[SwiftSyntax] Add #_objectFileFormat compilation conditional

Sources/SwiftIfConfig/BuildConfiguration.swift

@@ -37,6 +37,17 @@ public enum CanImportVersion {
   case underlyingVersion(VersionTuple)
 }
 
+enum BuildConfigurationError: Error, CustomStringConvertible {
+  case experimentalFeature(name: String)
+
+  var description: String {
+    switch self {
+    case .experimentalFeature(let name):
+      return "'name' is an experimental feature"
+    }
+  }
+}
+
 /// Captures information about the build configuration that can be
 /// queried in a `#if` expression, including OS, compiler version,
 /// enabled language features, and available modules.
@@ -214,6 +225,22 @@ public protocol BuildConfiguration {
   /// pointer authentication scheme.
   func isActiveTargetPointerAuthentication(name: String) throws -> Bool
 
+  /// Determine whether the given name is the active target object file format (e.g., ELF).
+  ///
+  /// The target object file format can only be queried by an experimental
+  /// syntax `_objectFileFormat(<name>)`, e.g.,
+  ///
+  /// ```swift
+  /// #if _objectFileFormat(ELF)
+  /// // Special logic for ELF object file formats
+  /// #endif
+  /// ```
+  /// - Parameters:
+  ///   - name: The name of the object file format.
+  /// - Returns: Whether the target object file format matches the given name.
+  @_spi(ExperimentalLanguageFeatures)
+  func isActiveTargetObjectFileFormat(name: String) throws -> Bool
+
   /// The bit width of a data pointer for the target architecture.
   ///
   /// The target's pointer bit width (which also corresponds to the number of
@@ -276,3 +303,13 @@ public protocol BuildConfiguration {
   /// #endif
   var compilerVersion: VersionTuple { get }
 }
+
+/// Default implementation of BuildConfiguration, to avoid a revlock with the
+/// swift repo, and breaking clients with the new addition to the protocol.
+extension BuildConfiguration {
+  /// FIXME: This should be @_spi(ExperimentalLanguageFeatures) but cannot due
+  /// to rdar://147943518, https://github.com/swiftlang/swift/issues/80313
+  public func isActiveTargetObjectFileFormat(name: String) throws -> Bool {
+    throw BuildConfigurationError.experimentalFeature(name: "_objectFileFormat")
+  }
+}

Sources/SwiftIfConfig/IfConfigDiagnostic.swift

@@ -159,7 +159,8 @@ extension IfConfigDiagnostic: DiagnosticMessage {
   var severity: SwiftDiagnostics.DiagnosticSeverity {
     switch self {
     case .compilerVersionSecondComponentNotWildcard, .ignoredTrailingComponents,
-      .likelySimulatorPlatform, .likelyTargetOS, .endiannessDoesNotMatch, .macabiIsMacCatalyst:
+      .likelySimulatorPlatform, .likelyTargetOS, .endiannessDoesNotMatch,
+      .macabiIsMacCatalyst:
       return .warning
     default: return .error
     }

Sources/SwiftIfConfig/IfConfigEvaluation.swift

@@ -307,6 +307,9 @@ func evaluateIfConfig(
     case .targetEnvironment:
       return doSingleIdentifierArgumentCheck(configuration.isActiveTargetEnvironment, role: "environment")
 
+    case ._objectFileFormat:
+      return doSingleIdentifierArgumentCheck(configuration.isActiveTargetObjectFileFormat, role: "object file format")
+
     case ._runtime:
       return doSingleIdentifierArgumentCheck(configuration.isActiveTargetRuntime, role: "runtime")
 
@@ -818,6 +821,10 @@ private struct CanImportSuppressingBuildConfiguration<Other: BuildConfiguration>
     return try other.isActiveTargetPointerAuthentication(name: name)
   }
 
+  func isActiveTargetObjectFileFormat(name: String) throws -> Bool {
+    return try other.isActiveTargetObjectFileFormat(name: name)
+  }
+
   var targetPointerBitWidth: Int { return other.targetPointerBitWidth }
 
   var targetAtomicBitWidths: [Int] { return other.targetAtomicBitWidths }

Sources/SwiftIfConfig/IfConfigFunctions.swift

@@ -49,6 +49,9 @@ enum IfConfigFunctions: String {
   /// A check for the target bit width of a pointer (e.g., _64)
   case _pointerBitWidth
 
+  /// A check for the target object file format (e.g., ELF)
+  case _objectFileFormat
+
   /// A check for the target runtime paired with the Swift runtime (e.g., _ObjC)
   /// via `_runtime(<name>)`.
   case _runtime
@@ -69,7 +72,7 @@ enum IfConfigFunctions: String {
       return true
 
     case .hasAttribute, .hasFeature, .canImport, .os, .arch, .targetEnvironment,
-      ._hasAtomicBitWidth, ._endian, ._pointerBitWidth, ._runtime, ._ptrauth, .defined:
+      ._hasAtomicBitWidth, ._endian, ._pointerBitWidth, ._objectFileFormat, ._runtime, ._ptrauth, .defined:
       return false
     }
   }

Tests/SwiftIfConfigTest/EvaluateTests.swift

@@ -208,6 +208,8 @@ public class EvaluateTests: XCTestCase {
     assertIfConfig("_pointerBitWidth(_32)", .inactive)
     assertIfConfig("_hasAtomicBitWidth(_64)", .active)
     assertIfConfig("_hasAtomicBitWidth(_128)", .inactive)
+    assertIfConfig("_objectFileFormat(ELF)", .active)
+    assertIfConfig("_objectFileFormat(MachO)", .inactive)
 
     assertIfConfig(
       "_endian(mid)",

Tests/SwiftIfConfigTest/TestingBuildConfiguration.swift

@@ -99,6 +99,10 @@ struct TestingBuildConfiguration: BuildConfiguration {
     name == "arm64e"
   }
 
+  func isActiveTargetObjectFileFormat(name: String) throws -> Bool {
+    name == "ELF"
+  }
+
   var targetPointerBitWidth: Int { 64 }
 
   var targetAtomicBitWidths: [Int] { [32, 64] }