Introduce build tools plugin to capture static build configuration

Author: sidepelican

Package.swift

@@ -123,7 +123,7 @@ let package = Package(
     .package(url: "https://github.com/apple/swift-system", from: "1.4.0"),
     .package(url: "https://github.com/apple/swift-log", from: "1.2.0"),
     .package(url: "https://github.com/apple/swift-collections", .upToNextMinor(from: "1.3.0")), // primarily for ordered collections
-    .package(url: "https://github.com/swiftlang/swift-subprocess.git", from: "0.2.1", traits: ["SubprocessFoundation"]),
+    .package(url: "https://github.com/swiftlang/swift-subprocess.git", from: "0.4.0", traits: ["SubprocessFoundation"]),
 
     // Benchmarking
     .package(url: "https://github.com/ordo-one/package-benchmark", .upToNextMajor(from: "1.4.0")),
@@ -320,6 +320,7 @@ let package = Package(
       dependencies: [
         .product(name: "SwiftBasicFormat", package: "swift-syntax"),
         .product(name: "SwiftLexicalLookup", package: "swift-syntax"),
+        .product(name: "SwiftIfConfig", package: "swift-syntax"),
         .product(name: "SwiftSyntax", package: "swift-syntax"),
         .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
         .product(name: "ArgumentParser", package: "swift-argument-parser"),
@@ -331,6 +332,25 @@ let package = Package(
       ],
       swiftSettings: [
         .swiftLanguageMode(.v5)
+      ],
+      plugins: [
+        .plugin(name: "_StaticBuildConfigPlugin")
+      ]
+    ),
+
+    .executableTarget(
+      name: "StaticBuildConfigPluginExecutable",
+      dependencies: [
+        .product(name: "Subprocess", package: "swift-subprocess"),
+        .product(name: "SwiftIfConfig", package: "swift-syntax"),
+      ]
+    ),
+
+    .plugin(
+      name: "_StaticBuildConfigPlugin",
+      capability: .buildTool(),
+      dependencies: [
+        "StaticBuildConfigPluginExecutable"
       ]
     ),
 

Plugins/_StaticBuildConfigPlugin/_StaticBuildConfigPlugin.swift

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import PackagePlugin
+
+@main
+struct _StaticBuildConfigPlugin: BuildToolPlugin {
+  func createBuildCommands(context: PluginContext, target: any Target) async throws -> [Command] {
+    let outSwift = context.pluginWorkDirectoryURL.appending(path: "StaticBuildConfiguration+embedded.swift")
+    return [
+      .buildCommand(
+        displayName: "Run -print-static-build-config",
+        executable: try context.tool(named: "StaticBuildConfigPluginExecutable").url,
+        arguments: [outSwift.absoluteURL.path(percentEncoded: false)],
+        environment: [:],
+        inputFiles: [],
+        outputFiles: [outSwift.absoluteURL]
+      )
+    ]
+  }
+}

Sources/JExtractSwiftLib/JExtractDefaultBuildConfiguration.swift

@@ -24,7 +24,11 @@ struct JExtractDefaultBuildConfiguration: BuildConfiguration {
 
   init() {
     let decoder = JSONDecoder()
-    base = try! decoder.decode(StaticBuildConfiguration.self, from: printStaticBuildConfigOutput)
+    do {
+      base = try decoder.decode(StaticBuildConfiguration.self, from: StaticBuildConfiguration.embedded)
+    } catch {
+      fatalError("Embedded StaticBuildConfiguration is broken! data: \(String(data: StaticBuildConfiguration.embedded, encoding: .utf8) ?? "")")
+    }
   }
 
