Support Swift SDKs

package.json

@@ -599,9 +599,15 @@
           "swift.SDK": {
             "type": "string",
             "default": "",
-            "markdownDescription": "The path of the SDK to compile against (`--sdk` parameter). This is of use when supporting non-standard SDK layouts on Windows and using custom SDKs. The default SDK is determined by the environment on macOS and Windows.",
+            "markdownDescription": "The path of the SDK to compile against (`--sdk` parameter). This is of use when supporting non-standard SDK layouts on Windows and using custom SDKs. The default SDK is determined by the environment on macOS and Windows.\n\nFor SwiftPM projects, prefer using `swift.swiftSDK` with a triple (such as `arm64-apple-ios`) or Swift SDK name instead.",
             "order": 3
           },
+          "swift.swiftSDK": {
+            "type": "string",
+            "default": "",
+            "markdownDescription": "The [Swift SDK](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0387-cross-compilation-destinations.md) to compile against (`--swift-sdk` parameter).",
+            "order": 4
+          },
           "swift.diagnostics": {
             "type": "boolean",
             "default": false,

src/configuration.ts

@@ -190,13 +190,20 @@ const configuration = {
     get runtimePath(): string {
         return vscode.workspace.getConfiguration("swift").get<string>("runtimePath", "");
     },
-    /** Path to custom swift sdk */
+    /** Path to custom --sdk */
     get sdk(): string {
         return vscode.workspace.getConfiguration("swift").get<string>("SDK", "");
     },
     set sdk(value: string | undefined) {
         vscode.workspace.getConfiguration("swift").update("SDK", value);
     },
+    /** Path to custom --swift-sdk */
+    get swiftSDK(): string {
+        return vscode.workspace.getConfiguration("swift").get<string>("swiftSDK", "");
+    },
+    set swiftSDK(value: string | undefined) {
+        vscode.workspace.getConfiguration("swift").update("swiftSDK", value);
+    },
     /** swift build arguments */
     get buildArguments(): string[] {
         return vscode.workspace.getConfiguration("swift").get<string[]>("buildArguments", []);

src/extension.ts

@@ -98,7 +98,10 @@ export async function activate(context: vscode.ExtensionContext): Promise<Api> {
                     );
                 }
                 // on sdk config change, restart sourcekit-lsp
-                if (event.affectsConfiguration("swift.SDK")) {
+                if (
+                    event.affectsConfiguration("swift.SDK") ||
+                    event.affectsConfiguration("swift.swiftSDK")
+                ) {
                     // FIXME: There is a bug stopping us from restarting SourceKit-LSP directly.
                     // As long as it's fixed we won't need to reload on newer versions.
                     showReloadExtensionNotification(

src/sourcekit-lsp/LanguageClientManager.ts

@@ -641,6 +641,14 @@ export class LanguageClientManager implements vscode.Disposable {
                 backgroundPreparationMode: "enabled",
             };
         }
+
+        if (configuration.swiftSDK !== "") {
+            options = {
+                ...options,
+                swiftPM: { swiftSDK: configuration.swiftSDK },
+            };
+        }
+
         return options;
     }
 

src/toolchain/BuildFlags.ts

@@ -73,10 +73,14 @@ export class BuildFlags {
      * Get SDK flags for SwiftPM
      */
     swiftpmSDKFlags(): string[] {
+        const flags: string[] = [];
         if (configuration.sdk !== "") {
-            return ["--sdk", configuration.sdk, ...this.swiftDriverTargetFlags(true)];
+            flags.push("--sdk", configuration.sdk, ...this.swiftDriverTargetFlags(true));
         }
-        return [];
+        if (configuration.swiftSDK !== "") {
+            flags.push("--swift-sdk", configuration.swiftSDK);
+        }
+        return flags;
     }
 
     /**

test/unit-tests/sourcekit-lsp/LanguageClientManager.test.ts

@@ -187,6 +187,25 @@ suite("LanguageClientManager Suite", () => {
         expect(languageClientMock.start).to.have.been.calledOnce;
     });
 
+    test("launches SourceKit-LSP on startup with swiftSDK", async () => {
+        mockedConfig.swiftSDK = "arm64-apple-ios";
+
+        const sut = new LanguageClientManager(instance(mockedWorkspace), languageClientFactoryMock);
+        await waitForReturnedPromises(languageClientMock.start);
+
+        expect(sut.state).to.equal(State.Running);
+        expect(languageClientFactoryMock.createLanguageClient).to.have.been.calledOnceWith(
+            /* id */ match.string,
+            /* name */ match.string,
+            /* serverOptions */ match.has("command", "/path/to/toolchain/bin/sourcekit-lsp"),
+            /* clientOptions */ match.hasNested(
+                "initializationOptions.swiftPM.swiftSDK",
+                "arm64-apple-ios"
+            )
+        );
+        expect(languageClientMock.start).to.have.been.calledOnce;
+    });
+
     test("chooses the correct backgroundIndexing value is auto, swift version if 6.0.0", async () => {
         mockedWorkspace.swiftVersion = new Version(6, 0, 0);
         mockedConfig.backgroundIndexing = "auto";

test/unit-tests/toolchain/BuildFlags.test.ts

@@ -78,9 +78,11 @@ suite("BuildFlags Test Suite", () => {
 
     suite("swiftpmSDKFlags", () => {
         const sdkConfig = mockGlobalValue(configuration, "sdk");
+        const swiftSDKConfig = mockGlobalValue(configuration, "swiftSDK");
 
         test("no configuration provided", async () => {
             sdkConfig.setValue("");
+            swiftSDKConfig.setValue("");
             expect(buildFlags.swiftpmSDKFlags()).to.be.an("array").that.is.empty;
         });
 
@@ -92,6 +94,22 @@ suite("BuildFlags Test Suite", () => {
             ]);
         });
 
+        test("configuration provided for swiftSDK", () => {
+            swiftSDKConfig.setValue("arm64-apple-ios");
+            expect(buildFlags.swiftpmSDKFlags()).to.deep.equal(["--swift-sdk", "arm64-apple-ios"]);
+        });
+
+        test("configuration provided for swiftSDK and sdk", () => {
+            sdkConfig.setValue("/some/other/full/test/path");
+            swiftSDKConfig.setValue("arm64-apple-ios");
+            expect(buildFlags.swiftpmSDKFlags()).to.deep.equal([
+                "--sdk",
+                "/some/other/full/test/path",
+                "--swift-sdk",
+                "arm64-apple-ios",
+            ]);
+        });
+
         test("include target", () => {
             sdkConfig.setValue("/some/other/full/test/path/WatchOS.sdk");
             expect(buildFlags.swiftpmSDKFlags()).to.deep.equal([