function createWatchHost(
  ts: typeof import('typescript'),
  context: PluginContext,
  {
    formatHost,
    parsedOptions,
    writeFile,
    status,
    resolveModule,
    transformers
  }: CreateProgramOptions
): WatchCompilerHostOfFilesAndCompilerOptions<BuilderProgram> {
  const createProgram = ts.createEmitAndSemanticDiagnosticsBuilderProgram;
  const diagnostics = buildDiagnosticReporter( ts, context, formatHost );

  //TODO this may also use createSolutionBuilderWithWatchHost to allow file watching.
  const hostBuilder = ts.createSolutionBuilderHost(
    ts.sys,
    createProgram,
    diagnostics
    //TODO implement reportSolutionBuilderStatus, reportWatchStatus
  );

  // Create a instance of the builder to be used to generate file changes.
  // TODO this may also use createSolutionBuilderWithWatch to watch files.
  const builder = ts.createSolutionBuilder( hostBuilder, parsedOptions.projectReferences!.map( ref => ref.path ), {verbose: true} )
  // ts.createSolutionBuilderWithWatch( solutionBuilderHost, )
  builder.build();
  //TODO check timestamps if applicable.

  const baseHost = ts.createWatchCompilerHost(
    parsedOptions.fileNames,
    parsedOptions.options,
    ts.sys,
    createProgram,
    diagnostics,
    status,
    parsedOptions.projectReferences
  );