   func isCustomConditionSet(name: String) throws -> Bool {
@@ -93,9 +97,3 @@ extension BuildConfiguration where Self == JExtractDefaultBuildConfiguration {
     .shared
   }
 }
-
-// $ swift frontend -print-static-build-config -target aarch64-unknown-linux-gnu
-private let printStaticBuildConfigOutput = Data(
-  #"{"attributes":["GKInspectable","noDerivative","objcMembers","discardableResult","const","available","usableFromInline","preconcurrency","nonisolated","retroactive","frozen","unsafe","propertyWrapper","lifetime","_extern","inline","abi","storageRestrictions","_opaqueReturnTypeOf","objc","constInitialized","autoclosure","escaping","unchecked","requires_stored_property_inits","convention","attached","nonexhaustive","dynamicCallable","reasync","dynamicMemberLookup","NSCopying","transpose","warn_unqualified_access","c","globalActor","isolated","_local","rethrows","exclusivity","backDeployed","UIApplicationMain","main","nonobjc","resultBuilder","Sendable","_noMetadata","IBDesignable","IBOutlet","export","IBSegueAction","IBAction","derivative","NSApplicationMain","inlinable","concurrent","IBInspectable","NSManaged","_addressable","differentiable"],"compilerVersion":{"components":[6,3]},"customConditions":[],"endianness":"little","features":["BuiltinCreateAsyncTaskWithExecutor","BuiltinCreateAsyncTaskName","Macros","ValueGenericsNameLookup","FreestandingExpressionMacros","AssociatedTypeAvailability","NoncopyableGenerics2","BuiltinInterleave","OptionalIsolatedParameters","BuiltinAddressOfRawLayout","InoutLifetimeDependence","ExtensionMacros","BuiltinBuildMainExecutor","BuiltinStoreRaw","InheritActorContext","IsolatedAny","BuiltinExecutor","LayoutPrespecialization","NonexhaustiveAttribute","InlineAlways","BuiltinCreateTaskGroupWithFlags","ValueGenerics","InlineArrayTypeSugar","BuiltinCreateTask","NonescapableTypes","RetroactiveAttribute","BuiltinTaskRunInline","BuiltinBuildComplexEqualityExecutor","MemorySafetyAttributes","BuiltinBuildExecutor","ModuleSelector","ParameterPacks","MarkerProtocol","ConformanceSuppression","BitwiseCopyable","AddressOfProperty2","UnsafeInheritExecutor","BuiltinCreateAsyncTaskOwnedTaskExecutor","SpecializeAttributeWithAvailability","BuiltinJob","AlwaysInheritActorContext","AsyncExecutionBehaviorAttributes","AsyncSequenceFailure","BorrowingSwitch","PrimaryAssociatedTypes2","NewCxxMethodSafetyHeuristics","ExtensionMacroAttr","BuiltinStackAlloc","TypedThrows","BuiltinContinuation","BuiltinUnprotectedAddressOf","BuiltinSelect","ImplicitSelfCapture","MoveOnlyPartialConsumption","Actors","GeneralizedIsSameMetaTypeBuiltin","MoveOnly","GlobalActors","BuiltinCreateAsyncDiscardingTaskInGroupWithExecutor","NonfrozenEnumExhaustivity","RethrowsProtocol","IsolatedDeinit","BuiltinUnprotectedStackAlloc","BuiltinCreateAsyncTaskInGroupWithExecutor","BuiltinTaskGroupWithArgument","NoAsyncAvailability","ObjCImplementation","AttachedMacros","FreestandingMacros","AsyncAwait","EffectfulProp","BuiltinConcurrencyStackNesting","BuiltinCreateAsyncTaskInGroup","ConcurrentFunctions","BuiltinHopToActor","BuiltinIntLiteralAccessors","BodyMacros","BuiltinVectorsExternC","BuiltinCreateAsyncDiscardingTaskInGroup","RawIdentifiers","NonescapableAccessorOnTrivial","UnavailableFromAsync","IsolatedAny2","LexicalLifetimes","SendableCompletionHandlers","BuiltinAssumeAlignment","AssociatedTypeImplements","Sendable","ABIAttributeSE0479","BuiltinBuildTaskExecutorRef","LifetimeDependenceMutableAccessors","BitwiseCopyable2","IsolatedConformances","ExpressionMacroDefaultArguments","NoncopyableGenerics","SendingArgsAndResults","MoveOnlyResilientTypes","BuiltinEmplaceTypedThrows"],"languageMode":{"components":[5,10]},"targetArchitectures":["arm64"],"targetAtomicBitWidths":[128,64,32,16,8],"targetEnvironments":[],"targetOSs":["Linux"],"targetObjectFileFormats":["ELF"],"targetPointerAuthenticationSchemes":["_none"],"targetPointerBitWidth":64,"targetRuntimes":["_Native","_multithreaded"]}"#
-    .utf8
-)

Sources/StaticBuildConfigPluginExecutable/StaticBuildConfigPluginExecutable.swift

@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Subprocess
+import SwiftIfConfig
+
+@main struct StaticBuildConfigPluginExecutable {
+  static func main() async throws {
+    let args = CommandLine.arguments
+    guard args.count > 1 else {
+      print("Usage: \(args[0]) <destination_path>")
+      return
+    }
+    let dst = URL(fileURLWithPath: args[1])
+
+    let data = try await loadStaticBuildConfig()
+    let template = #"""
+      import Foundation
+      import SwiftIfConfig
+
+      extension StaticBuildConfiguration {
+        static var embedded: Data {
+          Data(#"\#(data)"#.utf8)
+        }
+      }
+      """#
+    try template.write(to: dst, atomically: true, encoding: .utf8)
+  }
+
+  static func loadStaticBuildConfig() async throws -> String {
+    #if compiler(>=6.3)
+    let result = try await run(
+      .name("swift"),
+      arguments: ["frontend", "-print-static-build-config", "-target", "aarch64-unknown-linux-gnu"],
+      output: .string(limit: 65536),
+      error: .string(limit: 65536)
+    )
+    if let error = result.standardError, !error.isEmpty {
+      fatalError(error)
+    }
+    return result.standardOutput ?? ""
+    #else
+    #if compiler(>=6.2)
+    let configuration = StaticBuildConfiguration(
+      languageVersion: .init(components: [5, 10]),
+      compilerVersion: .init(components: [6, 2])
+    )
+    #else
+    let configuration = StaticBuildConfiguration(
+      languageVersion: .init(components: [5, 10]),
+      compilerVersion: .init(components: [6, 1])
+    )
+    #endif
+    let encoder = JSONEncoder()
+    return String(data: try encoder.encode(configuration), encoding: .utf8) ?? ""
+    #endif
+  }
+}