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

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2018 IBM Corporation and others.
+ * Copyright (c) 2000, 2025 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -33,6 +33,9 @@
 import org.eclipse.swt.widgets.Display;
 
 import org.eclipse.core.runtime.Assert;
+import org.eclipse.core.runtime.ILog;
+import org.eclipse.core.runtime.IStatus;
+import org.eclipse.core.runtime.Status;
 
 import org.eclipse.jface.internal.text.SelectionProcessor;
 
@@ -272,6 +275,32 @@ 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) {
+				return;
+			}
+			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;
+
 
 	/**
 	 * Creates a new projection source viewer.
@@ -313,6 +349,7 @@ private void computeExpectedExecutionCosts() {
 	 */
 	public ProjectionViewer(Composite parent, IVerticalRuler ruler, IOverviewRuler overviewRuler, boolean showsAnnotationOverview, int styles) {
 		super(parent, ruler, overviewRuler, showsAnnotationOverview, styles);
+		fUpdateDocumentListener= new UpdateDocumentListener();
 	}
 
 	/**
@@ -510,6 +547,14 @@ public final void disableProjection() {
 			fProjectionAnnotationModel.removeAllAnnotations();
 			fFindReplaceDocumentAdapter= null;
 			fireProjectionDisabled();
+			if (fVisibleRegionDuringProjection != null) {
+				super.setVisibleRegion(fVisibleRegionDuringProjection.getOffset(), fVisibleRegionDuringProjection.getLength());
+				fVisibleRegionDuringProjection= null;
+			}
+			IDocument document= getDocument();
+			if (document != null) {
+				document.removeDocumentListener(fUpdateDocumentListener);
+			}
 		}
 	}
 
@@ -521,6 +566,15 @@ public final void enableProjection() {
 			addProjectionAnnotationModel(getVisualAnnotationModel());
 			fFindReplaceDocumentAdapter= null;
 			fireProjectionEnabled();
+			IDocument document= getDocument();
+			if (document == null) {
+				return;
+			}
+			IRegion visibleRegion= getVisibleRegion();
+			if (visibleRegion != null && (visibleRegion.getOffset() != 0 || visibleRegion.getLength() != 0) && visibleRegion.getLength() < document.getLength()) {
+				setVisibleRegion(visibleRegion.getOffset(), visibleRegion.getLength());
+			}
+			document.addDocumentListener(fUpdateDocumentListener);
 		}
 	}
 
@@ -529,6 +583,10 @@ 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 +741,70 @@ 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()) {
+			super.setVisibleRegion(start, length);
+			return;
+		}
+		IDocument document= getDocument();
+		if (document == null) {
+			return;
+		}
+		try {
+			// If the visible region changes, make sure collapsed regions outside of the old visible regions are expanded
+			// and collapse everything outside the new visible region
+			int end= computeEndOfVisibleRegion(start, length, document);
+			expandOutsideCurrentVisibleRegion(document);
+			collapseOutsideOfNewVisibleRegion(start, end, document);
+			fVisibleRegionDuringProjection= new Region(start, end - start - 1);
+		} catch (BadLocationException e) {
+			ILog log= ILog.of(getClass());
+			log.log(new Status(IStatus.WARNING, getClass(), IStatus.OK, null, e));
+		}
+	}
+
+	private void expandOutsideCurrentVisibleRegion(IDocument document) throws BadLocationException {
+		if (fVisibleRegionDuringProjection != null) {
+			expand(0, fVisibleRegionDuringProjection.getOffset(), false);
+			int oldEnd= fVisibleRegionDuringProjection.getOffset() + fVisibleRegionDuringProjection.getLength();
+			int length= document.getLength() - oldEnd;
+			if (length > 0) {
+				expand(oldEnd, length, false);
+			}
+		}
+	}
+
+	private void collapseOutsideOfNewVisibleRegion(int start, int end, IDocument document) throws BadLocationException {
+		int documentLength= document.getLength();
+		collapse(0, start, true);
+
+		int endInvisibleRegionLength= documentLength - end;
+		if (endInvisibleRegionLength > 0) {
+			collapse(end, endInvisibleRegionLength, true);
+		}
+	}
+
+	private static int computeEndOfVisibleRegion(int start, int length, IDocument document) throws BadLocationException {
+		int documentLength= document.getLength();
+		int end= start + length + 1;
+		// ensure that trailing whitespace is included
+		// In this case, the line break needs to be included as well
+		boolean visibleRegionEndsWithTrailingWhitespace= end < documentLength && isWhitespaceButNotNewline(document.getChar(end - 1));
+		while (end < documentLength && isWhitespaceButNotNewline(document.getChar(end))) {
+			end++;
+			visibleRegionEndsWithTrailingWhitespace= true;
+		}
+		if (visibleRegionEndsWithTrailingWhitespace && end < documentLength && isLineBreak(document.getChar(end))) {
+			end++;
+		}
+		return end;
+	}
+
+	private static boolean isWhitespaceButNotNewline(char c) {
+		return Character.isWhitespace(c) && !isLineBreak(c);
+	}
+
+	private static boolean isLineBreak(char c) {
+		return c == '\n' || c == '\r';
 	}
 
 	@Override
@@ -710,7 +829,9 @@ public void resetVisibleRegion() {
 
 	@Override
 	public IRegion getVisibleRegion() {
-		disableProjection();
+		if (fVisibleRegionDuringProjection != null) {
+			return fVisibleRegionDuringProjection;
+		}
 		IRegion visibleRegion= getModelCoverage();
 		if (visibleRegion == null)
 			visibleRegion= new Region(0, 0);