Lazy load components (#3879)

* feat: Lazy-load routes

* feat: Lazy-load modals

* feat: Lazy-load columns

* refactor: Simplify Bundle API

* feat: Optimize bundles

* feat: Prevent flashing the waiting state

* feat: Preload commonly used bundles

* feat: Lazy load Compose reducers

* feat: Lazy load Notifications reducer

* refactor: Move all dynamic imports into one file

* fix: Minor bugs

* fix: Manually hydrate the lazy-loaded reducers

* refactor: Move all dynamic imports to async-components

* fix: Loading modal style

* refactor: Avoid converting the raw state for each lazy hydration

* refactor: Remove unused component

* refactor: Maintain modal name

* fix: Add as=script to preload link

* chore: Fix lint error

* fix(components/bundle): Check if timestamp is set when computing elapsed

* fix: Load compose reducers for the onboarding modal

app/javascript/mastodon/features/ui/util/react_router_helpers.js

@@ -0,0 +1,65 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import Switch from 'react-router-dom/Switch';
+import Route from 'react-router-dom/Route';
+
+import ColumnLoading from '../components/column_loading';
+import BundleColumnError from '../components/bundle_column_error';
+import BundleContainer from '../containers/bundle_container';
+
+// Small wrapper to pass multiColumn to the route components
+export const WrappedSwitch = ({ multiColumn, children }) => (
+  <Switch>
+    {React.Children.map(children, child => React.cloneElement(child, { multiColumn }))}
+  </Switch>
+);
+
+WrappedSwitch.propTypes = {
+  multiColumn: PropTypes.bool,
+  children: PropTypes.node,
+};
+
+// Small Wraper to extract the params from the route and pass
+// them to the rendered component, together with the content to
+// be rendered inside (the children)
+export class WrappedRoute extends React.Component {
+
+  static propTypes = {
+    component: PropTypes.func.isRequired,
+    content: PropTypes.node,
+    multiColumn: PropTypes.bool,
+  }
+
+  renderComponent = ({ match }) => {
+    this.match = match; // Needed for this.renderBundle
+
+    const { component } = this.props;
+
+    return (
+      <BundleContainer fetchComponent={component} loading={this.renderLoading} error={this.renderError}>
+        {this.renderBundle}
+      </BundleContainer>
+    );
+  }
+
+  renderLoading = () => {
+    return <ColumnLoading />;
+  }
+
+  renderError = (props) => {
+    return <BundleColumnError {...props} />;
+  }
+
+  renderBundle = (Component) => {
+    const { match: { params }, props: { content, multiColumn } } = this;
+
+    return <Component params={params} multiColumn={multiColumn}>{content}</Component>;
+  }
+
+  render () {
+    const { component: Component, content, ...rest } = this.props;
+
+    return <Route {...rest} render={this.renderComponent} />;
+  }
+
+}