Add :u[ndo] ex command (#4980)

Fixes #3197

src/actions/commands/actions.ts

@@ -2173,7 +2173,7 @@ class CommandGoToOtherEndOfHighlightedText extends BaseCommand {
 }
 
 @RegisterAction
-class CommandUndo extends BaseCommand {
+export class CommandUndo extends BaseCommand {
   modes = [Mode.Normal];
   keys = ['u'];
   runsOnceForEveryCursor() {

src/cmd_line/commands/undo.ts

@@ -0,0 +1,28 @@
+import * as node from '../node';
+import { Logger } from '../../util/logger';
+import { VimState } from '../../state/vimState';
+import { CommandUndo } from '../../actions/commands/actions';
+import { Position } from '../../common/motion/position';
+
+//
+//  Implements :u[ndo]
+//  http://vimdoc.sourceforge.net/htmldoc/undo.html
+//
+export class UndoCommand extends node.CommandBase {
+  protected _arguments: {};
+  private readonly _logger = Logger.get('Undo');
+
+  constructor(args: {}) {
+    super();
+    this._arguments = args;
+  }
+
+  get arguments(): {} {
+    return this._arguments;
+  }
+
+  async execute(vimState: VimState): Promise<void> {
+    await new CommandUndo().exec(new Position(0, 0), vimState);
+    return;
+  }
+}

src/cmd_line/subparser.ts

@@ -21,6 +21,7 @@ import { parseHistoryCommandArgs } from './subparsers/history';
 import { NohlCommand } from './commands/nohl';
 import { OnlyCommand } from './commands/only';
 import { SmileCommand } from './commands/smile';
+import { UndoCommand } from './commands/undo';
 
 // Associates a name and an abbreviation with a command parser
 export type CommandParserMapping = {
@@ -194,6 +195,11 @@ export const commandParsers = {
     parser: tabCmd.parseTabPCommandArgs,
   },
 
+  undo: {
+    abbrev: 'u',
+    parser: () => new UndoCommand({}),
+  },
+
   vnew: {
     abbrev: 'vne',
     parser: fileCmd.parseEditNewFileInNewVerticalWindowCommandArgs,

test/cmd_line/undo.test.ts

@@ -0,0 +1,23 @@
+import { getAndUpdateModeHandler } from '../../extension';
+import { commandLine } from '../../src/cmd_line/commandLine';
+import { ModeHandler } from '../../src/mode/modeHandler';
+import { assertEqualLines, cleanUpWorkspace, setupWorkspace } from '../testUtils';
+import { VimState } from '../../src/state/vimState';
+
+suite('Undo command', () => {
+  let modeHandler: ModeHandler;
+
+  setup(async () => {
+    await setupWorkspace();
+    modeHandler = await getAndUpdateModeHandler();
+  });
+
+  teardown(cleanUpWorkspace);
+
+  test('undoes last action after insert mode', async () => {
+    await modeHandler.handleMultipleKeyEvents(['i', 'a', '<Esc>']);
+    await modeHandler.handleMultipleKeyEvents(['i', 'b', '<Esc>']);
+    await commandLine.Run('undo', modeHandler.vimState);
+    assertEqualLines(['a']);
+  });
+});