typesrcript_non_null_assertion_transform.js

/**
 * The transformer signature is based on https://github.com/cevek/ttypescript#program
 * Need to use https://github.com/microsoft/TypeScript/blob/bae0f508184280c59d2865a35efc63be362eacfa/src/compiler/factory/nodeFactory.ts
 * The goal is to conver `a!.m()` to `if (!a) { throw new Error('Attempted to use nullish value "a"'} else { a.m() }`
 * https://astexplorer.net/#/gist/9ec2af3e8c15fd2cde848941e14f566b/d9ddca954379374f98a4097d9bde4c346dac8567
 */
export default function (program) {
  const checker = program.getTypeChecker()
  return (context) => {
    return (sourceFile) => {
      const visitor = (node) => {
        if (ts.isNonNullExpression(node)) {
          console.log(node.expression)
          const thrower = context.factory.createThrowStatement(
            context.factory.createNewExpression(
              context.factory.createStringLiteral('Error'),
              undefined,
              ['Use of non null variable']
            )
          )
          return context.factory.createIfStatement(
            context.factory.createPrefixUnaryExpression(
              ts.SyntaxKind.ExclamationToken,
              context.factory.createIdentifier(node.expression.escapedText)
            ),
            thrower
          )
        }

        return ts.visitEachChild(node, visitor, context)
      }
      return ts.visitNode(sourceFile, visitor)
    }
  }
}