Add a method to lookup the identifier of a registered toolchain

Sources/SWBBuildService/Messages.swift

@@ -302,6 +302,14 @@ private struct SetSessionUserPreferencesMsg: MessageHandler {
     }
 }
 
+private struct LookupToolchainMsg: MessageHandler {
+    func handle(request: Request, message: LookupToolchainRequest) throws -> LookupToolchainResponse {
+        let session = try request.session(for: message)
+        let toolchain = try session.core.toolchainRegistry.lookup(path: message.path)
+        return LookupToolchainResponse(toolchainIdentifier: toolchain?.identifier)
+    }
+}
+
 /// Start a PIF transfer from the client.
 ///
 /// This will establish a workspace context in the relevant session by exchanging a PIF from the client to the service incrementally, only transferring subobjects as necessary.
@@ -1543,6 +1551,7 @@ public struct ServiceSessionMessageHandlers: ServiceExtension {
         service.registerMessageHandler(SetSessionUserInfoMsg.self)
         service.registerMessageHandler(SetSessionUserPreferencesMsg.self)
         service.registerMessageHandler(DeveloperPathHandler.self)
+        service.registerMessageHandler(LookupToolchainMsg.self)
     }
 }
 

Sources/SWBCore/ToolchainRegistry.swift

@@ -540,6 +540,16 @@ public final class ToolchainRegistry: @unchecked Sendable {
         }
     }
 
+    public func lookup(path: Path) throws -> Toolchain? {
+        let path = try self.fs.realpath(path)
+        for toolchain in toolchains {
+            if try self.fs.realpath(toolchain.path) == path {
+                return toolchain
+            }
+        }
+        return nil
+    }
+
     public var defaultToolchain: Toolchain? {
         return self.lookup("default")
     }

Sources/SWBProtocol/Message.swift

@@ -632,6 +632,31 @@ public struct SetSessionUserPreferencesRequest: SessionMessage, RequestMessage,
     }
 }
 
+public struct LookupToolchainRequest: SessionMessage, RequestMessage, Equatable, SerializableCodable {
+    public typealias ResponseMessage = LookupToolchainResponse
+
+    public static let name = "LOOKUP_TOOLCHAIN"
+
+    public let sessionHandle: String
+
+    public let path: Path
+
+    public init(sessionHandle: String, path: Path) {
+        self.sessionHandle = sessionHandle
+        self.path = path
+    }
+}
+
+public struct LookupToolchainResponse: Message, Equatable, SerializableCodable {
+    public static let name = "LOOKUP_TOOLCHAIN_RESPONSE"
+
+    public let toolchainIdentifier: String?
+
+    public init(toolchainIdentifier: String?) {
+        self.toolchainIdentifier = toolchainIdentifier
+    }
+}
+
 public struct ListSessionsRequest: RequestMessage, Equatable {
     public typealias ResponseMessage = ListSessionsResponse
 
@@ -1176,6 +1201,8 @@ public struct IPCMessage: Serializable, Sendable {
         SetSessionSystemInfoRequest.self,
         SetSessionUserInfoRequest.self,
         SetSessionUserPreferencesRequest.self,
+        LookupToolchainRequest.self,
+        LookupToolchainResponse.self,
         ListSessionsRequest.self,
         ListSessionsResponse.self,
         WaitForQuiescenceRequest.self,

Sources/SwiftBuild/SWBBuildServiceSession.swift

@@ -629,6 +629,14 @@ public final class SWBBuildServiceSession: Sendable {
     public func setUserPreferences(enableDebugActivityLogs: Bool, enableBuildDebugging: Bool, enableBuildSystemCaching: Bool, activityTextShorteningLevel: Int, usePerConfigurationBuildLocations: Bool?, allowsExternalToolExecution: Bool) async throws {
         _ = try await service.send(request: SetSessionUserPreferencesRequest(sessionHandle: self.uid, enableDebugActivityLogs: enableDebugActivityLogs, enableBuildDebugging: enableBuildDebugging, enableBuildSystemCaching: enableBuildSystemCaching, activityTextShorteningLevel: ActivityTextShorteningLevel(rawValue: activityTextShorteningLevel) ?? .default, usePerConfigurationBuildLocations: usePerConfigurationBuildLocations, allowsExternalToolExecution: allowsExternalToolExecution))
     }
+
+    public func lookupToolchain(at path: String) async throws -> SWBToolchainIdentifier? {
+        return try await service.send(request: LookupToolchainRequest(sessionHandle: self.uid, path: Path(path))).toolchainIdentifier.map { SWBToolchainIdentifier(rawValue: $0) }
+    }
+}
+
+public struct SWBToolchainIdentifier {
+    public var rawValue: String
 }
 
