Support authoring a single anonymous topics section

Sources/SwiftDocC/Infrastructure/DocumentationContext.swift

@@ -400,7 +400,6 @@ public class DocumentationContext: DocumentationContextDataProviderDelegate {
             MissingAbstract(sourceFile: source).any(),
             NonOverviewHeadingChecker(sourceFile: source).any(),
             SeeAlsoInTopicsHeadingChecker(sourceFile: source).any(),
-            TopicsSectionWithoutSubheading(sourceFile: source).any(),
         ])
         checker.visit(document)
         diagnosticEngine.emit(checker.problems)

Sources/SwiftDocC/Model/DocumentationMarkup.swift

@@ -247,6 +247,14 @@ struct DocumentationMarkup {
                         topicsFirstTaskGroupIndex = index
                     }
                 }
+                // The first topic group in a topic section is allowed to be "anonymous", or without
+                // an H3 heading. We account for this by treating both UnorderedLists and Paragraphs as
+                // valid children indicating the start of a task group.
+                else if child is UnorderedList {
+                    topicsFirstTaskGroupIndex = index
+                } else if child is Paragraph {
+                    topicsFirstTaskGroupIndex = index
+                }
 
                 if topicsIndex == nil { topicsIndex = index }
 

Tests/SwiftDocCTests/Model/SemaToRenderNodeTests.swift

@@ -3174,4 +3174,45 @@ Document
             ]
         )
     }
+
+    func testTopicsSectionWithSingleAnonymousTopicGroup() throws {
+        let (_, bundle, context) = try testBundleAndContext(
+            copying: "TestBundle",
+            configureBundle: { url in
+                try """
+                # Article
+
+                Abstract.
+
+                ## Topics
+
+                - ``MyKit/MyProtocol``
+                - ``MyKit/MyClass``
+
+                """.write(to: url.appendingPathComponent("article.md"), atomically: true, encoding: .utf8)
+            }
+        )
+
+        let articleReference = ResolvedTopicReference(
+            bundleIdentifier: bundle.identifier,
+            path: "/documentation/Test-Bundle/article",
+            sourceLanguage: .swift
+        )
+
+        let articleNode = try context.entity(with: articleReference)
+
+        var translator = RenderNodeTranslator(context: context, bundle: bundle, identifier: articleNode.reference, source: nil)
+        let articleRenderNode = try XCTUnwrap(translator.visit(articleNode.semantic) as? RenderNode)
+
+        XCTAssertEqual(
+            articleRenderNode.topicSections.flatMap { taskGroup in
+                [taskGroup.title] + taskGroup.identifiers
+            },
+            [
+                nil,
+                "doc://org.swift.docc.example/documentation/MyKit/MyProtocol",
+                "doc://org.swift.docc.example/documentation/MyKit/MyClass",
+            ]
+        )
+    }
 }