Switch to a more flexible banner format (#12676)

Switch from defining the banner in `src/data/banner.yml` to the
`bannerHtml` field in the `src/data/site.yml` banner alongside
`showBanner`.

I'm not sure this is the solution I want to use long term, but it works
for now.

Author: parlough

site/lib/src/components/layout/banner.dart

@@ -4,57 +4,23 @@
 
 import 'package:jaspr/jaspr.dart';
 
-/// The information to display in the site banner,
-/// as configured in the `src/data/banner.yml` file.
-@immutable
-final class BannerContent {
-  final String text;
-  final String linkText;
-  final String linkUri;
-  final bool newTab;
-
-  const BannerContent({
-    required this.text,
-    required this.linkText,
-    required this.linkUri,
-    this.newTab = false,
-  });
-
-  factory BannerContent.fromMap(Map<String, Object?> bannerData) {
-    final text = bannerData['text'] as String;
-    final link = bannerData['link'] as Map<Object?, Object?>;
-    final linkText = link['text'] as String;
-    final linkUri = link['url'] as String;
-    final newTab = link['newTab'] as bool? ?? false;
-
-    return BannerContent(
-      text: text,
-      linkText: linkText,
-      linkUri: linkUri,
-      newTab: newTab,
-    );
-  }
-}
-
 /// The site-wide banner.
 class DashBanner extends StatelessComponent {
-  const DashBanner(this.content, {super.key});
+  const DashBanner(this.inlineHtmlContent, {super.key});
 
-  final BannerContent content;
+  /// The raw, inline HTML content to render in the banner.
+  ///
+  /// This should only be sourced from managed content,
+  /// such as our checked-in data files.
+  final String inlineHtmlContent;
 
   @override
   Component build(BuildContext context) => div(
     id: 'site-banner',
     attributes: {'role': 'alert'},
     [
       p([
-        text(content.text),
-        text(' '),
-        a(
-          href: content.linkUri,
-          target: content.newTab ? Target.blank : null,
-          [text(content.linkText)],
-        ),
+        raw(inlineHtmlContent),
       ]),
     ],
   );

site/lib/src/layouts/doc_layout.dart

@@ -47,8 +47,9 @@ class DocLayout extends FlutterDocsLayout {
               currentTitle: pageTitle,
             ),
           if (showBanner)
-            if (page.data['banner'] case final Map<String, Object?> bannerData)
-              DashBanner(BannerContent.fromMap(bannerData)),
+            if (siteData['bannerHtml'] case final String bannerHtml
+                when bannerHtml.trim().isNotEmpty)
+              DashBanner(bannerHtml),
           div(classes: 'after-leading-content', [
             if (tocData != null)
               aside(id: 'side-menu', [

src/data/banner.yml

@@ -5,6 +5,13 @@ email: [email protected]
 
 showBanner: true
 
+# The raw, inline HTML to display in the banner.
+# Is automatically wrapped in a paragraph tag.
+bannerHtml: >-
+  Don't miss the live Flutter and Dart Q&A happening
+  today, November 12 at 11am PST.
+  <a href="https://www.youtube.com/watch?v=RTb3gP4p5bw" target="_blank" rel="noopener">Join us!</a>
+
 branch: main
 repo:
   organization: https://github.com/flutter