From 99f53dc12e7a9711c05358f0ab86ae8e41c69f2d Mon Sep 17 00:00:00 2001
From: Owen Voorhees <ovoorhees@apple.com>
Date: Tue, 8 Apr 2025 10:25:53 -0700
Subject: [PATCH] Initialize Swift Build with a toolchain-based developer
 directory

---
 .../SwiftBuildSupport/SwiftBuildSystem.swift  | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/Sources/SwiftBuildSupport/SwiftBuildSystem.swift b/Sources/SwiftBuildSupport/SwiftBuildSystem.swift
index 9127648ce3f..3f96e7075ca 100644
--- a/Sources/SwiftBuildSupport/SwiftBuildSystem.swift
+++ b/Sources/SwiftBuildSupport/SwiftBuildSystem.swift
@@ -62,13 +62,22 @@ func withService(
 func withSession(
     service: SWBBuildService,
     name: String,
+    toolchainPath: String,
     packageManagerResourcesDirectory: Basics.AbsolutePath?,
     body: @escaping (
         _ session: SWBBuildServiceSession,
         _ diagnostics: [SwiftBuild.SwiftBuildMessage.DiagnosticInfo]
     ) async throws -> Void
 ) async throws {
-    switch await service.createSession(name: name, resourceSearchPaths: packageManagerResourcesDirectory.map { [$0.pathString] } ?? [], cachePath: nil, inferiorProductsPath: nil, environment: nil) {
+    switch await service.createSession(
+        name: name,
+        swiftToolchainPath: toolchainPath,
+        resourceSearchPaths: packageManagerResourcesDirectory.map {
+            [$0.pathString]
+        } ?? [],
+        cachePath: nil, inferiorProductsPath: nil,
+        environment: nil
+    ) {
     case (.success(let session), let diagnostics):
         do {
             try await body(session, diagnostics)
@@ -265,7 +274,16 @@ public final class SwiftBuildSystem: SPMBuildCore.BuildSystem {
             )
 
             do {
-                try await withSession(service: service, name: self.buildParameters.pifManifest.pathString, packageManagerResourcesDirectory: self.packageManagerResourcesDirectory) { session, _ in
+                let toolchainPath = self.buildParameters.toolchain.swiftCompilerPath
+                    .parentDirectory // remove swift
+                    .parentDirectory // remove bin
+                    .parentDirectory // remove usr
+                try await withSession(
+                    service: service,
+                    name: self.buildParameters.pifManifest.pathString,
+                    toolchainPath: toolchainPath.pathString,
+                    packageManagerResourcesDirectory: self.packageManagerResourcesDirectory
+                ) { session, _ in
                     self.outputStream.send("Building for \(self.buildParameters.configuration == .debug ? "debugging" : "production")...\n")
 
                     // Load the workspace, and set the system information to the default