   
   private(set) var sourceSwiftDepsMap = BidirectionalMap<TypedVirtualPath, SwiftDeps>()
 
-  // Supports requests from the driver to getExternalDependencies.
+  // The set of paths to external dependencies discovered during the integration
+  // process.
   public internal(set) var externalDependencies = Set<ExternalDependency>()
-  
+
   let verifyDependencyGraphAfterEveryImport: Bool
   let emitDependencyDotFileAfterEveryImport: Bool
   let reporter: IncrementalCompilationState.Reporter?

    tracedNodes.insert(n)
  }
  func ensureGraphWillRetraceDependents<Nodes: Sequence>(of nodes: Nodes)
  where Nodes.Element == Node
  {
    nodes.forEach { tracedNodes.remove($0) }
  }

    reporter: IncrementalCompilationState.Reporter?,
    fileSystem: FileSystem
  ) -> (ModuleDependencyGraph, inputsWithMalformedSwiftDeps: [(TypedVirtualPath, VirtualPath)])?
    where Inputs.Element == TypedVirtualPath
  {
    let emitOpt = Option.driverEmitFineGrainedDependencyDotFileAfterEveryImport
    let veriOpt = Option.driverVerifyFineGrainedDependencyGraphAfterEveryImport
