jextract: Evaluate IfConfigDecl and add --static-build-config option (#671)

Co-authored-by: Konrad `ktoso` Malawski <konrad.malawski@project13.pl>

Author: sidepelican

Package.swift

@@ -118,12 +118,12 @@ let package = Package(
   ],
   dependencies: [
     swiftJavaJNICoreDep,
-    .package(url: "https://github.com/swiftlang/swift-syntax", from: "602.0.0"),
+    .package(url: "https://github.com/swiftlang/swift-syntax", from: "603.0.0"),
     .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
     .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/JExtractSwiftPlugin/JExtractSwiftPlugin.swift

@@ -46,7 +46,7 @@ struct JExtractSwiftBuildToolPlugin: SwiftJavaPluginProtocol, BuildToolPlugin {
     // The name of the configuration file SwiftJava.config from the target for
     // which we are generating Swift wrappers for Java classes.
     let configFile = sourceDir.appending(path: "swift-java.config")
-    let configuration = try readConfiguration(sourceDir: sourceDir)
+    let configuration = try readConfiguration(configPath: configFile)
 
     // We use the the usual maven-style structure of "src/[generated|main|test]/java/..."
     // that is common in JVM ecosystem
@@ -71,6 +71,13 @@ struct JExtractSwiftBuildToolPlugin: SwiftJavaPluginProtocol, BuildToolPlugin {
       //       We'll have to make up some caching inside the tool so we don't re-parse files which have not changed etc.
     ]
 
+    if let staticBuildConfig = configuration?.staticBuildConfigurationFile {
+      guard let resolvedURL = URL(string: staticBuildConfig, relativeTo: configFile) else {
+        fatalError("Could not resolve 'staticBuildConfigurationFile' url: \(staticBuildConfig)")
+      }
+      arguments += ["--static-build-config", resolvedURL.absoluteURL.path(percentEncoded: false)]
+    }
+
     let dependentConfigFilesArguments = dependentConfigFiles.flatMap { moduleAndConfigFile in
       let (moduleName, configFile) = moduleAndConfigFile
       return [

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/Convenience/SwiftSyntax+Extensions.swift

@@ -229,8 +229,10 @@ extension DeclSyntaxProtocol {
       } else {
         "var"
       }
+    case .unexpectedCodeDecl(let node):
+      node.trimmedDescription
     case .usingDecl(let node):
-      node.nameForDebug
+      node.trimmedDescription
     }
   }
 

Sources/JExtractSwiftLib/JExtractDefaultBuildConfiguration.swift

@@ -0,0 +1,99 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 SwiftIfConfig
+import SwiftSyntax
+
+/// A default, fixed build configuration during static analysis for interface extraction.
+struct JExtractDefaultBuildConfiguration: BuildConfiguration {
+  static let shared = JExtractDefaultBuildConfiguration()
+
+  private var base: StaticBuildConfiguration
+
+  init() {
+    let decoder = JSONDecoder()
+    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 {
+    base.isCustomConditionSet(name: name)
+  }
+
+  func hasFeature(name: String) throws -> Bool {
+    base.hasFeature(name: name)
+  }
+
+  func hasAttribute(name: String) throws -> Bool {
+    base.hasAttribute(name: name)
+  }
+
+  func canImport(importPath: [(TokenSyntax, String)], version: CanImportVersion) throws -> Bool {
+    try base.canImport(importPath: importPath, version: version)
+  }
+
+  func isActiveTargetOS(name: String) throws -> Bool {
+    true
+  }
+
+  func isActiveTargetArchitecture(name: String) throws -> Bool {
+    true
+  }
+
+  func isActiveTargetEnvironment(name: String) throws -> Bool {
+    true
+  }
+
+  func isActiveTargetRuntime(name: String) throws -> Bool {
+    true
+  }
+
+  func isActiveTargetPointerAuthentication(name: String) throws -> Bool {
+    true
+  }
+
+  func isActiveTargetObjectFormat(name: String) throws -> Bool {
+    true
+  }
+
+  var targetPointerBitWidth: Int {
+    base.targetPointerBitWidth
+  }
+
+  var targetAtomicBitWidths: [Int] {
+    base.targetAtomicBitWidths
+  }
+
+  var endianness: Endianness {
+    base.endianness
+  }
+
+  var languageVersion: VersionTuple {
+    base.languageVersion
+  }
+
+  var compilerVersion: VersionTuple {
+    base.compilerVersion
+  }
+}
+
+extension BuildConfiguration where Self == JExtractDefaultBuildConfiguration {
+  static var jextractDefault: JExtractDefaultBuildConfiguration {
+    .shared
+  }
+}

