From 7da61148f33c8f0c26bcdbffeacc511ec50a7b36 Mon Sep 17 00:00:00 2001
From: Kabir Oberai <oberai.kabir@gmail.com>
Date: Mon, 25 May 2026 05:55:37 -0400
Subject: [PATCH] SWBBuild SDK support

---
 Sources/XToolSupport/SDKBuilder.swift | 72 +++++++++++++++++++++++----
 1 file changed, 61 insertions(+), 11 deletions(-)

diff --git a/Sources/XToolSupport/SDKBuilder.swift b/Sources/XToolSupport/SDKBuilder.swift
index 44fc8fb..04000da 100644
--- a/Sources/XToolSupport/SDKBuilder.swift
+++ b/Sources/XToolSupport/SDKBuilder.swift
@@ -136,6 +136,9 @@ struct SDKBuilder {
             "linker": {
                 "path": "ld64.lld"
             },
+            "librarian": {
+                "path": "llvm-lib"
+            },
             "swiftCompiler": {
                 "extraCLIOptions": [
                     "-Xfrontend", "-enable-cross-import-overlays",
@@ -149,6 +152,24 @@ struct SDKBuilder {
             encoding: .utf8
         )
 
+        // this toolset works with the swiftbuild system
+        try """
+        {
+            "schemaVersion": "1.0",
+            "rootPath": "toolset/bin",
+            "linker": {
+                "path": "ld"
+            },
+            "librarian": {
+                "path": "llvm-lib"
+            }
+        }
+        """.write(
+            to: output.appendingPathComponent("toolset-swb.json"),
+            atomically: false,
+            encoding: .utf8
+        )
+
         let sdkDefinition = SDKDefinition(
             schemaVersion: "4.0",
             targetTriples: [
@@ -215,6 +236,16 @@ struct SDKBuilder {
             try await input.finish()
         }
         .checkSuccess()
+
+        // swift-build assumes we have an Apple-flavored librarian for Apple platforms
+        // (https://github.com/swiftlang/swift-build/blob/b2433e74e/Sources/SWBCore/SpecImplementations/Tools/LinkerTools.swift#L1735)
+        // but allows us to override this assumption if we explicitly provide the name llvm-lib (look a few lines above in that file)
+        try FileManager.default.moveItem(
+            at: toolsetDir.appending(path: "bin/libtool"),
+            to: toolsetDir.appending(path: "bin/llvm-lib")
+        )
+
+        // TODO: install cctools ld as well
     }
 
     // swiftlint:disable:next cyclomatic_complexity
@@ -321,10 +352,11 @@ struct SDKBuilder {
 
         for platform in ["iPhoneOS", "MacOSX", "iPhoneSimulator"] {
             let lib = "../../../../../Library"
-            let dest = dev.appendingPathComponent("""
-            Platforms/\(platform).platform/Developer/SDKs/\(platform).sdk\
-            /System/Library/Frameworks
-            """).path
+            let sdkDir = dev.appending(path: "Platforms/\(platform).platform/Developer/SDKs/\(platform).sdk")
+
+            try patchSDKSettings(path: sdkDir.appending(path: "SDKSettings.plist"))
+
+            let dest = sdkDir.appending(path: "System/Library/Frameworks").path
 
             try FileManager.default.createSymbolicLink(
                 atPath: "\(dest)/Testing.framework",
@@ -354,6 +386,21 @@ struct SDKBuilder {
         return dev
     }
 
+    private func patchSDKSettings(path: URL) throws {
+        let data = try Data(contentsOf: path)
+        guard var plist = try PropertyListSerialization.propertyList(from: data, options: [], format: nil) as? [String: Any] else {
+            throw Console.Error("Could not read SDKSettings.plist at '\(path.path)'")
+        }
+
+        var customProperties = (plist["CustomProperties"] as? [String: Any]) ?? [:]
+        customProperties["SWIFT_RESOURCE_DIR"] = "$(PLATFORM_DIR)/../../Toolchains/XcodeDefault.xctoolchain/usr/lib/swift"
+        customProperties["CLANG_RESOURCE_DIR"] = "$(SYSTEM_DEVELOPER_USR_DIR)/lib/swift/clang"
+        plist["CustomProperties"] = customProperties
+
+        let newData = try PropertyListSerialization.data(fromPropertyList: plist, format: .xml, options: 0)
+        try newData.write(to: path)
+    }
+
     // returns the number of files we actually want to keep,
     // useful for computing progress % during fs traversal
     private func extractXIP(inputPath: String, outDir: String) async throws -> Int {
@@ -497,13 +544,16 @@ struct SDKEntry {
             E("clang"),
         ]),
         E("Platforms", ["iPhoneOS", "MacOSX", "iPhoneSimulator"].map {
-            E("\($0).platform/Developer", [
-                E("SDKs"),
-                E("Library", [
-                    E("Frameworks"),
-                    E("PrivateFrameworks"),
-                ]),
-                E("usr/lib"),
+            E("\($0).platform", [
+                E("Info.plist"),
+                E("Developer", [
+                    E("SDKs"),
+                    E("Library", [
+                        E("Frameworks"),
+                        E("PrivateFrameworks"),
+                    ]),
+                    E("usr/lib"),
+                ])
             ])
         }),
     ])