@swc/core@1.3.51 does not return sourcemap for type-only files, causes error in updateSourceMap

[erikthiem-immuta]

Search Terms

SWC

Expected Behavior

I am using ts-node with the --swc flag. I expect it to work. It works fine for me on SWC < 1.3.50

Actual Behavior

I tried upgrading to SWC >= 1.3.50 today and it caused ts-node to not work. I unfortunately did not see much useful output. If there is a way to get more useful output to fix this, I am happy to try it.

Steps to reproduce the problem

Upgrade to SWC >= 1.3.50

Minimal reproduction

Be on ts-node version 10.9.1 and SWC version 1.3.50 and try to use ts-node with the --swc flag.

Specifications

• ts-node version: 10.9.1
• node version: 18.x
• TypeScript version: 4.8.4
• tsconfig.json, if you're using one:

"ts-node": {
    "swc": true
}

• package.json:
  The relevant part would be:

`... node_modules/ts-node/dist/bin.js --swc --transpile-only index.ts`

• Operating system and version: Mac
• If Windows, are you using WSL or WSL2?:

[koh110]

I have same issue.
After changing the version of @swc/core@1.3.51, I encountered an error in --swc mode.
The cause of the error seems to be import a file that only exports types.

Since a file that only exports types does not generate a SourceMap file when using @swc/core@1.3.51.
So it seems that updateSourceMap throw error because undefined is given to JSON.parse.
ref

I have confirmed that the error does not occur when passing {} instead of undefined.

function updateSourceMap(sourceMapText: string, fileName: string) {
  const sourceMap = JSON.parse(sourceMapText ?? {});

I want to send PR, but I still can't think of how to write tests.