Use availability item platform name to compute default availability information. (#1208)

Use availability item platform name to compute default availability information.

This change makes a small tweak to the default availability logic so it uses the
symbol availability item platform name instead of the symbol graph platform name
to calculate the corresponding default introduced version from the default
availability.

rdar://146774862

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
@@ -317,9 +317,10 @@ struct SymbolGraphLoader {
 
                 // Fill introduced versions when missing.
                 availability.availability = availability.availability.map {
-                    $0.fillingMissingIntroducedVersion(
+                    let availabilityPlatformName = $0.domain.map { PlatformName(operatingSystemName: $0.rawValue) } ?? platformName
+                    return $0.fillingMissingIntroducedVersion(
                         from: defaultAvailabilityVersionByPlatform,
-                        fallbackPlatform: DefaultAvailability.fallbackPlatforms[platformName]?.rawValue
+                        fallbackPlatform: DefaultAvailability.fallbackPlatforms[availabilityPlatformName]?.rawValue
                     )
                 }
                 // Add the module availability information to each of the symbols availability mixin.

Tests/SwiftDocCTests/Rendering/SymbolAvailabilityTests.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2024 Apple Inc. and the Swift project authors
+ Copyright (c) 2024-2025 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
@@ -45,6 +45,7 @@ class SymbolAvailabilityTests: XCTestCase {
     private func renderNodeAvailability(
         defaultAvailability: [DefaultAvailability.ModuleAvailability] = [],
         symbolGraphOperatingSystemPlatformName: String,
+        symbolGraphEnvironmentName: String? = nil,
         symbols: [SymbolGraph.Symbol],
         symbolName: String
     ) throws -> [AvailabilityRenderItem] {
@@ -56,7 +57,7 @@ class SymbolAvailabilityTests: XCTestCase {
                 ]),
                 JSONFile(name: "ModuleName.symbols.json", content: makeSymbolGraph(
                     moduleName: "ModuleName",
-                    platform: SymbolGraph.Platform(architecture: nil, vendor: nil, operatingSystem: SymbolGraph.OperatingSystem(name: symbolGraphOperatingSystemPlatformName), environment: nil),
+                    platform: SymbolGraph.Platform(architecture: nil, vendor: nil, operatingSystem: SymbolGraph.OperatingSystem(name: symbolGraphOperatingSystemPlatformName), environment: symbolGraphEnvironmentName),
                     symbols: symbols,
                     relationships: []
                 )),
@@ -71,7 +72,7 @@ class SymbolAvailabilityTests: XCTestCase {
 
     func testSymbolGraphSymbolWithoutDeprecatedVersionAndIntroducedVersion() throws {
 
-        let availability = try renderNodeAvailability(
+        var availability = try renderNodeAvailability(
             defaultAvailability: [],
             symbolGraphOperatingSystemPlatformName: "ios",
             symbols: [
@@ -91,6 +92,34 @@ class SymbolAvailabilityTests: XCTestCase {
             "iPadOS <nil> - 1.2.3",
             "Mac Catalyst <nil> - 1.2.3",
         ])
+        
+        availability = try renderNodeAvailability(
+            defaultAvailability: [
+                DefaultAvailability.ModuleAvailability(platformName: PlatformName(operatingSystemName: "iOS"), platformVersion: "1.2.3")
+            ],
+            symbolGraphOperatingSystemPlatformName: "ios",
+            symbolGraphEnvironmentName: "macabi",
+            symbols: [
+                makeSymbol(
+                    id: "platform-1-symbol",
+                    kind: .class,
+                    pathComponents: ["SymbolName"],
+                    availability: [
+                        makeAvailabilityItem(domainName: "iOS", deprecated: SymbolGraph.SemanticVersion(string: "1.2.3")),
+                        makeAvailabilityItem(domainName: "visionOS", deprecated: SymbolGraph.SemanticVersion(string: "1.0.0"))
+                    ]
+                )
+            ],
+            symbolName: "SymbolName"
+        )
+        
+        XCTAssertEqual(availability.map { "\($0.name ?? "<nil>") \($0.introduced ?? "<nil>") - \($0.deprecated ?? "<nil>")" }, [
+            // The default availability for iOS shouldnt be copied to visionOS.
+            "iOS 1.2.3 - 1.2.3",
+            "iPadOS 1.2.3 - <nil>",
+            "Mac Catalyst 1.2.3 - 1.2.3",
+            "visionOS <nil> - 1.0",
+        ])
     }
 
     func testSymbolGraphSymbolWithObsoleteVersion() throws {