Add a helper function for rendering a discussion section as HTML (#1388)

* Add a helper function for rendering a discussion section as HTML

rdar://163326857

* Integrate the discussion section in the HTML renderer

Author: d-ronnqvist

Sources/DocCHTML/CMakeLists.txt

@@ -12,6 +12,7 @@ add_library(DocCHTML STATIC
   MarkdownRenderer+Availability.swift
   MarkdownRenderer+Breadcrumbs.swift
   MarkdownRenderer+Declaration.swift
+  MarkdownRenderer+Discussion.swift
   MarkdownRenderer+Parameters.swift
   MarkdownRenderer+Returns.swift
   MarkdownRenderer+Topics.swift

Sources/DocCHTML/MarkdownRenderer+Discussion.swift

@@ -0,0 +1,40 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2025 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+#if canImport(FoundationXML)
+// TODO: Consider other HTML rendering options as a future improvement (rdar://165755530)
+package import FoundationXML
+#else
+package import Foundation
+#endif
+
+package import Markdown
+
+package extension MarkdownRenderer {
+ 
+    /// Creates a discussion section with the given markup.
+    ///
+    /// If the markup doesn't start with a level-2 heading, the renderer will insert a level-2 heading based on the `fallbackSectionName`.
+    func discussion(_ markup: [any Markup], fallbackSectionName: String) -> [XMLNode] {
+        guard !markup.isEmpty else { return [] }
+        var remaining = markup[...]
+        
+        let sectionName: String
+        // Check if the markup already contains an explicit heading
+        if let heading = remaining.first as? Heading, heading.level == 2 {
+            _ = remaining.removeFirst() // Remove the heading so that it's not rendered twice
+            sectionName = heading.plainText
+        } else {
+            sectionName = fallbackSectionName
+        }
+        
+        return selfReferencingSection(named: sectionName, content: remaining.map { visit($0) })
+    }
+}

Sources/SwiftDocC/Model/Rendering/HTML/HTMLRenderer.swift

@@ -178,6 +178,13 @@ struct HTMLRenderer {
             hero.addChild(paragraph)
         }
 
+        // Discussion
+        if let discussion = article.discussion {
+            articleElement.addChildren(
+                renderer.discussion(discussion.content, fallbackSectionName: "Overview")
+            )
+        }
+        
         return RenderedPageInfo(
             content: goal == .richness ? main : articleElement,
             metadata: .init(
@@ -223,6 +230,13 @@ struct HTMLRenderer {
             hero.addChild(paragraph)
         }
 
+        // Discussion
+        if let discussion = symbol.discussion {
+            articleElement.addChildren(
+                renderer.discussion(discussion.content, fallbackSectionName: symbol.kind.identifier.swiftSymbolCouldHaveChildren ? "Overview" : "Discussion")
+            )
+        }
+        
         return RenderedPageInfo(
             content: goal == .richness ? main : articleElement,
             metadata: .init(

Tests/DocCHTMLTests/MarkdownRenderer+PageElementsTests.swift

@@ -641,6 +641,79 @@ struct MarkdownRenderer_PageElementsTests {
         }
     }
 
+    @Test(arguments: RenderGoal.allCases)
+    func testEmptyDiscussionSection(goal: RenderGoal) {
+        let renderer = makeRenderer(goal: goal)
+        let discussion = renderer.discussion([], fallbackSectionName: "Fallback")
+        #expect(discussion.isEmpty)
+    }
+    
+    @Test(arguments: RenderGoal.allCases)
+    func testDiscussionSectionWithoutHeading(goal: RenderGoal) {
+        let renderer = makeRenderer(goal: goal)
+        let discussion = renderer.discussion(parseMarkup(string: """
+        First paragraph
+        
+        Second paragraph
+        """), fallbackSectionName: "Fallback")
+        
+        let commonHTML = """
+        <p>First paragraph</p>
+        <p>Second paragraph</p>
+        """
+        
+        switch goal {
+        case .richness:
+            discussion.assertMatches(prettyFormatted: true, expectedXMLString: """
+            <section id="Fallback">
+            <h2>
+              <a href="#Fallback">Fallback</a>
+            </h2>
+            \(commonHTML)
+            </section>
+            """)
+        case .conciseness:
+            discussion.assertMatches(prettyFormatted: true, expectedXMLString: """
+            <h2>Fallback</h2>
+            \(commonHTML)
+            """)
+        }
+    }
+    
+    @Test(arguments: RenderGoal.allCases)
+    func testDiscussionSectionWithHeading(goal: RenderGoal) {
+        let renderer = makeRenderer(goal: goal)
+        let discussion = renderer.discussion(parseMarkup(string: """
+        ## Some Heading
+        
+        First paragraph
+        
+        Second paragraph
+        """), fallbackSectionName: "Fallback")
+        
+        let commonHTML = """
+        <p>First paragraph</p>
+        <p>Second paragraph</p>
+        """
+        
+        switch goal {
+        case .richness:
+            discussion.assertMatches(prettyFormatted: true, expectedXMLString: """
+            <section id="Some-Heading">
+            <h2>
+              <a href="#Some-Heading">Some Heading</a>
+            </h2>
+            \(commonHTML)
+            </section>
+            """)
+        case .conciseness:
+            discussion.assertMatches(prettyFormatted: true, expectedXMLString: """
+            <h2>Some Heading</h2>
+            \(commonHTML)
+            """)
+        }
+    }
+    
     // MARK: -
 
     private func makeRenderer(

Tests/SwiftDocCUtilitiesTests/FileWritingHTMLContentConsumerTests.swift

@@ -242,6 +242,8 @@ final class FileWritingHTMLContentConsumerTests: XCTestCase {
                   <h1>someMethod(with:and:)</h1>
                   <p>Some in-source description of this method.</p>
                 </section>
+                <h2>Discussion</h2>
+                <p>Further description of this method and how to use it.</p>
               </article>
             </noscript>
             <div id="app"></div>
@@ -264,6 +266,10 @@ final class FileWritingHTMLContentConsumerTests: XCTestCase {
                   <h1>Some article</h1>
                   <p>This is an <i>formatted</i> article.</p>
                 </section>
+                <h2>Custom discussion</h2>
+                <p>It explains how a developer can perform some task using <a href="../someclass/index.html"><code>SomeClass</code></a> in this module.</p>
+                <h3>Details</h3>
+                <p>This subsection describes something more detailed.</p>
               </article>
             </noscript>
             <div id="app"></div>