Fix availability logic refactor (#1065)

Refactor symbol availability logic.

This refactor was initiated by the need of stop using the module operating system name as an availability item.

This change required a big refactoring of the logic, and now the symbol graph availability loading logic is like the following:
1. Every symbol graph is loaded and the symbols get only the availability information that's marked in the SDK.
2. Once all the SGFs are oaded, whe iterate over the symbols and we add the fallbkac and default availability if applies.

* Refactor unit tests for testing symbol availability.

* Refactor fallback platforms data structure.

Instead of making a `[(FallbackPlatform, InheritedPlaform)].
The new struture to hold this information is in the way of `[InheritedPlatfor:[FallbackPlatforms]]`.

Author: sofiaromorales

Sources/SwiftDocC/Infrastructure/Symbol Graph/SymbolGraphLoader.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
@@ -131,28 +131,30 @@ public struct DefaultAvailability: Codable, Equatable {
 
     /// Fallback availability information for platforms we either don't emit SGFs for
     /// or have the same availability information as another platform.
-    package static let fallbackPlatforms: [PlatformName: PlatformName] = [
-        .catalyst: .iOS,
-        .iPadOS: .iOS,
-    ]
+    ///
+    /// The key corresponds to the fallback platform and the value to the platform it's
+    /// fallbacking from.
+    package static let fallbackPlatforms: [PlatformName: [PlatformName]] = [.iOS: [.catalyst, .iPadOS]]
 
     /// Creates a default availability module.
     /// - Parameter modules: A map of modules and the default platform availability for symbols in that module.
     public init(with modules: [String: [ModuleAvailability]]) {
             self.modules = modules.mapValues { platformAvailabilities -> [DefaultAvailability.ModuleAvailability] in
             // If a module doesn't contain default availability information for any of the fallback platforms,
             // infer it from the corresponding mapped value.
-            platformAvailabilities + DefaultAvailability.fallbackPlatforms.compactMap { (platform, fallbackPlatform) in
-                if !platformAvailabilities.contains(where: { $0.platformName == platform }),
-                   let fallbackAvailability = platformAvailabilities.first(where: { $0.platformName == fallbackPlatform }),
-                   let fallbackIntroducedVersion = fallbackAvailability.introducedVersion
-                {
-                    return DefaultAvailability.ModuleAvailability(
-                        platformName: platform,
-                        platformVersion: fallbackIntroducedVersion
-                    )
+            platformAvailabilities + DefaultAvailability.fallbackPlatforms.flatMap { (fallbackPlatform, platform) in
+                platform.compactMap { platformName in
+                    if !platformAvailabilities.contains(where: { $0.platformName == platformName }),
+                       let fallbackAvailability = platformAvailabilities.first(where: { $0.platformName == fallbackPlatform }),
+                       let fallbackIntroducedVersion = fallbackAvailability.introducedVersion
+                    {
+                        return DefaultAvailability.ModuleAvailability(
+                            platformName: platformName,
+                            platformVersion: fallbackIntroducedVersion
+                        )
+                    }
+                    return nil
                 }
-                return nil
             }
         }
     }

Sources/SwiftDocC/Infrastructure/Workspace/DefaultAvailability.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
@@ -591,10 +591,12 @@ extension Symbol {
     func mergeAvailabilities(unifiedSymbol: UnifiedSymbolGraph.Symbol) {
         for (selector, mixins) in unifiedSymbol.mixins {
             let trait = DocumentationDataVariantsTrait(for: selector)
-            if let unifiedSymbolAvailability = mixins[SymbolGraph.Symbol.Availability.mixinKey] as? SymbolGraph.Symbol.Availability {
+            guard let availabilityVariantTrait = availabilityVariants[trait] else {
+                return
+            }
+            if let unifiedSymbolAvailability = mixins.getValueIfPresent(for: SymbolGraph.Symbol.Availability.self) {
                 unifiedSymbolAvailability.availability.forEach { availabilityItem in
-                    guard let availabilityVariantTrait = availabilityVariants[trait] else { return }
-                    if (availabilityVariantTrait.availability.contains(where: { $0.domain?.rawValue == availabilityItem.domain?.rawValue })) {
+                    guard availabilityVariantTrait.availability.firstIndex(where: { $0.domain?.rawValue == availabilityItem.domain?.rawValue }) == nil else {
                         return
                     }
                     availabilityVariants[trait]?.availability.append(availabilityItem)

Sources/SwiftDocC/Semantics/Symbol/Symbol.swift

@@ -112,7 +112,7 @@ public struct InfoPlist: File, DataRepresentable {
             self.identifier = identifier
             self.defaultAvailability = defaultAvailability
         }
-
+        
         public init(from decoder: any Decoder) throws {
             let container = try decoder.container(keyedBy: DocumentationBundle.Info.CodingKeys.self)
             displayName = try container.decodeIfPresent(String.self, forKey: .displayName)

Sources/SwiftDocCTestUtilities/FilesAndFolders.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
@@ -145,8 +145,10 @@ public struct ConvertAction: AsyncAction {
         // Inject current platform versions if provided
         if var currentPlatforms {
             // Add missing platforms if their fallback platform is present.
-            for (platform, fallbackPlatform) in DefaultAvailability.fallbackPlatforms where currentPlatforms[platform.displayName] == nil {
-                currentPlatforms[platform.displayName] = currentPlatforms[fallbackPlatform.displayName]
+            for (fallbackPlatform, platforms) in DefaultAvailability.fallbackPlatforms {
+                for platform in platforms where currentPlatforms[platform.displayName] == nil {
+                    currentPlatforms[platform.displayName] = currentPlatforms[fallbackPlatform.displayName]
+                }
             }
             configuration.externalMetadata.currentPlatforms = currentPlatforms
         }