TextMergeView Unhandled IndexOutOfBoundsException at lines height calc

In the TextMergeViewer the method
getHeightBetweenLines(MergeSourceViewer tp, int fromLine, int toLine)
was be called with a higher toLine value than the number of lines in the
TextWidget. The reason was that there can be a document region offset,
which was not handled.
This can be checked with the example here:
#1542
which is the compare of java methods.
Solution: handle the document region offset before getHeightBetweenLines
will be called.
In getHeightBetweenLines we should prevent an index out of bounds
exception with a fallback logic. This could lead to wrong paintings, but
this is better than a RuntimeException.
Previously in the shift calculation also the document region offset was
handled. But now the heights of lines can be flexible, so this
calculation doesn't makes sense anymore for us.

Fixes #1536

Signed-off-by: Denis Ungemach <[email protected]>

Author: DenisUngemach

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java

@@ -2251,7 +2251,7 @@ private Diff handleMouseInSides(Canvas canvas, MergeSourceViewer tp, int my) {
 			return null;
 
 		if (fMerger.hasChanges()) {
-			int shift= tp.getVerticalScrollOffset() + (2-LW);
+			int shift = calculateShift(tp) + (2 - LW);
 
 			Point region= new Point(0, 0);
 			char leg = getLeg(tp);
@@ -2264,6 +2264,7 @@ private Diff handleMouseInSides(Canvas canvas, MergeSourceViewer tp, int my) {
 					continue;
 
 				tp.getLineRange(diff.getPosition(leg), region);
+				region.x -= tp.getDocumentRegionOffset();
 				int y = getHeightBetweenLines(tp, 0, region.x) + shift;
 				int h = getHeightBetweenLines(tp, region.x, region.x + region.y);
 
@@ -2293,8 +2294,8 @@ private Diff getDiffUnderMouse(Canvas canvas, int mx, int my, Rectangle r) {
 			return null;
 
 		if (fMerger.hasChanges()) {
-			int lshift= fLeft.getVerticalScrollOffset();
-			int rshift= fRight.getVerticalScrollOffset();
+			int lshift = calculateShift(fLeft);
+			int rshift = calculateShift(fRight);
 
 			Point region= new Point(0, 0);
 
@@ -2307,10 +2308,12 @@ private Diff getDiffUnderMouse(Canvas canvas, int mx, int my, Rectangle r) {
 					continue;
 
 				fLeft.getLineRange(diff.getPosition(LEFT_CONTRIBUTOR), region);
+				region.x -= fLeft.getDocumentRegionOffset();
 				int ly = getHeightBetweenLines(fLeft, 0, region.x) + lshift;
 				int lh = getHeightBetweenLines(fLeft, region.x, region.x + region.y);
 
 				fRight.getLineRange(diff.getPosition(RIGHT_CONTRIBUTOR), region);
+				region.x -= fRight.getDocumentRegionOffset();
 				int ry = getHeightBetweenLines(fRight, 0, region.x) + rshift;
 				int rh = getHeightBetweenLines(fRight, region.x, region.x + region.y);
 
@@ -4222,6 +4225,9 @@ private void updateLines(IDocument d) {
 	 * @return
 	 */
 	private int getHeightBetweenLines(MergeSourceViewer tp, int fromLine, int toLine) {
+
+		if (fromLine == toLine)
+			return 0;
 		StyledText w = tp.getSourceViewer().getTextWidget();
 		List<Integer> lineHeights = this.lineHeightsByViewer.get(tp);
 		if (lineHeights == null) {
@@ -4236,7 +4242,16 @@ private int getHeightBetweenLines(MergeSourceViewer tp, int fromLine, int toLine
 				}
 			});
 		}
+
 		int lineSpacing = w.getLineSpacing();
+
+		// If the linenumber is higher than the number of lines, we should prevent an
+		// IndexOutOfBoundsException
+		if (toLine > w.getLineCount()){
+			int lineHeight = tp.getSourceViewer().getTextWidget().getLineHeight();
+			return (toLine - fromLine) * (lineHeight + w.getLineVerticalIndent(0)) + lineSpacing;
+		}
+
 		int height = 0;
 		for (int i = fromLine; i < toLine; i++) {
 			Integer heightAtLine = lineHeights.get(i);
@@ -4317,8 +4332,8 @@ private void paintCenter(Canvas canvas, GC g) {
 			return;
 
 		if (fMerger.hasChanges()) {
-			int lshift= fLeft.getVerticalScrollOffset();
-			int rshift= fRight.getVerticalScrollOffset();
+			int lshift = calculateShift(fLeft);
+			int rshift = calculateShift(fRight);
 
 			Point region= new Point(0, 0);
 
@@ -4332,10 +4347,12 @@ private void paintCenter(Canvas canvas, GC g) {
 					continue;
 
 				fLeft.getLineRange(diff.getPosition(LEFT_CONTRIBUTOR), region);
+				region.x -= fLeft.getDocumentRegionOffset();
 				int ly = getHeightBetweenLines(fLeft, 0, region.x) + lshift;
 				int lh = getHeightBetweenLines(fLeft, region.x, region.x + region.y);
 
 				fRight.getLineRange(diff.getPosition(RIGHT_CONTRIBUTOR), region);
+				region.x -= fRight.getDocumentRegionOffset();
 				int ry = getHeightBetweenLines(fRight, 0, region.x) + rshift;
 				int rh = getHeightBetweenLines(fRight, region.x, region.x + region.y);
 
@@ -4436,6 +4453,10 @@ private void buildBaseCenterCurve(int w) {
 		}
 	}
 
+	private int calculateShift(MergeSourceViewer tp) {
+		return tp.getSourceViewer().getTopInset() - tp.getSourceViewer().getTextWidget().getTopPixel();
+	}
+
 	private void paintSides(GC g, MergeSourceViewer tp, Canvas canvas, boolean right) {
 
 		Display display= canvas.getDisplay();
@@ -4462,7 +4483,7 @@ private void paintSides(GC g, MergeSourceViewer tp, Canvas canvas, boolean right
 
 		if (fMerger.hasChanges()) {
 			boolean allOutgoing = allOutgoing();
-			int shift= tp.getVerticalScrollOffset() + (2-LW);
+			int shift = calculateShift(tp) + (2 - LW);
 
 			Point region= new Point(0, 0);
 			char leg = getLeg(tp);
@@ -4475,6 +4496,7 @@ private void paintSides(GC g, MergeSourceViewer tp, Canvas canvas, boolean right
 					continue;
 
 				tp.getLineRange(diff.getPosition(leg), region);
+				region.x -= tp.getDocumentRegionOffset();
 				int y = getHeightBetweenLines(tp, 0, region.x) + shift;
 				int h = getHeightBetweenLines(tp, region.x, region.x + region.y);
 
@@ -4522,7 +4544,7 @@ private void paint(PaintEvent event, MergeSourceViewer tp) {
 		Display display= canvas.getDisplay();
 
 		int w= canvas.getSize().x;
-		int shift= tp.getVerticalScrollOffset() + (2-LW);
+		int shift = calculateShift(tp) + (2 - LW);
 		int maxh= event.y+event.height; 	// visibleHeight
 
 		shift += fTopInset;
@@ -4540,6 +4562,7 @@ private void paint(PaintEvent event, MergeSourceViewer tp) {
 				continue;
 
 			tp.getLineRange(diff.getPosition(leg), range);
+			range.x -= tp.getDocumentRegionOffset();
 			int y = getHeightBetweenLines(tp, 0, range.x) + shift;
 			int h = getHeightBetweenLines(tp, range.x, range.x + range.y);