Add support for loading supported features from share/swift/features.json

Sources/SwiftDriver/Driver/Driver.swift

@@ -330,9 +330,15 @@ public struct Driver {
   /// A collection of all the flags the selected toolchain's `swift-frontend` supports
   public let supportedFrontendFlags: Set<String>
 
+  /// A collection of all the features the selected toolchain's `swift-frontend` supports
+  public let supportedFrontendFeatures: Set<String>
+
   /// A global queue for emitting non-interrupted messages into stderr
   public static let stdErrQueue = DispatchQueue(label: "org.swift.driver.emit-to-stderr")
 
+  enum KnownCompilerFeature: String {
+    case emit_abi_descriptor = "emit-abi-descriptor"
+  }
 
   lazy var sdkPath: VirtualPath? = {
     guard let rawSdkPath = frontendTargetInfo.sdkPath?.path else {
@@ -364,6 +370,10 @@ public struct Driver {
     }
   }
 
+  func isFeatureSupported(_ feature: KnownCompilerFeature) -> Bool {
+    return supportedFrontendFeatures.contains(feature.rawValue)
+  }
+
   /// Handler for emitting diagnostics to stderr.
   public static let stderrDiagnosticsHandler: DiagnosticsEngine.DiagnosticsHandler = { diagnostic in
     stdErrQueue.sync {
@@ -606,11 +616,12 @@ public struct Driver {
                                                                                outputFileMap: outputFileMap)
 
     self.supportedFrontendFlags =
-      try Self.computeSupportedCompilerFeatures(of: self.toolchain, hostTriple: self.hostTriple,
+      try Self.computeSupportedCompilerArgs(of: self.toolchain, hostTriple: self.hostTriple,
                                                 parsedOptions: &self.parsedOptions,
                                                 diagnosticsEngine: diagnosticEngine,
                                                 fileSystem: fileSystem, executor: executor,
                                                 env: env)
+    self.supportedFrontendFeatures = try Self.computeSupportedCompilerFeatures(of: self.toolchain, env: env)
 
     self.enabledSanitizers = try Self.parseSanitizerArgValues(
       &parsedOptions,

Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift

@@ -335,7 +335,7 @@ public extension Driver {
       .appending(component: libScanner)
   }
 
-  fileprivate static func getRootPath(of toolchain: Toolchain, env: [String: String])
+  static func getRootPath(of toolchain: Toolchain, env: [String: String])
   throws -> AbsolutePath {
     if let overrideString = env["SWIFT_DRIVER_SWIFT_SCAN_TOOLCHAIN_PATH"] {
       return try AbsolutePath(validating: overrideString)

Sources/SwiftDriver/Jobs/EmitModuleJob.swift

@@ -87,9 +87,13 @@ extension Driver {
       commandLine.appendFlag(.parseAsLibrary)
     }
 
+    let outputPath = VirtualPath.lookup(moduleOutputPath)
     commandLine.appendFlag(.o)
-    commandLine.appendPath(VirtualPath.lookup(moduleOutputPath))
-
+    commandLine.appendPath(outputPath)
+    if isFeatureSupported(.emit_abi_descriptor) {
+      commandLine.appendFlag(.emitAbiDescriptorPath)
+      commandLine.appendPath(outputPath.replacingExtension(with: .jsonABIBaseline))
+    }
     return Job(
       moduleName: moduleOutputInfo.name,
       kind: .emitModule,

Sources/SwiftDriver/Jobs/EmitSupportedFeaturesJob.swift

@@ -12,6 +12,7 @@
 
 import TSCBasic
 import SwiftOptions
+import Foundation
 
 /// Describes information about the compiler's supported arguments and features
 @_spi(Testing) public struct SupportedCompilerFeatures: Codable {
@@ -52,7 +53,7 @@ extension Toolchain {
 }
 
 extension Driver {
-  static func computeSupportedCompilerFeatures(of toolchain: Toolchain, hostTriple: Triple,
+  static func computeSupportedCompilerArgs(of toolchain: Toolchain, hostTriple: Triple,
                                                parsedOptions: inout ParsedOptions,
                                                diagnosticsEngine: DiagnosticsEngine,
                                                fileSystem: FileSystem,
@@ -85,4 +86,24 @@ extension Driver {
       recordedInputModificationDates: [:]).SupportedArguments
     return Set(decodedSupportedFlagList)
   }
+
+  static func computeSupportedCompilerFeatures(of toolchain: Toolchain,
+                                               env: [String: String]) throws -> Set<String> {
+    struct FeatureInfo: Codable {
+      var name: String
+    }
+    struct FeatureList: Codable {
+      var features: [FeatureInfo]
+    }
+    let jsonPath = try getRootPath(of: toolchain, env: env)
+      .appending(component: "share")
+      .appending(component: "swift")
+      .appending(component: "features.json")
+    guard localFileSystem.exists(jsonPath) else {
+      return Set<String>()
+    }
+    let content = try localFileSystem.readFileContents(jsonPath)
+    let result = try JSONDecoder().decode(FeatureList.self, from: Data(content.contents))
+    return Set(result.features.map {$0.name})
+  }
 }

Sources/SwiftDriver/Jobs/MergeModuleJob.swift

@@ -72,9 +72,14 @@ extension Driver {
       try commandLine.appendLast(.disableIncrementalImports, from: &parsedOptions)
     }
 
+    let outputPath = VirtualPath.lookup(moduleOutputInfo.output!.outputPath)
     commandLine.appendFlag(.o)
-    commandLine.appendPath(VirtualPath.lookup(moduleOutputInfo.output!.outputPath))
+    commandLine.appendPath(outputPath)
 
+    if isFeatureSupported(.emit_abi_descriptor) {
+      commandLine.appendFlag(.emitAbiDescriptorPath)
+      commandLine.appendPath(outputPath.replacingExtension(with: .jsonABIBaseline))
+    }
     return Job(
       moduleName: moduleOutputInfo.name,
       kind: .mergeModule,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -5015,6 +5015,12 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testSupportedFeatureJson() throws {
+    let driver = try Driver(args: ["swiftc", "-emit-module", "foo.swift"])
+    XCTAssertFalse(driver.supportedFrontendFeatures.isEmpty)
+    XCTAssertTrue(driver.supportedFrontendFeatures.contains("experimental-skip-all-function-bodies"))
+  }
+
   func testFilelist() throws {
     do {
       var driver = try Driver(args: ["swiftc", "-emit-module", "./a.swift", "./b.swift", "./c.swift", "-module-name", "main", "-target", "x86_64-apple-macosx10.9", "-driver-filelist-threshold=0", "-no-emit-module-separately"])