Drop unknown platforms when generating PIF

Author: owenv

Fixtures/PIFBuilder/UnknownPlatforms/Package.swift

@@ -0,0 +1,17 @@
+// swift-tools-version: 6.2
+
+import PackageDescription
+
+let package = Package(
+    name: "UnknownPlatforms",
+    targets: [
+        .executableTarget(
+            name: "UnknownPlatforms",
+            swiftSettings: [
+                .define("FOO", .when(platforms: [.custom("DoesNotExist")])),
+		.define("BAR", .when(platforms: [.linux])),
+                .define("BAZ", .when(platforms: [.macOS])),
+            ],
+        ),
+    ]
+)

Fixtures/PIFBuilder/UnknownPlatforms/Sources/UnknownPlatforms/UnknownPlatforms.swift

@@ -0,0 +1,9 @@
+// The Swift Programming Language
+// https://docs.swift.org/swift-book
+
+@main
+struct UnknownPlatforms {
+    static func main() {
+        print("Hello, world!")
+    }
+}

Sources/SwiftBuildSupport/PackagePIFBuilder+Helpers.swift

@@ -234,7 +234,7 @@ extension Sequence<PackageModel.PackageCondition> {
             }
 
             var pifPlatformsForCondition: [ProjectModel.BuildSettings.Platform] = platforms
-                .map { ProjectModel.BuildSettings.Platform(from: $0) }
+                .compactMap { try? ProjectModel.BuildSettings.Platform(from: $0) }
 
             // Treat catalyst like macOS for backwards compatibility with older tools versions.
             if pifPlatformsForCondition.contains(.macOS), toolsVersion < ToolsVersion.v5_5 {
@@ -537,7 +537,7 @@ extension PackageGraph.ResolvedModule {
     /// Collect the build settings defined in the package manifest.
     /// Some of them apply *only* to the target itself, while others are also imparted to clients.
     /// Note that the platform is *optional*; unconditional settings have no platform condition.
-    var allBuildSettings: AllBuildSettings {
+    func computeAllBuildSettings(observabilityScope: ObservabilityScope) -> AllBuildSettings {
         var allSettings = AllBuildSettings()
 
         for (declaration, settingsAssigments) in self.underlying.buildSettings.assignments {
@@ -565,7 +565,16 @@ extension PackageGraph.ResolvedModule {
                 let (platforms, configurations, _) = settingAssignment.conditions.splitIntoConcreteConditions
 
                 for platform in platforms {
-                    let pifPlatform = platform.map { ProjectModel.BuildSettings.Platform(from: $0) }
+                    let pifPlatform: ProjectModel.BuildSettings.Platform?
+                    if let platform {
+                        guard let computedPifPlatform = try? ProjectModel.BuildSettings.Platform(from: platform) else {
+                            observabilityScope.logPIF(.warning, "Ignoring settings assignments for unknown platform '\(platform.name)'")
+                            continue
+                        }
+                        pifPlatform = computedPifPlatform
+                    } else {
+                        pifPlatform = nil
+                    }
 
                     if pifDeclaration == .OTHER_LDFLAGS {
                         var settingsByDeclaration: [ProjectModel.BuildSettings.Declaration: [String]]
@@ -962,7 +971,11 @@ extension ProjectModel.BuildSettings.MultipleValueSetting {
 }
 
 extension ProjectModel.BuildSettings.Platform {
-    init(from platform: PackageModel.Platform) {
+    enum Error: Swift.Error {
+        case unknownPlatform(String)
+    }
+
+    init(from platform: PackageModel.Platform) throws {
         self = switch platform {
         case .macOS: .macOS
         case .macCatalyst: .macCatalyst
@@ -977,7 +990,7 @@ extension ProjectModel.BuildSettings.Platform {
         case .wasi: .wasi
         case .openbsd: .openbsd
         case .freebsd: .freebsd
-        default: preconditionFailure("Unexpected platform: \(platform.name)")
+        default: throw Error.unknownPlatform(platform.name)
         }
     }
 }

Sources/SwiftBuildSupport/PackagePIFBuilder.swift

@@ -562,7 +562,10 @@ public final class PackagePIFBuilder {
         self.delegate.configureProjectBuildSettings(&settings)
 
         for (platform, platformOptions) in self.package.sdkOptions(delegate: self.delegate) {
-            let pifPlatform = ProjectModel.BuildSettings.Platform(from: platform)
+            guard let pifPlatform = try? ProjectModel.BuildSettings.Platform(from: platform) else {
+                log(.warning, "Ignoring options '\(platformOptions.joined(separator: " "))' specified for unknown platform \(platform.name)")
+                continue
+            }
             settings.platformSpecificSettings[pifPlatform]![.SPECIALIZATION_SDK_OPTIONS]!
                 .append(contentsOf: platformOptions)
         }
@@ -584,11 +587,11 @@ public final class PackagePIFBuilder {
         let arm64ePlatforms: [PackageModel.Platform] = [.iOS, .macOS, .visionOS]
         for arm64ePlatform in arm64ePlatforms {
             if self.delegate.shouldPackagesBuildForARM64e(platform: arm64ePlatform) {
-                let pifPlatform: ProjectModel.BuildSettings.Platform = switch arm64ePlatform {
-                case .iOS:
-                    ._iOSDevice
-                default:
-                    .init(from: arm64ePlatform)
+                let pifPlatform: ProjectModel.BuildSettings.Platform
+                do {
+                    pifPlatform = try .init(from: arm64ePlatform)
+                } catch {
+                    preconditionFailure("Unhandled arm64e platform: \(error)")
                 }
                 settings.platformSpecificSettings[pifPlatform]![.ARCHS, default: []].append(contentsOf: ["arm64e"])
             }

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Modules.swift

@@ -738,7 +738,7 @@ extension PackagePIFProjectBuilder {
         var debugSettings = settings
         var releaseSettings = settings
 
-        let allBuildSettings = sourceModule.allBuildSettings
+        let allBuildSettings = sourceModule.computeAllBuildSettings(observabilityScope: pifBuilder.observabilityScope)
 
         // Apply target-specific build settings defined in the manifest.
         for (buildConfig, declarationsByPlatform) in allBuildSettings.targetSettings {
@@ -756,7 +756,7 @@ extension PackagePIFProjectBuilder {
         }
 
         // Impart the linker flags.
-        for (platform, settingsByDeclaration) in sourceModule.allBuildSettings.impartedSettings {
+        for (platform, settingsByDeclaration) in sourceModule.computeAllBuildSettings(observabilityScope: pifBuilder.observabilityScope).impartedSettings {
             // Note: A `nil` platform means that the declaration applies to *all* platforms.
             for (declaration, stringValues) in settingsByDeclaration {
                 impartedSettings.append(values: stringValues, to: declaration, platform: platform)

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Products.swift

@@ -470,7 +470,7 @@ extension PackagePIFProjectBuilder {
         var releaseSettings: ProjectModel.BuildSettings = settings
 
         // Apply target-specific build settings defined in the manifest.
-        for (buildConfig, declarationsByPlatform) in mainModule.allBuildSettings.targetSettings {
+        for (buildConfig, declarationsByPlatform) in mainModule.computeAllBuildSettings(observabilityScope: pifBuilder.observabilityScope).targetSettings {
             for (platform, declarations) in declarationsByPlatform {
                 // A `nil` platform means that the declaration applies to *all* platforms.
                 for (declaration, stringValues) in declarations {