TypeScript custom transformers with ts.createSolutionBuilderWithWatch

build.js

var ts = require('typescript');
var diagReport = ts.createBuilderStatusReporter(ts.sys, ts.sys.writeOutputIsTTY && ts.sys.writeOutputIsTTY());

var host = ts.createWatchCompilerHost(
  [__filename],
  { allowJs: true, checkJs: true, outFile: __filename + '.out.js' },
  ts.sys,
  createAndPatchProgram,
  void 0,
  reportWatch);

var buildStart = Date.now();

ts.createWatchProgram(host);

function reportWatch(diag, newLine, options, errorCount) {
  ts.sys.write(typeof errorCount === 'number' ?
    '\x1b[90m ' + (((Date.now() - buildStart) / 1000) + 's        ').slice(0, 10) + '\x1b[0m' :
    'WATCH DIAG ');
  diagReport(diag);

  if (typeof errorCount !== 'number') buildStart = Date.now();
}

var prog;
function createAndPatchProgram() {
  prog = ts.createEmitAndSemanticDiagnosticsBuilderProgram.apply(ts, arguments);
  prog.__oldEmit = prog.emit;
  prog.emit = overrideEmit;
  return prog;
}

function overrideEmit(targetSourceFile, writeFile, cancellationToken, emitOnlyDtsFiles, customTransformers) {
  return this.__oldEmit(
    targetSourceFile,
    writeFile,
    cancellationToken,
    emitOnlyDtsFiles,
    { after: [transformInjectStatementNumbers] }
  );
}

var checker;
/** @param {import('typescript').TransformationContext} context */
function transformInjectStatementNumbers(context) {
  checker = prog.getProgram().getTypeChecker();
  return transformFile;

  function transformFile(sourceFile) {
    return ts.updateSourceFileNode(
      sourceFile,
      sourceFile.statements.map(decorateStatementWithComplexityAndType));
  }
}

function decorateStatementWithComplexityAndType(statement) {
  var nodeCount = 0;
  var type;
  ts.forEachChild(statement, visitStatementChild);

  return ts.addSyntheticLeadingComment(
    statement, ts.SyntaxKind.SingleLineCommentTrivia,
    ' complexity: ' + nodeCount +
    (!type ? '' : ' = ' + checker.typeToString(type)));

  function visitStatementChild(child) {
    nodeCount++;
    if (!type) type = checker.getTypeAtLocation(child);
    if (type.getFlags() === ts.TypeFlags.Any) type = null;
    ts.forEachChild(child, visitStatementChild);
  }
}