@danthe1st WDYT?

Test Results

 3 015 files  ±0   3 015 suites  ±0   2h 15m 33s ⏱️ - 6m 47s
 8 266 tests ±0   8 018 ✅ +1  248 💤 ±0  0 ❌  - 1 
23 622 runs  ±0  22 831 ✅ +1  791 💤 ±0  0 ❌  - 1 

Results for commit 0009523. ± Comparison against base commit 3d42a70.

@danthe1st WDYT?

I think it looks good as a bugfix in general but I think it would make sense to do more.
If the selected end is directly after the line break, I guess it doesn't really make sense to include the last line as well so I guess something like the following might make more sense:

		if (length == 0 || isLineBreak(document.getChar(end - 1))) {
			return end + 1;
		}

That could be tested as follows (the test in this example is parameterized to show that the result is the same both with and without projections):

	@ParameterizedTest
	@CsvSource({ "true", "false" })
	void testEndWithStartOfLine(boolean enableProjections) {
		Shell shell= new Shell();
		shell.setLayout(new FillLayout());
		TestProjectionViewer viewer= new TestProjectionViewer(shell, null, null, false, SWT.NONE);
		String documentContent= """
				Hello
				World
				123
				456
				""";
		Document document= new Document(documentContent);
		viewer.setDocument(document, new AnnotationModel());
		if (enableProjections) {
			viewer.enableProjection();
		}

		viewer.setVisibleRegion(documentContent.indexOf("World"), documentContent.indexOf("123") - documentContent.indexOf("World"));
		shell.setVisible(true);
		try {
			assertEquals("World\n", viewer.getVisibleDocument().get());
		} finally {
			shell.dispose();
		}
	}

I also ran some relevant tests I know in other projects (org.eclipse.xtend.ide.tests.autoedit.AutoEditTest in xtext, FoldingTestSuite in JDT-UI, DocumentLinkReconcilingTest in lsp4e) and at least they don't seem to break either.

@danthe1st can you push a new PR for your suggestion (or update mine, not sure if that will work)?

@danthe1st can you push a new PR for your suggestion (or update mine, not sure if that will work)?

I can't update your PR but I created #3671