Distribute paste to multiple cursors only if it originated with the same...

Distribute paste to multiple cursors only if it originated with the same number of multiple cursors (fixes #16155)

src/vs/editor/common/controller/cursorTypeOperations.ts

@@ -122,18 +122,7 @@ export class TypeOperations {
 			return multicursorText;
 		}
 
-		for (let i = 0; i < selections.length; i++) {
-			if (selections[i].startLineNumber !== selections[i].endLineNumber) {
-				return null;
-			}
-		}
-
-		let pastePieces = text.split(/\r\n|\r|\n/);
-		if (pastePieces.length !== selections.length) {
-			return null;
-		}
-
-		return pastePieces;
+		return null;
 	}
 
 	public static paste(config: CursorConfiguration, model: ICursorSimpleModel, selections: Selection[], text: string, pasteOnNewLine: boolean, multicursorText: string[]): EditOperationResult {

src/vs/editor/contrib/multicursor/test/multicursor.test.ts

@@ -27,7 +27,13 @@ suite('Multicursor', () => {
 			addCursorUpAction.run(null, editor, {});
 			assert.equal(cursor.getSelections().length, 2);
 
-			editor.trigger('test', Handler.Paste, { text: '1\n2' });
+			editor.trigger('test', Handler.Paste, {
+				text: '1\n2',
+				multicursorText: [
+					'1',
+					'2'
+				]
+			});
 			// cursorCommand(cursor, H.Paste, { text: '1\n2' });
 			assert.equal(editor.getModel().getLineContent(1), '1abc');
 			assert.equal(editor.getModel().getLineContent(2), '2def');

src/vs/editor/test/browser/controller/cursor.test.ts

@@ -1447,6 +1447,49 @@ suite('Editor Controller - Regression tests', () => {
 		});
 	});
 
+	test('issue #16155: Paste into multiple cursors has edge case when number of lines equals number of cursors - 1', () => {
+		usingCursor({
+			text: [
+				'test',
+				'test',
+				'test',
+				'test'
+			],
+		}, (model, cursor) => {
+			cursor.setSelections('test', [
+				new Selection(1, 1, 1, 5),
+				new Selection(2, 1, 2, 5),
+				new Selection(3, 1, 3, 5),
+				new Selection(4, 1, 4, 5),
+			]);
+
+			cursorCommand(cursor, H.Paste, {
+				text: 'aaa\nbbb\nccc\n',
+				pasteOnNewLine: false,
+				multicursorText: null
+			});
+
+			assert.equal(model.getValue(), [
+				'aaa',
+				'bbb',
+				'ccc',
+				'',
+				'aaa',
+				'bbb',
+				'ccc',
+				'',
+				'aaa',
+				'bbb',
+				'ccc',
+				'',
+				'aaa',
+				'bbb',
+				'ccc',
+				'',
+			].join('\n'));
+		});
+	});
+
 	test('issue #3071: Investigate why undo stack gets corrupted', () => {
 		let model = Model.createFromString(
 			[