WasmSDK: Copy swift-foundation headers and apinotes into the Swift SDK bundle (#129)

* WasmSDK: Copy swift-foundation headers and apinotes into the Swift SDK bundle

Those files are recently added to the toolchain, and they are required
to build Swift code that uses Foundation on WebAssembly.

We had been manually specifying the paths to copy from the target
package into the SDK, but we now build host-agnostic SDKS.
So we can just copy the whole `usr/lib` from the target Swift package
into the SDK bundle instead of adding individual new paths.
The host-specific build path is still used for 5.10 SDKs, so keep the
old code as is for now, but it will be removed in the future.

* Create swift.xctoolchain/usr directory before copying target package

---------

Co-authored-by: Max Desiatov <[email protected]>

Author: kateinoigakukun

Sources/SwiftSDKGenerator/SwiftSDKRecipes/WebAssemblyRecipe.swift

@@ -94,6 +94,8 @@ public struct WebAssemblyRecipe: SwiftSDKRecipe {
     httpClient: some HTTPClientProtocol
   ) async throws -> SwiftSDKProduct {
     let pathsConfiguration = generator.pathsConfiguration
+    let targetSwiftLibPath = self.targetSwiftPackagePath.appending("usr/lib")
+
     logGenerationStep("Copying Swift binaries for the host triple...")
     var hostTriples: [Triple]? = nil
     if let hostSwiftPackage {
@@ -117,10 +119,14 @@ public struct WebAssemblyRecipe: SwiftSDKRecipe {
         libraries: unusedHostLibraries + liblldbNames,
         binaries: unusedHostBinaries + ["lldb", "lldb-argdumper", "lldb-server"]
       )
+      // Merge target Swift package with the host package.
+      try await self.mergeTargetSwift(from: targetSwiftLibPath, generator: generator)
+    } else {
+      // Simply copy the target Swift package into the SDK bundle when building host-agnostic SDK.
+      try await generator.createDirectoryIfNeeded(at: pathsConfiguration.toolchainDirPath.appending("usr"))
+      try await generator.copy(from: targetSwiftLibPath, to: pathsConfiguration.toolchainDirPath.appending("usr/lib"))
     }
 
-    try await self.copyTargetSwift(from: self.targetSwiftPackagePath.appending("usr/lib"), generator: generator)
-
     let autolinkExtractPath = generator.pathsConfiguration.toolchainBinDirPath.appending("swift-autolink-extract")
 
     // WebAssembly object file requires `swift-autolink-extract`
@@ -138,7 +144,8 @@ public struct WebAssemblyRecipe: SwiftSDKRecipe {
     return SwiftSDKProduct(sdkDirPath: sdkDirPath, hostTriples: hostTriples)
   }
 
-  func copyTargetSwift(from distributionPath: FilePath, generator: SwiftSDKGenerator) async throws {
+  /// Merge the target Swift package into the Swift SDK bundle derived from the host Swift package.
+  func mergeTargetSwift(from distributionPath: FilePath, generator: SwiftSDKGenerator) async throws {
     let pathsConfiguration = generator.pathsConfiguration
     logGenerationStep("Copying Swift core libraries for the target triple into Swift SDK bundle...")
     for (pathWithinPackage, pathWithinSwiftSDK, isOptional) in [