Optimize strings.lcut - fix #34665

src/vs/base/common/strings.ts

@@ -674,7 +674,7 @@ export function computeLineStarts(text: string): number[] {
  * Given a string and a max length returns a shorted version. Shorting
  * happens at favorable positions - such as whitespace or punctuation characters.
  */
-export function lcut(text: string, n: number): string {
+export function lcut_orig(text: string, n: number): string {
 
 	if (text.length < n) {
 		return text;
@@ -695,6 +695,25 @@ export function lcut(text: string, n: number): string {
 	return segments.join(empty).replace(/^\s/, empty);
 }
 
+export function lcut(text: string, n: number) {
+	if (text.length < n) {
+		return text;
+	}
+
+	const re = /\b/g;
+	let i = 0;
+	while (re.test(text)) {
+		if (text.length - re.lastIndex < n) {
+			break;
+		}
+
+		i = re.lastIndex;
+		re.lastIndex += 1;
+	}
+
+	return text.substring(i).replace(/^\s/, empty);
+}
+
 // Escape codes
 // http://en.wikipedia.org/wiki/ANSI_escape_code
 const EL = /\x1B\x5B[12]?K/g; // Erase in line

src/vs/base/test/common/strings.test.ts

@@ -126,6 +126,17 @@ suite('Strings', () => {
 		assertLineStart('far\nboo\nfar', 0, 4, 8);
 	});
 
+	test('lcut', () => {
+		assert.strictEqual(strings.lcut('foo bar', 0), '');
+		assert.strictEqual(strings.lcut('foo bar', 1), 'bar');
+		assert.strictEqual(strings.lcut('foo bar', 3), 'bar');
+		assert.strictEqual(strings.lcut('foo bar', 4), 'bar'); // Leading whitespace trimmed
+		assert.strictEqual(strings.lcut('foo bar', 5), 'foo bar');
+		assert.strictEqual(strings.lcut('test string 0.1.2.3', 3), '2.3');
+
+		assert.strictEqual(strings.lcut('', 10), '');
+		assert.strictEqual(strings.lcut('a', 10), 'a');
+	});
 
 	test('pad', function () {
 		assert.strictEqual(strings.pad(1, 0), '1');