Mithril 2 update (#2255)

* Update frontend to Mithril 2

- Update Mithril version to v2.0.4
- Add Typescript typings for Mithril
- Rename "props" to "attrs"; "initProps" to "initAttrs"; "m.prop" to "m.stream"; "m.withAttr" to "utils/withAttr".
- Use Mithril 2's new lifecycle hooks
- SubtreeRetainer has been rewritten to be more useful for the new system
- Utils for forcing page re-initializations have been added (force attr in links, setRouteWithForcedRefresh util)
- Other mechanical changes, following the upgrade guide
- Remove some of the custom stuff in our Component base class
- Introduce "fragments" for non-components that control their own DOM
- Remove Mithril patches, introduce a few new ones (route attrs in <a>; 
- Redesign AlertManagerState `show` with 3 overloads: `show(children)`, `show(attrs, children)`, `show(componentClass, attrs, children)`
- The `affixedSidebar` util has been replaced with an `AffixedSidebar` component

Challenges:
- `children` and `tag` are now reserved, and can not be used as attr names
- Behavior of links to current page changed in Mithril. If moving to a page that is handled by the same component, the page component WILL NOT be re-initialized by default. Additional code to keep track of the current url is needed (See IndexPage, DiscussionPage, and UserPage for examples)
- Native Promise rejections are shown on console when not handled
- Instances of components can no longer be stored. The state pattern should be used instead.

Refs #1821.

Co-authored-by: Alexander Skvortsov <sasha.skvortsov109@gmail.com>
Co-authored-by: Matthew Kilgore <tankerkiller125@gmail.com>
Co-authored-by: Franz Liedke <franz@develophp.org>

js/src/admin/components/AppearancePage.js

@@ -6,15 +6,16 @@ import EditCustomHeaderModal from './EditCustomHeaderModal';
 import EditCustomFooterModal from './EditCustomFooterModal';
 import UploadImageButton from './UploadImageButton';
 import saveSettings from '../utils/saveSettings';
+import withAttr from '../../common/utils/withAttr';
 
 export default class AppearancePage extends Page {
-  init() {
-    super.init();
+  oninit(vnode) {
+    super.oninit(vnode);
 
-    this.primaryColor = m.prop(app.data.settings.theme_primary_color);
-    this.secondaryColor = m.prop(app.data.settings.theme_secondary_color);
-    this.darkMode = m.prop(app.data.settings.theme_dark_mode);
-    this.coloredHeader = m.prop(app.data.settings.theme_colored_header);
+    this.primaryColor = m.stream(app.data.settings.theme_primary_color);
+    this.secondaryColor = m.stream(app.data.settings.theme_secondary_color);
+    this.darkMode = m.stream(app.data.settings.theme_dark_mode);
+    this.coloredHeader = m.stream(app.data.settings.theme_colored_header);
   }
 
   view() {
@@ -27,40 +28,34 @@ export default class AppearancePage extends Page {
               <div className="helpText">{app.translator.trans('core.admin.appearance.colors_text')}</div>
 
               <div className="AppearancePage-colors-input">
-                <input
-                  className="FormControl"
-                  type="text"
-                  placeholder="#aaaaaa"
-                  value={this.primaryColor()}
-                  onchange={m.withAttr('value', this.primaryColor)}
-                />
-                <input
-                  className="FormControl"
-                  type="text"
-                  placeholder="#aaaaaa"
-                  value={this.secondaryColor()}
-                  onchange={m.withAttr('value', this.secondaryColor)}
-                />
+                <input className="FormControl" type="text" placeholder="#aaaaaa" bidi={this.primaryColor} />
+                <input className="FormControl" type="text" placeholder="#aaaaaa" bidi={this.secondaryColor} />
               </div>
 
-              {Switch.component({
-                state: this.darkMode(),
-                children: app.translator.trans('core.admin.appearance.dark_mode_label'),
-                onchange: this.darkMode,
-              })}
+              {Switch.component(
+                {
+                  state: this.darkMode(),
+                  onchange: this.darkMode,
+                },
+                app.translator.trans('core.admin.appearance.dark_mode_label')
+              )}
 
-              {Switch.component({
-                state: this.coloredHeader(),
-                children: app.translator.trans('core.admin.appearance.colored_header_label'),
-                onchange: this.coloredHeader,
-              })}
+              {Switch.component(
+                {
+                  state: this.coloredHeader(),
+                  onchange: this.coloredHeader,
+                },
+                app.translator.trans('core.admin.appearance.colored_header_label')
+              )}
 
-              {Button.component({
-                className: 'Button Button--primary',
-                type: 'submit',
-                children: app.translator.trans('core.admin.appearance.submit_button'),
-                loading: this.loading,
-              })}
+              {Button.component(
+                {
+                  className: 'Button Button--primary',
+                  type: 'submit',
+                  loading: this.loading,
+                },
+                app.translator.trans('core.admin.appearance.submit_button')
+              )}
             </fieldset>
           </form>
 
@@ -79,31 +74,37 @@ export default class AppearancePage extends Page {
           <fieldset>
             <legend>{app.translator.trans('core.admin.appearance.custom_header_heading')}</legend>
             <div className="helpText">{app.translator.trans('core.admin.appearance.custom_header_text')}</div>
-            {Button.component({
-              className: 'Button',
-              children: app.translator.trans('core.admin.appearance.edit_header_button'),
-              onclick: () => app.modal.show(EditCustomHeaderModal),
-            })}
+            {Button.component(
+              {
+                className: 'Button',
+                onclick: () => app.modal.show(EditCustomHeaderModal),
+              },
+              app.translator.trans('core.admin.appearance.edit_header_button')
+            )}
           </fieldset>
 
           <fieldset>
             <legend>{app.translator.trans('core.admin.appearance.custom_footer_heading')}</legend>
             <div className="helpText">{app.translator.trans('core.admin.appearance.custom_footer_text')}</div>
-            {Button.component({
-              className: 'Button',
-              children: app.translator.trans('core.admin.appearance.edit_footer_button'),
-              onclick: () => app.modal.show(EditCustomFooterModal),
-            })}
+            {Button.component(
+              {
+                className: 'Button',
+                onclick: () => app.modal.show(EditCustomFooterModal),
+              },
+              app.translator.trans('core.admin.appearance.edit_footer_button')
+            )}
           </fieldset>
 
           <fieldset>
             <legend>{app.translator.trans('core.admin.appearance.custom_styles_heading')}</legend>
             <div className="helpText">{app.translator.trans('core.admin.appearance.custom_styles_text')}</div>
-            {Button.component({
-              className: 'Button',
-              children: app.translator.trans('core.admin.appearance.edit_css_button'),
-              onclick: () => app.modal.show(EditCustomCssModal),
-            })}
+            {Button.component(
+              {
+                className: 'Button',
+                onclick: () => app.modal.show(EditCustomCssModal),
+              },
+              app.translator.trans('core.admin.appearance.edit_css_button')
+            )}
           </fieldset>
         </div>
       </div>