MM-12944: force "Delete" focus on showing delete post modal (#2020)

Focus handling is a mess. This doesn't really make it much better, other than making the behaviour explicit and constrained to within the modal dialog in question, fixing a regression introduced by MM-12688.

components/delete_post_modal/delete_post_modal.jsx

@@ -17,30 +17,15 @@ export default class DeletePostModal extends React.PureComponent {
  teamName: PropTypes.string,
  post: PropTypes.object.isRequired,
  commentCount: PropTypes.number.isRequired,
-
- /**
- * Does the post come from RHS mode
- */
  isRHS: PropTypes.bool.isRequired,
-
- /**
- * Function called when modal is dismissed
- */
  onHide: PropTypes.func.isRequired,
-
  actions: PropTypes.shape({
-
- /**
- * Function called for deleting post
- */
  deleteAndRemovePost: PropTypes.func.isRequired,
  }),
  }
 
  constructor(props) {
  super(props);
- this.handleDelete = this.handleDelete.bind(this);
- this.onHide = this.onHide.bind(this);
  this.state = {
  show: true,
  };
@@ -66,7 +51,13 @@ export default class DeletePostModal extends React.PureComponent {
  }
  }
 
- onHide() {
+ handleEntered = () => {
+ if (this.deletePostBtn) {
+ this.deletePostBtn.focus();
+ }
+ }
+
+ onHide = () => {
  this.setState({show: false});
 
  if (!UserAgent.isMobile()) {
@@ -111,6 +102,7 @@ export default class DeletePostModal extends React.PureComponent {
  return (
  <Modal
  show={this.state.show}
+ onEntered={this.handleEntered}
  onHide={this.onHide}
  onExited={this.props.onHide}
  enforceFocus={false}

tests/components/__snapshots__/delete_post_modal.test.jsx.snap

@@ -21,6 +21,7 @@ exports[`components/delete_post_modal should match snapshot for delete_post_moda
  "remove": [Function],
  }
  }
+ onEntered={[Function]}
  onExited={[MockFunction]}
  onHide={[Function]}
  renderBackdrop={[Function]}
@@ -123,6 +124,7 @@ exports[`components/delete_post_modal should match snapshot for delete_post_moda
  "remove": [Function],
  }
  }
+ onEntered={[Function]}
  onExited={[MockFunction]}
  onHide={[Function]}
  renderBackdrop={[Function]}

tests/components/delete_post_modal.test.jsx

@@ -43,6 +43,18 @@ describe('components/delete_post_modal', () => {
  expect(wrapper).toMatchSnapshot();
  });
 
+ test('should focus delete button on enter', () => {
+ const wrapper = shallow(
+ <DeletePostModal {...baseProps}/>
+ );
+
+ const deletePostBtn = {focus: jest.fn()};
+ wrapper.instance().deletePostBtn = deletePostBtn;
+
+ wrapper.instance().handleEntered();
+ expect(deletePostBtn.focus).toHaveBeenCalled();
+ });
+
  test('should match state when onHide is called', () => {
  const wrapper = shallow(
  <DeletePostModal {...baseProps}/>