Allow linking _Concurrency for WASI with Embedded Swift (#1863)

Currently, when building packages for WASI with Embedded Swift, libraries such as `libswift_Concurrency.a` and `libswift_ConcurrencyDefaultExecutor.a` are not discoverable and require passing `-Xlinker <swift-sdk-path>/usr/lib/swift/embedded/wasm32-unknown-wasip1` option manually. This path can be inferred by the driver, which simplifies build invocations for users significantly, while the rest of linkage options (`-lswift_Concurrency` etc) can be specified in toolset files.

Author: MaxDesiatov

Sources/SwiftDriver/Jobs/WebAssemblyToolchain+LinkerSupport.swift

@@ -125,10 +125,17 @@ extension WebAssemblyToolchain {
         commandLine.appendPath(path)
       }
 
-      if !parsedOptions.isEmbeddedEnabled {
+      let runtimeResourcePath = VirtualPath.lookup(targetInfo.runtimeResourcePath.path)
+      if parsedOptions.isEmbeddedEnabled {
+        // Allow linking certain standard library modules (`_Concurrency` etc)
+        let embeddedLibrariesPath: VirtualPath = runtimeResourcePath.appending(
+          components: "embedded", targetTriple.triple
+        )
+        commandLine.append(.flag("-Xlinker"))
+        commandLine.append(.joinedOptionAndPath("-L", embeddedLibrariesPath))
+      } else {
         // Link the standard library and dependencies.
-        let linkFilePath: VirtualPath =
-        VirtualPath.lookup(targetInfo.runtimeResourcePath.path)
+        let linkFilePath: VirtualPath = runtimeResourcePath
           .appending(components: targetTriple.platformName() ?? "",
                      "static-executable-args.lnk")
         guard try fileSystem.exists(linkFilePath) else {

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -6890,16 +6890,25 @@ final class SwiftDriverTests: XCTestCase {
     do {
       for tripleEnv in ["wasi", "wasi-wasm", "wasip1", "wasip1-wasm", "wasip1-threads"] {
         var driver = try Driver(
-          args: ["swiftc", "-target", "wasm32-unknown-\(tripleEnv)", "test.o", "-enable-experimental-feature", "Embedded", "-wmo", "-o", "a.wasm"],
+          args: [
+            "swiftc", "-target", "wasm32-unknown-\(tripleEnv)",
+            "-resource-dir", "/usr/lib/swift",
+            "-enable-experimental-feature", "Embedded", "-wmo",
+            "test.o", "-o",  "a.wasm"
+          ],
           env: env
         )
         let plannedJobs = try driver.planBuild()
         XCTAssertEqual(plannedJobs.count, 1)
         let linkJob = plannedJobs[0]
+        print(linkJob.commandLine)
         XCTAssertFalse(linkJob.commandLine.contains(.flag("-force_load")))
         XCTAssertFalse(linkJob.commandLine.contains(.flag("-rpath")))
         XCTAssertFalse(linkJob.commandLine.contains(.flag("-lswiftCore")))
         XCTAssertFalse(linkJob.commandLine.joinedUnresolvedArguments.contains("swiftrt.o"))
+        XCTAssertTrue(linkJob.commandLine.contains(
+          .joinedOptionAndPath("-L", try .init(path: "/usr/lib/swift/embedded/wasm32-unknown-\(tripleEnv)"))
+        ))
       }
     }