fix #76076

src/vs/base/common/buffer.ts

@@ -78,7 +78,10 @@ export class VSBuffer {
 	}
 
 	slice(start?: number, end?: number): VSBuffer {
-		return new VSBuffer(this.buffer.slice(start, end));
+		// IMPORTANT: use subarray instead of slice because TypedArray#slice
+		// creates shallow copy and NodeBuffer#slice doesn't. The use of subarray
+		// ensures the same, performant, behaviour.
+		return new VSBuffer(this.buffer.subarray(start!/*bad lib.d.ts*/, end));
 	}
 
 	set(array: VSBuffer, offset?: number): void {

src/vs/base/test/common/buffer.test.ts → src/vs/base/test/node/buffer.test.ts

@@ -364,4 +364,42 @@ suite('Buffer', () => {
 		assert.equal(ended, false);
 		assert.equal(errors.length, 0);
 	});
+
+	test('Performance issue with VSBuffer#slice #76076', function () {
+		// Buffer#slice creates a view
+		{
+			const buff = Buffer.from([10, 20, 30, 40]);
+			const b2 = buff.slice(1, 3);
+			assert.equal(buff[1], 20);
+			assert.equal(b2[0], 20);
+
+			buff[1] = 17; // modify buff AND b2
+			assert.equal(buff[1], 17);
+			assert.equal(b2[0], 17);
+		}
+
+		// TypedArray#slice creates a copy
+		{
+			const unit = new Uint8Array([10, 20, 30, 40]);
+			const u2 = unit.slice(1, 3);
+			assert.equal(unit[1], 20);
+			assert.equal(u2[0], 20);
+
+			unit[1] = 17; // modify unit, NOT b2
+			assert.equal(unit[1], 17);
+			assert.equal(u2[0], 20);
+		}
+
+		// TypedArray#subarray creates a view
+		{
+			const unit = new Uint8Array([10, 20, 30, 40]);
+			const u2 = unit.subarray(1, 3);
+			assert.equal(unit[1], 20);
+			assert.equal(u2[0], 20);
+
+			unit[1] = 17; // modify unit AND b2
+			assert.equal(unit[1], 17);
+			assert.equal(u2[0], 17);
+		}
+	});
 });