Sources/JExtractSwiftLib/Swift2Java.swift

@@ -34,7 +34,6 @@ public struct SwiftToJava {
     }
 
     let translator = Swift2JavaTranslator(config: config)
-    translator.log.logLevel = config.logLevel ?? .info
     let log = translator.log
 
     if config.javaPackage == nil || config.javaPackage!.isEmpty {

Sources/JExtractSwiftLib/Swift2JavaTranslator.swift

@@ -14,6 +14,7 @@
 
 import Foundation
 import SwiftBasicFormat
+import SwiftIfConfig
 import SwiftJavaConfigurationShared
 import SwiftJavaJNICore
 import SwiftParser
@@ -27,6 +28,9 @@ public final class Swift2JavaTranslator {
 
   let config: Configuration
 
+  /// The build configuration used to resolve #if conditional compilation blocks.
+  let buildConfig: any BuildConfiguration
+
   /// The name of the Swift module being translated.
   let swiftModuleName: String
 
@@ -70,6 +74,19 @@ public final class Swift2JavaTranslator {
     self.log = Logger(label: "translator", logLevel: config.logLevel ?? .info)
     self.config = config
     self.swiftModuleName = swiftModule
+
+    if let staticBuildConfigPath = config.staticBuildConfigurationFile {
+      do {
+        let data = try Data(contentsOf: URL(fileURLWithPath: staticBuildConfigPath))
+        let decoder = JSONDecoder()
+        self.buildConfig = try decoder.decode(StaticBuildConfiguration.self, from: data)
+        self.log.info("Using custom static build configuration from: \(staticBuildConfigPath)")
+      } catch {
+        fatalError("Failed to load static build configuration from '\(staticBuildConfigPath)': \(error)")
+      }
+    } else {
+      self.buildConfig = .jextractDefault
+    }
   }
 }
 
@@ -152,6 +169,7 @@ extension Swift2JavaTranslator {
       moduleName: self.swiftModuleName,
       inputs + [dependenciesSource],
       config: self.config,
+      buildConfig: self.buildConfig,
       log: self.log,
     )
     self.lookupContext = SwiftTypeLookupContext(symbolTable: symbolTable)

Sources/JExtractSwiftLib/Swift2JavaVisitor.swift

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import SwiftIfConfig
 import SwiftJavaConfigurationShared
 import SwiftParser
 import SwiftSyntax
@@ -70,7 +71,8 @@ final class Swift2JavaVisitor {
       self.visit(subscriptDecl: node, in: parent)
     case .enumCaseDecl(let node):
       self.visit(enumCaseDecl: node, in: parent)
-
+    case .ifConfigDecl(let node):
+      self.visit(ifConfigDecl: node, in: parent, sourceFilePath: sourceFilePath)
     default:
       break
     }
@@ -366,6 +368,30 @@ final class Swift2JavaVisitor {
     }
   }
 
+  private func visit(
+    ifConfigDecl node: IfConfigDeclSyntax,
+    in parent: ImportedNominalType?,
+    sourceFilePath: String
+  ) {
+    let (clause, _) = node.activeClause(in: translator.buildConfig)
+    if let clause, let elements = clause.elements {
+      switch elements {
+      case .statements(let codeBlock):
+        for codeItem in codeBlock {
+          if let declNode = codeItem.item.as(DeclSyntax.self) {
+            self.visit(decl: declNode, in: parent, sourceFilePath: sourceFilePath)
+          }
+        }
+      case .decls(let memberBlock):
+        for memberItem in memberBlock {
+          self.visit(decl: memberItem.decl, in: parent, sourceFilePath: sourceFilePath)
+        }
+      default:
+        break
+      }
+    }
+  }
+
   private func importAccessor(
     from node: DeclSyntax,
     in typeContext: ImportedNominalType?,