[PackageModel] Toolchain: Add a way to retrieve features supported by the Swift compiler

Author: xedin

Sources/PackageModel/CMakeLists.txt

@@ -58,6 +58,7 @@ add_library(PackageModel
   SwiftSDKs/SwiftSDKBundleStore.swift
   Toolchain.swift
   ToolchainConfiguration.swift
+  Toolchain+SupportedFeatures.swift
   Toolset.swift
   ToolsVersion.swift
   ToolsVersionSpecificationGeneration.swift

Sources/PackageModel/Toolchain+SupportedFeatures.swift

@@ -0,0 +1,110 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 Basics
+
+import enum TSCBasic.JSON
+import TSCUtility
+
+public enum SwiftCompilerFeature {
+    case upcoming(name: String, migratable: Bool, enabledIn: SwiftLanguageVersion)
+    case experimental(name: String, migratable: Bool)
+
+    public var upcoming: Bool {
+        switch self {
+        case .upcoming: true
+        case .experimental: false
+        }
+    }
+
+    public var experimental: Bool {
+        switch self {
+        case .upcoming: false
+        case .experimental: true
+        }
+    }
+
+    public var name: String {
+        switch self {
+        case .upcoming(name: let name, migratable: _, enabledIn: _):
+            name
+        case .experimental(name: let name, migratable: _):
+            name
+        }
+    }
+
+    public var migratable: Bool {
+        switch self {
+        case .upcoming(name: _, migratable: let migratable, enabledIn: _):
+            migratable
+        case .experimental(name: _, migratable: let migratable):
+            migratable
+        }
+    }
+}
+
+extension Toolchain {
+    public var swiftCompilerSupportedFeatures: [SwiftCompilerFeature] {
+        get throws {
+            let compilerOutput: String
+            do {
+                let result = try AsyncProcess.popen(args: swiftCompilerPath.pathString, "-print-supported-features")
+                compilerOutput = try result.utf8Output().spm_chomp()
+            } catch {
+                throw InternalError("Failed to get supported features info (\(error.interpolationDescription))")
+            }
+
+            if compilerOutput.isEmpty {
+                return []
+            }
+
+            let parsedSupportedFeatures: JSON
+            do {
+                parsedSupportedFeatures = try JSON(string: compilerOutput)
+            } catch {
+                throw InternalError(
+                    "Failed to parse supported features info (\(error.interpolationDescription)).\nRaw compiler output: \(compilerOutput)"
+                )
+            }
+
+            let features: JSON = try parsedSupportedFeatures.get("features")
+
+            let upcoming: [SwiftCompilerFeature] = try features.getArray("upcoming").map {
+                let name: String = try $0.get("name")
+                let migratable: Bool? = $0.get("migratable")
+                let enabledIn: String = try $0.get("enabled_in")
+
+                guard let mode = SwiftLanguageVersion(string: enabledIn) else {
+                    throw InternalError("Unknown swift language mode: \(enabledIn)")
+                }
+
+                return .upcoming(
+                    name: name,
+                    migratable: migratable ?? false,
+                    enabledIn: mode
+                )
+            }
+
+            let experimental: [SwiftCompilerFeature] = try features.getArray("experimental").map {
+                let name: String = try $0.get("name")
+                let migratable: Bool? = $0.get("migratable")
+
+                return .experimental(
+                    name: name,
+                    migratable: migratable ?? false
+                )
+            }
+
+            return upcoming + experimental
+        }
+    }
+}