[TS] empty import type declaration makes initial test run fail

[m-ronchi]

Summary

if a file contains an import in the form

import type { } from "some module";

then stryker generates an invalid import statement in the mutated ts file:

import type from "some module";

which fails to compile with the error

TSError: ⨯ Unable to compile TypeScript:
src/index.ts(65,13): error TS1005: '=' expected.

Stryker config

{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "_comment": "This config was generated using 'stryker init'. Please take a look at: https://stryker-mutator.io/docs/stryker-js/configuration/ for more information",
  "packageManager": "npm",
  "reporters": [
    "html",
    "clear-text",
    "progress"
  ],
  "testRunner": "mocha",
  "coverageAnalysis": "perTest",
  "checkers": [
    "typescript"
  ],
  "tsconfigFile": "tsconfig.json"
}

Test runner config

mocharc.json

{
    "$schema": "https://json.schemastore.org/mocharc",
    "require": [
        "ts-node/register",
        "source-map-support/register"
    ],
    "spec": [
        "test/**/*.spec.ts"
    ]
}

Stryker environment

├── @stryker-mutator/core@5.6.1
├── @stryker-mutator/mocha-runner@5.6.1
├── @stryker-mutator/typescript-checker@5.6.1

+-- mocha@9.2.0

Test runner environment

mocha

Your Environment

software	version(s)
node	16
npm	8
Operating System	mac

Add stryker.log
stryker.log

code-mutated.zip
code-original.zip

[nicojs]

A small correction

import type { } from 'some-module';

Gets instrumented to:

import type 'some-module';

Which indeed cannot be compiled with tsc.

Will have to investigate further.

[nicojs]

issue3386.zip

[nicojs]

It seems that both code examples have the exact same AST. So I'm not sure if there is anything we can do about it. @m-ronchi what exactly is your use case for import type {} from 'some-module'?

[m-ronchi]

it contains an external module augmentation, plus other code that is injected at an upper layer. I need to import the type declarations when I just include the code (for unit tests, external module is mocked).

more specifically, it is a fastify plugin with

import fp from "fastify-plugin";

declare module "fastify" {
    interface FastifyInstance { // add myPlugin to external type declaration
        myPlugin: Foo;
    }
}

export const plugin = fp(function (fastify) {
    fastify.decorate("myPlugin", foo); // add myPlugin to runtime instance
});

import type declarations are seen by tsc but stripped at runtime, while import "module" is retained for runtime side effects

[nicojs]

I see. No easy solution I'm afraid. I've opened babel/babel#14250

[nicojs]

Some traction there, hopefully a fix soon

[bartekleon]

supposedly fixed in https://github.com/babel/babel/releases/tag/v7.17.7 babel/babel#14309
it seems we are using 7.18 now, so it should be working now. Could you check if issue still persists?

[m-ronchi]

looks like it's fixed