From 5d12274a22e123011d04c8d1d28c630d5c9c394f Mon Sep 17 00:00:00 2001
From: ammann <161159040+agammann@users.noreply.github.com>
Date: Sun, 11 Oct 2026 10:03:11 -0700
Subject: [PATCH] Fix line offsets when incremental edits join CRLF

---
 textDocument/src/main.ts                   |  8 +++++
 textDocument/src/test/textdocument.test.ts | 39 +++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/textDocument/src/main.ts b/textDocument/src/main.ts
index 06409de72..14dd59dbe 100644
--- a/textDocument/src/main.ts
+++ b/textDocument/src/main.ts
@@ -260,6 +260,14 @@ class FullTextDocument implements TextDocument {
 				const startOffset = this.offsetAt(range.start);
 				const endOffset = this.offsetAt(range.end);
 				this._content = this._content.substring(0, startOffset) + change.text + this._content.substring(endOffset, this._content.length);
+				const insertedEndOffset = startOffset + change.text.length;
+				const crlfAtStart = this._content.charCodeAt(startOffset - 1) === CharCode.CarriageReturn && this._content.charCodeAt(startOffset) === CharCode.LineFeed;
+				const crlfAtEnd = this._content.charCodeAt(insertedEndOffset - 1) === CharCode.CarriageReturn && this._content.charCodeAt(insertedEndOffset) === CharCode.LineFeed;
+				if (crlfAtStart || crlfAtEnd) {
+					// A CRLF pair across an edit boundary is not included in the inserted text's line offsets.
+					this._lineOffsets = undefined;
+					continue;
+				}
 
 				// update the offsets
 				const startLine = Math.max(range.start.line, 0);
diff --git a/textDocument/src/test/textdocument.test.ts b/textDocument/src/test/textdocument.test.ts
index 8aca2cac2..caeddfd67 100644
--- a/textDocument/src/test/textdocument.test.ts
+++ b/textDocument/src/test/textdocument.test.ts
@@ -339,6 +339,43 @@ suite('Text Document Full Updates', () => {
 });
 
 suite('Text Document Incremental Updates', () => {
+	test('Incremental edits that join CRLF across an edit boundary', () => {
+		const changes = [
+			{ original: 'a\rb', range: Ranges.create(1, 0, 1, 0), text: '\n' },
+			{ original: 'a\nb', range: Ranges.create(0, 1, 0, 1), text: '\r' },
+			{ original: 'a\rX\nb', range: Ranges.create(1, 0, 1, 1), text: '' }
+		];
+		const expected = newDocument('a\r\nb');
+
+		for (const change of changes) {
+			const document = newDocument(change.original);
+			TextDocument.update(document, [{ text: change.text, range: change.range }], 1);
+			assert.strictEqual(document.getText(), expected.getText());
+			assert.strictEqual(document.lineCount, expected.lineCount, change.original);
+			for (let offset = 0; offset <= document.getText().length; offset++) {
+				assert.deepStrictEqual(document.positionAt(offset), expected.positionAt(offset), change.original);
+			}
+			for (let line = 0; line < expected.lineCount; line++) {
+				assert.deepStrictEqual(document.getLineRange(line), expected.getLineRange(line), change.original);
+				assert.strictEqual(document.getEOLCharacters(line), expected.getEOLCharacters(line), change.original);
+				for (let character = 0; character <= 3; character++) {
+					assert.strictEqual(document.offsetAt(Positions.create(line, character)), expected.offsetAt(Positions.create(line, character)), change.original);
+				}
+			}
+		}
+
+		const batched = newDocument('a\rb');
+		TextDocument.update(batched, [
+			{ text: '\n', range: Ranges.create(1, 0, 1, 0) },
+			{ text: 'X', range: Ranges.create(1, 0, 1, 0) }
+		], 1);
+		const expectedBatch = newDocument('a\r\nXb');
+		assert.strictEqual(batched.getText(), expectedBatch.getText());
+		assert.strictEqual(batched.lineCount, expectedBatch.lineCount);
+		for (let offset = 0; offset <= batched.getText().length; offset++) {
+			assert.deepStrictEqual(batched.positionAt(offset), expectedBatch.positionAt(offset));
+		}
+	});
 
 	// assumes that only '\n' is used
 	function assertValidLineNumbers(doc: TextDocument) {
@@ -622,4 +659,4 @@ suite('Text Document Incremental Updates', () => {
 		assert.equal(document.lineCount, 1);
 		assertValidLineNumbers(document);
 	});
-});
\ No newline at end of file
+});