Infer properties of derived test target. (#7041)

Right now, when we construct the derived test target used on
Linux/Windows with corelibs-xctest, we don't preserve the `platforms`
property. The toolchain then infers a value for it based on the current
OS. Since Swift doesn't currently support versioning on those platforms,
the end result is the same.

However, if we want to start using a derived test target with
swift-testing on Apple platforms, we need to propagate this information
correctly. This PR does that.

Author: grynspan

Sources/Build/BuildPlan/BuildPlan+Test.swift

@@ -86,8 +86,8 @@ extension BuildPlan {
                 let discoveryResolvedTarget = ResolvedTarget(
                     target: discoveryTarget,
                     dependencies: testProduct.targets.map { .target($0, conditions: []) },
-                    defaultLocalization: .none, // safe since this is a derived target
-                    platforms: .init(declared: [], derivedXCTestPlatformProvider: .none) // safe since this is a derived target
+                    defaultLocalization: testProduct.defaultLocalization,
+                    platforms: testProduct.platforms
                 )
                 let discoveryTargetBuildDescription = try SwiftTargetBuildDescription(
                     package: package,
@@ -119,8 +119,8 @@ extension BuildPlan {
                 let entryPointResolvedTarget = ResolvedTarget(
                     target: entryPointTarget,
                     dependencies: testProduct.targets.map { .target($0, conditions: []) } + [.target(discoveryResolvedTarget, conditions: [])],
-                    defaultLocalization: .none, // safe since this is a derived target
-                    platforms: .init(declared: [], derivedXCTestPlatformProvider: .none) // safe since this is a derived target
+                    defaultLocalization: testProduct.defaultLocalization,
+                    platforms: testProduct.platforms
                 )
                 return try SwiftTargetBuildDescription(
                     package: package,
@@ -148,8 +148,8 @@ extension BuildPlan {
                         let entryPointResolvedTarget = ResolvedTarget(
                             target: entryPointTarget,
                             dependencies: entryPointResolvedTarget.dependencies + [.target(discoveryTargets.resolved, conditions: [])],
-                            defaultLocalization: .none, // safe since this is a derived target
-                            platforms: .init(declared: [], derivedXCTestPlatformProvider: .none) // safe since this is a derived target
+                            defaultLocalization: testProduct.defaultLocalization,
+                            platforms: testProduct.platforms
                         )
                         let entryPointTargetBuildDescription = try SwiftTargetBuildDescription(
                             package: package,

Sources/PackageGraph/ResolvedProduct.swift

@@ -59,6 +59,14 @@ public final class ResolvedProduct {
         self.underlyingProduct = product
         self.targets = targets
 
+        // defaultLocalization is currently shared across the entire package
+        // this may need to be enhanced if / when we support localization per target or product
+        let defaultLocalization = self.targets.first?.defaultLocalization
+        self.defaultLocalization = defaultLocalization
+
+        let platforms = Self.computePlatforms(targets: targets)
+        self.platforms = platforms
+
         self.testEntryPointTarget = underlyingProduct.testEntryPointPath.map { testEntryPointPath in
             // Create an executable resolved target with the entry point file, adding product's targets as dependencies.
             let dependencies: [Target.Dependency] = product.targets.map { .target($0, conditions: []) }
@@ -69,16 +77,10 @@ public final class ResolvedProduct {
             return ResolvedTarget(
                 target: swiftTarget,
                 dependencies: targets.map { .target($0, conditions: []) },
-                defaultLocalization: .none, // safe since this is a derived product
-                platforms: .init(declared: [], derivedXCTestPlatformProvider: .none) // safe since this is a derived product
+                defaultLocalization: defaultLocalization ?? .none, // safe since this is a derived product
+                platforms: platforms
             )
         }
-
-        // defaultLocalization is currently shared across the entire package
-        // this may need to be enhanced if / when we support localization per target or product
-        self.defaultLocalization = self.targets.first?.defaultLocalization
-
-        self.platforms = Self.computePlatforms(targets: targets)
     }
 
     /// True if this product contains Swift targets.