Ensure the last line is included in projection-based visible regions

This change ensures that setting the visible region with projections
enabled does not hide the last line in case there is additional text at
the end of the line or the file is using Windows line endings.

Author: danthe1st

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

@@ -841,24 +841,20 @@ private void collapseOutsideOfNewVisibleRegion(int start, int end, IDocument doc
 
 	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))) {
+		int end= start + length;
+		// ensure that the last line is fully included because projections cannot include partial lines
+		while (end < documentLength && !isLineBreak(document.getChar(end))) {
 			end++;
-			visibleRegionEndsWithTrailingWhitespace= true;
 		}
-		if (visibleRegionEndsWithTrailingWhitespace && end < documentLength && isLineBreak(document.getChar(end))) {
+		if (end < documentLength) {
+			end++;
+		}
+		if (end < documentLength && document.getChar(end) == '\n' && document.getChar(end - 1) == '\r') {
 			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';
 	}

tests/org.eclipse.jface.text.tests/src/org/eclipse/jface/text/tests/ProjectionViewerTest.java

@@ -16,6 +16,8 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.dnd.Clipboard;
@@ -516,4 +518,69 @@ private ProjectionAnnotation addVisibleRegionAndProjection(TestProjectionViewer
 		viewer.getProjectionAnnotationModel().addAnnotation(annotation, new Position(projectionStart, projectionEnd - projectionStart));
 		return annotation;
 	}
+
+	@ParameterizedTest
+	@CsvSource({ "true", "false" })
+	void testDifferentLineEndings(boolean crlf) {
+		Shell shell= new Shell(Display.getCurrent());
+		shell.setLayout(new FillLayout());
+		TestProjectionViewer viewer= new TestProjectionViewer(shell, null, null, true, SWT.ALL);
+		String documentContent= """
+				// before
+				{
+					// within
+				}
+				// after
+				""";
+		if (crlf) {
+			documentContent= documentContent.replace("\n", "\r\n");
+		}
+		Document document= new Document(documentContent);
+		viewer.setDocument(document, new AnnotationModel());
+		int start= documentContent.indexOf('{');
+		int end= documentContent.indexOf('}') + 1;
+		viewer.enableProjection();
+		viewer.setVisibleRegion(start, end - start);
+		assertEquals(documentContent.substring(start, documentContent.indexOf("// after")), viewer.getVisibleDocument().get());
+	}
+
+	@Test
+	void testIncludesLastLineIfAdditionalTextPresent() {
+		Shell shell= new Shell(Display.getCurrent());
+		shell.setLayout(new FillLayout());
+		TestProjectionViewer viewer= new TestProjectionViewer(shell, null, null, true, SWT.ALL);
+		String documentContent= """
+				// before
+				{
+					// within
+				}// ...
+				// should be hidden
+				""";
+		Document document= new Document(documentContent);
+		viewer.setDocument(document, new AnnotationModel());
+		int start= documentContent.indexOf('{');
+		int end= documentContent.indexOf('}') + 1;
+		viewer.enableProjection();
+		viewer.setVisibleRegion(start, end - start);
+		assertEquals(documentContent.substring(start, documentContent.indexOf("// should be hidden")), viewer.getVisibleDocument().get());
+	}
+
+	@Test
+	void testSetVisibleRegionUntilEOF() {
+		Shell shell= new Shell(Display.getCurrent());
+		shell.setLayout(new FillLayout());
+		TestProjectionViewer viewer= new TestProjectionViewer(shell, null, null, true, SWT.ALL);
+		String documentContent= """
+				// before
+				{
+					// within
+				}""";
+		Document document= new Document(documentContent);
+		viewer.setDocument(document, new AnnotationModel());
+		int start= documentContent.indexOf('{');
+		int end= documentContent.indexOf('}') + 1;
+		viewer.enableProjection();
+		viewer.setVisibleRegion(start, end - start);
+		assertEquals(documentContent.substring(start), viewer.getVisibleDocument().get());
+	}
 }