Don't emit variants for article-only catalogs

For article-only catalogs, i.e., catalogs that use @TechnologyRoot,
don't emit the variants array in the render node, so that renderers
don't display the page's language, since it doesn't have a language.

A longer-term fix here would be to not consider articles in article-only
catalogs to be "Swift", and implement logic in RenderNodeTranslator to
not emit variants information for language-less pages
(github.com/swiftlang/issues/240).

rdar://92758192

Author: franklinsch

Sources/SwiftDocC/Infrastructure/DocumentationContext.swift

@@ -1877,7 +1877,10 @@ public class DocumentationContext: DocumentationContextDataProviderDelegate {
         let reference = ResolvedTopicReference(
             bundleIdentifier: bundle.identifier,
             path: path,
-            sourceLanguages: availableSourceLanguages ?? [.swift]
+            sourceLanguages: availableSourceLanguages
+                // FIXME: Pages in article-only catalogs should not be inferred as "Swift" as a fallback
+                // (github.com/apple/swift-docc/issues/240).
+                ?? [.swift]
         )
 
         let title = article.topicGraphNode.title

Sources/SwiftDocC/Model/Rendering/RenderNodeTranslator.swift

@@ -601,7 +601,14 @@ public struct RenderNodeTranslator: SemanticVisitor {
         collectedTopicReferences.append(contentsOf: hierarchyTranslator.collectedTopicReferences)
         node.hierarchy = hierarchy
 
-        node.variants = variants(for: documentationNode)
+        // Emit variants only if we're not compiling an article-only catalog to prevent renderers from
+        // advertising the page as "Swift", which is the language DocC assigns to pages in article only pages.
+        // (github.com/apple/swift-docc/issues/240).
+        if let topLevelModule = context.soleRootModuleReference,
+           try! context.entity(with: topLevelModule).kind.isSymbol
+        {
+            node.variants = variants(for: documentationNode)
+        }
 
         if let abstract = article.abstractSection,
             let abstractContent = visitMarkup(abstract.content) as? [RenderInlineContent] {

Tests/SwiftDocCTests/Model/SemaToRenderNodeArticleOnlyCatalogTests.swift

@@ -0,0 +1,20 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2022 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
+*/
+
+import XCTest
+@testable import SwiftDocC
+
+class SemaToRenderNodeArticleOnlyCatalogTests: XCTestCase {
+    func testDoesNotEmitVariantsForPagesInArticleOnlyCatalog() throws {
+        for renderNode in try renderNodeConsumer(for: "BundleWithTechnologyRoot").allRenderNodes() {
+            XCTAssertNil(renderNode.variants)
+        }
+    }
+}