Fix sticky scroll height calculation for variable line heights

When emoji or other content affects line heights, sticky scroll was calculating the total height wrong by assuming all lines were the same. Now it gets the actual height for each line instead. Also fixes the height check for limiting visible lines.

Author: Christopher-Hermann

bundles/org.eclipse.ui.editors/src/org/eclipse/ui/internal/texteditor/stickyscroll/StickyScrollingControl.java

@@ -331,7 +331,10 @@ private void calculateAndSetStickyLinesCanvasBounds() {
 		StyledText textWidget= sourceViewer.getTextWidget();
 
 		int numberStickyLines= getNumberStickyLines();
-		int lineHeight= stickyLineText.getLineHeight() * numberStickyLines;
+		int lineHeight = 0;
+		for (int i = 0; i < numberStickyLines; i++) {
+			lineHeight += stickyLineText.getLineHeight(stickyLineText.getOffsetAtLine(i));
+		}
 		int spacingHeight= stickyLineText.getLineSpacing() * (numberStickyLines - 1);
 		int separatorHeight= bottomSeparator.getBounds().height;
 
@@ -450,7 +453,8 @@ private boolean areStickyLinesOutDated(StyledText textWidget) {
 	}
 
 	private void limitVisibleStickyLinesToTextWidgetHeight(StyledText textWidget) {
-		int lineHeight= textWidget.getLineHeight() + textWidget.getLineSpacing();
+		int topOffset = textWidget.getOffsetAtLine(textWidget.getTopIndex());
+		int lineHeight = textWidget.getLineHeight(topOffset) + textWidget.getLineSpacing();
 		int textWidgetHeight= textWidget.getBounds().height;
 
 		int visibleLinesInTextWidget= textWidgetHeight / lineHeight;

tests/org.eclipse.ui.editors.tests/src/org/eclipse/ui/internal/texteditor/stickyscroll/StickyScrollingControlTest.java

@@ -17,6 +17,7 @@
 import static org.hamcrest.Matchers.greaterThan;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -236,6 +237,33 @@ void testStyling() {
 		assertEquals(hoverColor, stickyLineText.getForeground());
 	}
 
+	@Test
+	void testCanvasBoundsHeightAdjustsForVariableLineHeights() {
+		sourceViewer.getTextWidget().setBounds(0, 0, 200, 200);
+
+		// Step 1: Set 2 plain-text sticky lines and record canvas height
+		List<IStickyLine> plainLines = List.of(new StickyLineStub("line 1", 0), new StickyLineStub("line 2", 1));
+		stickyScrollingControl.setStickyLines(plainLines);
+		Canvas stickyControlCanvas = getStickyControlCanvas(shell);
+		int heightWithPlainText = stickyControlCanvas.getBounds().height;
+
+		// Step 2: Replace second sticky line with line requiring space
+		Font largerFont = new Font(Display.getDefault(),
+				new FontData(shell.getFont().getFontData()[0].getName(), 40, SWT.NORMAL));
+		String bigText = "line 2 big"; //$NON-NLS-1$
+		StyleRange bigFontRange = new StyleRange(0, bigText.length(), null, null);
+		bigFontRange.font = largerFont;
+		List<IStickyLine> linesWithLargerFont = List.of(new StickyLineStub("line 1", 0),
+				new StickyLineStub(bigText, 1, new StyleRange[] { bigFontRange }));
+		stickyScrollingControl.setStickyLines(linesWithLargerFont);
+		int heightWithLargerFont = getStickyControlCanvas(shell).getBounds().height;
+
+		assertTrue(heightWithLargerFont > heightWithPlainText,
+				"Canvas height must increase when one sticky line has a larger font"); //$NON-NLS-1$
+
+		largerFont.dispose();
+	}
+
 	@Test
 	void testLayoutStickyLinesCanvasOnResize() {
 		sourceViewer.getTextWidget().setBounds(0, 0, 200, 200);