 extension SWBBuildServiceSession {

Sources/SwiftBuildTestSupport/TestUtilities.swift

@@ -37,11 +37,11 @@ package actor TestSWBSession {
     package nonisolated let sessionDiagnostics: [SwiftBuildMessage.DiagnosticInfo]
     private var closed = false
 
-    package init(connectionMode: SWBBuildServiceConnectionMode = .default, variant: SWBBuildServiceVariant = .default, temporaryDirectory: NamedTemporaryDirectory?) async throws {
+    package init(connectionMode: SWBBuildServiceConnectionMode = .default, variant: SWBBuildServiceVariant = .default, temporaryDirectory: NamedTemporaryDirectory?, environment: [String: String] = [:]) async throws {
         self.tmpDir = try temporaryDirectory ?? NamedTemporaryDirectory()
         // Construct the test session.
         self.service = try await SWBBuildService(connectionMode: connectionMode, variant: variant)
-        let (result, sessionDiagnostics) = await service.createSession(name: #function, cachePath: tmpDir.path.str)
+        let (result, sessionDiagnostics) = await service.createSession(name: #function, cachePath: tmpDir.path.str, environment: environment)
         self.sessionDiagnostics = sessionDiagnostics
         do {
             self.session = try result.get()
@@ -203,8 +203,8 @@ extension SWBRunDestinationInfo: _RunDestinationInfo {
 
 extension SWBBuildService {
     /// Overload of `createSession` which supplies an inferior products path.
-    package func createSession(name: String, developerPath: String? = nil, cachePath: String?) async -> (Result<SWBBuildServiceSession, any Error>, [SwiftBuildMessage.DiagnosticInfo]) {
-        return await createSession(name: name, developerPath: developerPath, cachePath: cachePath, inferiorProductsPath: Core.inferiorProductsPath()?.str, environment: [:])
+    package func createSession(name: String, developerPath: String? = nil, cachePath: String?, environment: [String:String] = [:]) async -> (Result<SWBBuildServiceSession, any Error>, [SwiftBuildMessage.DiagnosticInfo]) {
+        return await createSession(name: name, developerPath: developerPath, cachePath: cachePath, inferiorProductsPath: Core.inferiorProductsPath()?.str, environment: environment)
     }
 }
 

Tests/SwiftBuildTests/ToolchainTests.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import struct Foundation.UUID
+
+import SwiftBuild
+import SwiftBuildTestSupport
+
+import SWBCore
+import SWBTestSupport
+@_spi(Testing) import SWBUtil
+
+import Testing
+
+@Suite
+fileprivate struct ToolchainTests: CoreBasedTests {
+    @Test(.skipIfEnvironmentVariableSet(key: .externalToolchainsDir))
+    func toolchainLookupByPath() async throws {
+        try await withTemporaryDirectory { (temporaryDirectory: NamedTemporaryDirectory) in
+            let tmpDir = temporaryDirectory.path
+            try await withAsyncDeferrable { deferrable in
+                try localFS.createDirectory(tmpDir.join("toolchain.xctoolchain"))
+                try await localFS.writePlist(tmpDir.join("toolchain.xctoolchain/Info.plist"), .plDict(["Identifier": "com.foo.bar"]))
+                let testSession = try await TestSWBSession(temporaryDirectory: temporaryDirectory, environment: ["EXTERNAL_TOOLCHAINS_DIR": tmpDir.str])
+                await deferrable.addBlock {
+                    await #expect(throws: Never.self) {
+                        try await testSession.close()
+                    }
+                }
+
+                let id = try await testSession.session.lookupToolchain(at: tmpDir.join("toolchain.xctoolchain").str)
+                #expect(id?.rawValue == "com.foo.bar")
+            }
+        }
+    }
+}