Surface category one liner on index page (#3632)

* Surface category one liner on index page

* Regenerate renderers

Author: parlough

lib/src/generator/templates.aot_renderers_for_html.dart

@@ -1048,6 +1048,13 @@ String renderIndex(PackageTemplateData context0) {
           <h3>''');
       buffer.writeEscaped(context8.name);
       buffer.write('''</h3>''');
+      if (context8.isDocumented) {
+        buffer.writeln();
+        buffer.write('''
+          <p>''');
+        buffer.write(context8.oneLineDoc);
+        buffer.write('''</p>''');
+      }
       var context9 = context8.externalItems;
       for (var context10 in context9) {
         buffer.writeln();

lib/templates/html/index.html

@@ -19,6 +19,9 @@ <h2>{{name}}</h2>
         {{/defaultCategory.publicLibrariesSorted}}
         {{#categoriesWithPublicLibraries}}
           <h3>{{name}}</h3>
+          {{#isDocumented}}
+          <p>{{{ oneLineDoc }}}</p>
+          {{/isDocumented}}
           {{#externalItems}}
             <dt>
               <span class="name">

test/templates/category_test.dart

@@ -21,6 +21,7 @@ void main() async {
   late PackageMetaProvider packageMetaProvider;
   late DartdocGeneratorOptionContext context;
   late List<String> topicOneLines;
+  late List<String> indexPageLines;
 
   Future<PubPackageBuilder> createPackageBuilder() async {
     context = await utils.generatorContextFromArgv([
@@ -75,6 +76,8 @@ dartdoc:
   categories:
     One:
       markdown: one.md
+    Documented:
+      markdown: documented.md  
 ''',
       libFiles: [
         d.file('lib.dart', '''
@@ -118,10 +121,15 @@ extension Ex on int {}
 /// An extension type.
 /// {@category One}
 extension type ExType(int it) {}
+'''),
+        d.file('other.dart', '''
+/// {@category Documented}
+library;      
 '''),
       ],
       files: [
         d.file('one.md', ''),
+        d.file('documented.md', 'First line.\n\nSecond line.'),
       ],
       resourceProvider: resourceProvider,
     );
@@ -131,6 +139,10 @@ extension type ExType(int it) {}
         .getFile(path.join(packagePath, 'doc', 'topics', 'One-topic.html'))
         .readAsStringSync()
         .split('\n');
+    indexPageLines = resourceProvider
+        .getFile(path.join(packagePath, 'doc', 'index.html'))
+        .readAsStringSync()
+        .split('\n');
   });
 
   test('page links to classes annotated with category', () async {
@@ -296,4 +308,11 @@ extension type ExType(int it) {}
       ]),
     );
   });
+
+  test('index page includes topics and their one liner description', () {
+    indexPageLines.expectMainContentContainsAllInOrder([
+      equalsIgnoringWhitespace('<h3>Documented</h3>'),
+      equalsIgnoringWhitespace('<p>First line.</p>'),
+    ]);
+  });
 }