Fix setting SPECIALIZATION_SDK_OPTIONS, .ARCHS

Fixtures/PIFBuilder/PackageWithSDKSpecialization/Package.swift

@@ -0,0 +1,23 @@
+// swift-tools-version: 6.2
+
+import PackageDescription
+
+let package = Package(
+    name: "PackageWithSDKSpecialization",
+    platforms: [ .macOS("10.15.foo") ],
+    products: [
+        .library(
+            name: "PackageWithSDKSpecialization",
+            targets: ["PackageWithSDKSpecialization"]),
+    ],
+    targets: [
+        .target(
+            name: "PackageWithSDKSpecialization",
+            dependencies: []
+        ),
+        .target(
+            name: "Executable",
+            dependencies: ["PackageWithSDKSpecialization"]
+        ),
+    ]
+)

Fixtures/PIFBuilder/PackageWithSDKSpecialization/Sources/Executable/main.swift

@@ -0,0 +1 @@
+print("Hello, world!")

Fixtures/PIFBuilder/PackageWithSDKSpecialization/Sources/PackageWithSDKSpecialization/PackageWithSDKSpecialization.swift

@@ -0,0 +1,3 @@
+struct PackageWithSDKSpecialization {
+    var text = "Hello, World!"
+}

Sources/SwiftBuildSupport/PackagePIFBuilder.swift

@@ -581,7 +581,7 @@ public final class PackagePIFBuilder {
                 log(.warning, "Ignoring options '\(platformOptions.joined(separator: " "))' specified for unknown platform \(platform.name)")
                 continue
             }
-            settings[.SPECIALIZATION_SDK_OPTIONS, pifPlatform]?.append(contentsOf: platformOptions)
+            settings[.SPECIALIZATION_SDK_OPTIONS, pifPlatform] = (settings[.SPECIALIZATION_SDK_OPTIONS, pifPlatform] ?? []) + platformOptions
         }
 
         let deviceFamilyIDs: Set<Int> = self.delegate.deviceFamilyIDs()
@@ -607,7 +607,7 @@ public final class PackagePIFBuilder {
                 } catch {
                     preconditionFailure("Unhandled arm64e platform: \(error)")
                 }
-                settings[.ARCHS, pifPlatform]?.append(contentsOf: ["arm64e"])
+                settings[.ARCHS, pifPlatform] = (settings[.ARCHS, pifPlatform] ?? []) + ["arm64e"]
             }
         }
 

Tests/SwiftBuildSupportTests/PIFBuilderTests.swift

@@ -118,6 +118,19 @@ extension SwiftBuildSupport.PIF.Project {
             throw StringError("Multiple targets named \(name) in PIF project")
         }
     }
+
+    fileprivate func buildConfig(named name: String) throws -> SwiftBuild.ProjectModel.BuildConfig {
+        let matchingConfigs = underlying.buildConfigs.filter {
+            $0.name == name
+        }
+        if matchingConfigs.isEmpty {
+            throw StringError("No config named \(name) in PIF project")
+        } else if matchingConfigs.count > 1 {
+            throw StringError("Multiple configs named \(name) in PIF project")
+        } else {
+            return matchingConfigs[0]
+        }
+    }
 }
 
 extension SwiftBuild.ProjectModel.BaseTarget {
@@ -177,6 +190,19 @@ struct PIFBuilderTests {
         }
     }
 
+    @Test func packageWithInternal() async throws {
+        try await withGeneratedPIF(fromFixture: "PIFBuilder/PackageWithSDKSpecialization") { pif, observabilitySystem in
+            let errors = observabilitySystem.diagnostics.filter { $0.severity == .error }
+            #expect(errors.isEmpty, "Expected no errors during PIF generation, but got: \(errors)")
+
+            let releaseConfig = try pif.workspace
+                .project(named: "PackageWithSDKSpecialization")
+                .buildConfig(named: "Release")
+
+            #expect(releaseConfig.settings[.SPECIALIZATION_SDK_OPTIONS, .macOS] == ["foo"])
+        }
+    }
+
     @Test func pluginWithBinaryTargetDependency() async throws {
         try await withGeneratedPIF(fromFixture: "Miscellaneous/Plugins/BinaryTargetExePlugin") { pif, observabilitySystem in
             // Verify that PIF generation succeeds for a package with a plugin that depends on a binary target