Improve resolveBuildProducts performance

Sources/ScipioKit/DescriptionPackage.swift

@@ -149,6 +149,50 @@ struct DescriptionPackage {
 }
 
 extension DescriptionPackage {
+    func resolveBuildProducts() throws -> [BuildProduct] {
+    }
+}
+
+struct BuildProduct: Hashable, Sendable {
+    var package: ResolvedPackage
+    var target: ScipioResolvedModule
+
+    var frameworkName: String {
+        "\(target.name.packageNamed()).xcframework"
+    }
+
+    var binaryTarget: ScipioBinaryModule? {
+        target.underlying as? ScipioBinaryModule
+    }
+
+    func hash(into hasher: inout Hasher) {
+        // Important: Relevant for swift-6.0+ toolchain versions. For the versions below
+        // this change has no effect as SwiftPM provides its own proper `Hashable`
+        // implementations for both `ResolvedPackage` and `ResolvedTarget`.
+        //
+        // We cannot directly use `ResolvedModule.id` here as `id` also includes `BuildTriple`.
+        // The reason for this is that `ResolvedModule.buildTriple` is parent-dependent; more
+        // specifically, the same `ResolvedModule` will have a different build triple depending
+        // on whether it is in a root or dependency position.
+        // For more context, see `ResolvedModule.updateBuildTriplesOfDependencies`.
+        //
+        // At the same time, build triples remain irrelevant for the `Scipio` use case where the
+        // build product must be the same regardless of the triple. Meanwhile, the target name and
+        // package identity remain relevant and unambiguously identify the build product.
+        hasher.combine(target.name)
+        hasher.combine(package.identity)
+    }
+}
+
+
+private final class BuildProductsResolver {
+    private var visitedTargets: Set<ResolvedTarget> = []
+    let descriptionPackage: DescriptionPackage
+
+    init(descriptionPackage: DescriptionPackage) {
+        self.descriptionPackage = descriptionPackage
+    }
+
     func resolveBuildProducts() throws -> [BuildProduct] {
         let targetsToBuild = try targetsToBuild()
         var products = try targetsToBuild.flatMap(resolveBuildProduct(from:))
@@ -254,34 +298,3 @@ extension DescriptionPackage {
         return Set([rootTargetProduct] + dependencyProducts)
     }
 }
-
-struct BuildProduct: Hashable, Sendable {
-    var package: ResolvedPackage
-    var target: ScipioResolvedModule
-
-    var frameworkName: String {
-        "\(target.name.packageNamed()).xcframework"
-    }
-
-    var binaryTarget: ScipioBinaryModule? {
-        target.underlying as? ScipioBinaryModule
-    }
-
-    func hash(into hasher: inout Hasher) {
-        // Important: Relevant for swift-6.0+ toolchain versions. For the versions below
-        // this change has no effect as SwiftPM provides its own proper `Hashable`
-        // implementations for both `ResolvedPackage` and `ResolvedTarget`.
-        //
-        // We cannot directly use `ResolvedModule.id` here as `id` also includes `BuildTriple`.
-        // The reason for this is that `ResolvedModule.buildTriple` is parent-dependent; more
-        // specifically, the same `ResolvedModule` will have a different build triple depending
-        // on whether it is in a root or dependency position.
-        // For more context, see `ResolvedModule.updateBuildTriplesOfDependencies`.
-        //
-        // At the same time, build triples remain irrelevant for the `Scipio` use case where the 
-        // build product must be the same regardless of the triple. Meanwhile, the target name and
-        // package identity remain relevant and unambiguously identify the build product.
-        hasher.combine(target.name)
-        hasher.combine(package.identity)
-    }
-}