOffset;
+			}
 		};
 	}