Allow using visible regions with projections eclipse-platform#3073

While ProjectionViewer supports both using visible regions and
projections, these features cannot be used in conjunction. This change
allows the use of projections when visible regions are used.

Fixes eclipse-platform#3074

Author: danthe1st

bundles/org.eclipse.jface.text/projection/org/eclipse/jface/text/source/projection/ProjectionViewer.java

@@ -99,6 +99,7 @@ public class ProjectionViewer extends SourceViewer implements ITextViewerExtensi
 	 */
 	public static final int COLLAPSE_ALL= BASE + 5;
 
+
 	/**
 	 * Internal listener to changes of the annotation model.
 	 */
@@ -272,6 +273,34 @@ private void computeExpectedExecutionCosts() {
 		}
 	}
 
+	/**
+	 * An {@link IDocumentListener} that makes sure that {@link #fVisibleRegionDuringProjection} is
+	 * updated when the document changes and ensures that the collapsed region after the visible
+	 * region is recreated appropriately.
+	 */
+	private final class UpdateDocumentListener implements IDocumentListener {
+		@Override
+		public void documentChanged(DocumentEvent event) {
+			if (fVisibleRegionDuringProjection != null) {
+				int oldLength= event.getLength();
+				int newLength= event.getText().length();
+				int oldVisibleRegionEnd= fVisibleRegionDuringProjection.getOffset() + fVisibleRegionDuringProjection.getLength();
+
+				if (event.getOffset() < fVisibleRegionDuringProjection.getOffset()) {
+					fVisibleRegionDuringProjection= new Region(fVisibleRegionDuringProjection.getOffset() + newLength - oldLength, fVisibleRegionDuringProjection.getLength());
+				} else {
+					if (event.getOffset() + oldLength < oldVisibleRegionEnd) {
+						fVisibleRegionDuringProjection= new Region(fVisibleRegionDuringProjection.getOffset(), fVisibleRegionDuringProjection.getLength() + newLength - oldLength);
+					}
+				}
+			}
+		}
+
+		@Override
+		public void documentAboutToBeChanged(DocumentEvent event) {
+		}
+	}
+
 	/** The projection annotation model used by this viewer. */
 	private ProjectionAnnotationModel fProjectionAnnotationModel;
 	/** The annotation model listener */
@@ -292,6 +321,11 @@ private void computeExpectedExecutionCosts() {
 	private IDocument fReplaceVisibleDocumentExecutionTrigger;
 	/** <code>true</code> if projection was on the last time we switched to segmented mode. */
 	private boolean fWasProjectionEnabled;
+	/**
+	 * The region set by {@link #setVisibleRegion(int, int)} during projection or <code>null</code>
+	 * if not in a projection
+	 */
+	private IRegion fVisibleRegionDuringProjection;
 	/** The queue of projection commands used to assess the costs of projection changes. */
 	private ProjectionCommandQueue fCommandQueue;
 	/**
@@ -301,6 +335,8 @@ private void computeExpectedExecutionCosts() {
 	 */
 	private int fDeletedLines;
 
+	private UpdateDocumentListener fUpdateDocumentListener= new UpdateDocumentListener();
+
 
 	/**
 	 * Creates a new projection source viewer.
@@ -510,6 +546,11 @@ public final void disableProjection() {
 			fProjectionAnnotationModel.removeAllAnnotations();
 			fFindReplaceDocumentAdapter= null;
 			fireProjectionDisabled();
+			if (fVisibleRegionDuringProjection != null) {
+				super.setVisibleRegion(fVisibleRegionDuringProjection.getOffset(), fVisibleRegionDuringProjection.getLength());
+				fVisibleRegionDuringProjection= null;
+			}
+			getDocument().removeDocumentListener(fUpdateDocumentListener);
 		}
 	}
 
@@ -518,9 +559,14 @@ public final void disableProjection() {
 	 */
 	public final void enableProjection() {
 		if (!isProjectionMode()) {
+			IRegion visibleRegion= getVisibleRegion();
 			addProjectionAnnotationModel(getVisualAnnotationModel());
 			fFindReplaceDocumentAdapter= null;
 			fireProjectionEnabled();
+			if (visibleRegion != null && (visibleRegion.getOffset() != 0 || visibleRegion.getLength() != 0) && visibleRegion.getLength() < getDocument().getLength()) {
+				setVisibleRegion(visibleRegion.getOffset(), visibleRegion.getLength());
+			}
+			getDocument().addDocumentListener(fUpdateDocumentListener);
 		}
 	}
 
@@ -529,6 +575,10 @@ private void expandAll() {
 		IDocument doc= getDocument();
 		int length= doc == null ? 0 : doc.getLength();
 		if (isProjectionMode()) {
+			if (fVisibleRegionDuringProjection != null) {
+				offset= fVisibleRegionDuringProjection.getOffset();
+				length= fVisibleRegionDuringProjection.getLength();
+			}
 			fProjectionAnnotationModel.expandAll(offset, length);
 		}
 	}
@@ -683,9 +733,48 @@ private int toLineStart(IDocument document, int offset, boolean testLastLine) th
 
 	@Override
 	public void setVisibleRegion(int start, int length) {
-		fWasProjectionEnabled= isProjectionMode();
-		disableProjection();
-		super.setVisibleRegion(start, length);
+		if (isProjectionMode()) {
+			try {
+				int documentLength= getDocument().getLength();
+				if (fVisibleRegionDuringProjection != null) {
+					expand(0, fVisibleRegionDuringProjection.getOffset(), false);
+					int oldEnd= fVisibleRegionDuringProjection.getOffset() + fVisibleRegionDuringProjection.getLength();
+					expand(oldEnd, documentLength - oldEnd, false);
+				}
+				collapse(0, start, true);
+
+				int end= start + length + 1;
+				// ensure that trailing whitespace is included
+				// In this case, the line break needs to be included as well
+				boolean movedDueToTrailingWhitespace= false;
+				while (end < documentLength && isWhitespaceButNotNewline(getDocument().getChar(end))) {
+					end++;
+					movedDueToTrailingWhitespace= true;
+				}
+				if (movedDueToTrailingWhitespace && end < documentLength && isLineBreak(getDocument().getChar(end))) {
+					end++;
+				}
+
+				int endInvisibleRegionLength= documentLength - end;
+				if (endInvisibleRegionLength > 0) {
+					collapse(end, endInvisibleRegionLength, true);
+				}
+				fVisibleRegionDuringProjection= new Region(start, end - start);
+			} catch (BadLocationException e) {
+				e.printStackTrace();
+			}
+			fVisibleRegionDuringProjection= new Region(start, length);
+		} else {
+			super.setVisibleRegion(start, length);
+		}
+	}
+
+	private boolean isWhitespaceButNotNewline(char c) {
+		return Character.isWhitespace(c) && !isLineBreak(c);
+	}
+
+	private boolean isLineBreak(char c) {
+		return c == '\n' || c == '\r';
 	}
 
 	@Override
@@ -710,6 +799,9 @@ public void resetVisibleRegion() {
 
 	@Override
 	public IRegion getVisibleRegion() {
+		if (fVisibleRegionDuringProjection != null) {
+			return fVisibleRegionDuringProjection;
+		}
 		disableProjection();
 		IRegion visibleRegion= getModelCoverage();
 		if (visibleRegion == null)