Expand iOS platform to include iPadOS and Mac Catalyst in declaration fragments

Automatically expands iOS to include its fallback platforms (iPadOS and Mac Catalyst) in declaration fragment platform arrays to ensure consistent platform representation. Uses the existing DefaultAvailability.fallbackPlatforms mapping to determine which platforms should be included when a base platform is present.

rdar://158142013

Author: RalucaP

Sources/SwiftDocC/Model/Rendering/RenderSectionTranslator/DeclarationsSectionTranslator.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2021-2024 Apple Inc. and the Swift project authors
+ Copyright (c) 2021-2025 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
@@ -187,6 +187,26 @@ struct DeclarationsSectionTranslator: RenderSectionTranslator {
                 return declarations
             }
 
+            /// Returns the given platforms with any missing fallback platforms added.
+            ///
+            /// This function uses the centralized `DefaultAvailability.fallbackPlatforms` mapping to ensure
+            /// consistency with platform expansion logic used throughout the codebase.
+            ///
+            /// For example, when iOS is present in the platforms array, this function adds iPadOS and Mac Catalyst
+            /// if they are not already included.
+            ///
+            /// - Parameter platforms: The original platforms array.
+            /// - Returns: The platforms array with fallback platforms added where applicable.
+            func expandPlatformsWithFallbacks(_ platforms: [PlatformName?]) -> [PlatformName?] {
+                guard !platforms.isEmpty else { return platforms }
+
+                // Add fallback platforms if their primary platform is present but the fallback is missing
+                let fallbacks = DefaultAvailability.fallbackPlatforms.compactMap { fallback, primary in
+                    platforms.contains(primary) && !platforms.contains(fallback) ? fallback : nil
+                }
+                return platforms + fallbacks
+            }
+
             func comparePlatformNames(_ lhs: PlatformName?, _ rhs: PlatformName?) -> Bool {
                 guard let lhsValue = lhs, let rhsValue = rhs else {
                     return lhs == nil
@@ -204,6 +224,8 @@ struct DeclarationsSectionTranslator: RenderSectionTranslator {
             ]
             for pair in declaration {
                 let (platforms, declaration) = pair
+                let expandedPlatforms = expandPlatformsWithFallbacks(platforms)
+                let platformNames = sortPlatformNames(expandedPlatforms)
 
                 let renderedTokens: [DeclarationRenderSection.Token]
                 let otherDeclarations: DeclarationRenderSection.OtherDeclarations?
@@ -242,7 +264,7 @@ struct DeclarationsSectionTranslator: RenderSectionTranslator {
                 declarations.append(
                     DeclarationRenderSection(
                         languages: languages,
-                        platforms: sortPlatformNames(platforms),
+                        platforms: platformNames,
                         tokens: renderedTokens,
                         otherDeclarations: otherDeclarations
                     )
@@ -252,7 +274,8 @@ struct DeclarationsSectionTranslator: RenderSectionTranslator {
             if let alternateDeclarations = symbol.alternateDeclarationVariants[trait] {
                 for pair in alternateDeclarations {
                     let (platforms, decls) = pair
-                    let platformNames = sortPlatformNames(platforms)
+                    let expandedPlatforms = expandPlatformsWithFallbacks(platforms)
+                    let platformNames = sortPlatformNames(expandedPlatforms)
                     for alternateDeclaration in decls {
                         let renderedTokens = alternateDeclaration.declarationFragments.map(translateFragment)
 

Tests/SwiftDocCTests/Model/SemaToRenderNodeTests.swift

@@ -927,7 +927,6 @@ class SemaToRenderNodeTests: XCTestCase {
     }
 
     func testCompileSymbol() async throws {
-        throw XCTSkip("TDD: Temporarily disabled while implementing platform expansion")
         let (_, bundle, context) = try await testBundleAndContext(copying: "LegacyBundle_DoNotUseInNewTests") { url in
             // Remove the SideClass sub heading to match the expectations of this test
             let graphURL = url.appendingPathComponent("sidekit.symbols.json")
@@ -1174,7 +1173,6 @@ class SemaToRenderNodeTests: XCTestCase {
     }
 
     func testCompileSymbolWithExternalReferences() async throws {
-        throw XCTSkip("TDD: Temporarily disabled while implementing platform expansion")
         class TestSymbolResolver: GlobalExternalSymbolResolver {
             func symbolReferenceAndEntity(withPreciseIdentifier preciseIdentifier: String) -> (ResolvedTopicReference, LinkResolver.ExternalEntity)? {
                 let reference = ResolvedTopicReference(bundleID: "com.test.external.symbols", path: "/\(preciseIdentifier)", sourceLanguage: .objectiveC)

Tests/SwiftDocCTests/Rendering/DeclarationsRenderSectionTests.swift

@@ -134,7 +134,6 @@ class DeclarationsRenderSectionTests: XCTestCase {
     }
 
     func testAlternateDeclarations() async throws {
-        throw XCTSkip("TDD: Temporarily disabled while implementing platform expansion")
         let (bundle, context) = try await testBundleAndContext(named: "AlternateDeclarations")
         let reference = ResolvedTopicReference(
             bundleID: bundle.id,
@@ -162,7 +161,6 @@ class DeclarationsRenderSectionTests: XCTestCase {
     }
 
     func testPlatformSpecificDeclarations() async throws {
-        throw XCTSkip("TDD: Temporarily disabled while implementing platform expansion")
         // init(_ content: MyClass) throws
         let declaration1: SymbolGraph.Symbol.DeclarationFragments = .init(declarationFragments: [
             .init(kind: .keyword, spelling: "init", preciseIdentifier: nil),

Tests/SwiftDocCTests/Rendering/RenderNodeTranslatorSymbolVariantsTests.swift

@@ -368,7 +368,6 @@ class RenderNodeTranslatorSymbolVariantsTests: XCTestCase {
     }
 
     func testDeclarationsSectionVariants() async throws {
-        throw XCTSkip("TDD: Temporarily disabled while implementing platform expansion")
         func declarationSection(in renderNode: RenderNode) throws -> DeclarationRenderSection {
             try XCTUnwrap(
                 (renderNode.primaryContentSections.first as? DeclarationsRenderSection)?.declarations.first