Sourcemaps stop working due to multiline comment + CRLF line endings

What version of Next.js are you using?

Happens in at least 12.0.0, 12.0.7, 12.0.8-canary.5 and 12.0.8-canary.8.

What version of Node.js are you using?

16.13.1

What browser are you using?

Chrome

What operating system are you using?

Windows

How are you deploying your application?

next dev

Describe the Bug

When my function has a multiline comment, sourcemaps break. I can’t set a breakpoint on the first console.log and the variables in “Scope” make no sense:

Expected Behavior

I expected the same behavior as when the multiline comment is removed, so being able to set a breakpoint on the first console.log and the “Scope” looking like this:

To Reproduce

• Clone https://github.com/leroydev/nextjs-sourcemaps (it’s a minimal working example, just 1 extra commit on top of npx create-next-app@latest --ts)
• Execute yarn to install the dependencies
• Run yarn dev to start Next.js in development
• Open http://localhost:3000
• Open Chrome DevTools -> CTRL + P -> LogSomeText.ts
• Set breakpoints inside the function and reload

You can see that when you completely remove the multiline comment in LogSomeText.ts, you can set a breakpoint on the first console.log again and the variables in the scope make sense again.

[leroydev]

I think this might possibly be fixed in https://github.com/swc-project/swc/pull/3023, which has been released in swc_ecma_codegen 0.83.2. I can’t get a local Next.js version to work with a custom SWC build though, so I unfortunately can’t verify this.

[balazsorban44]

I am on Linux, and I used your reproduction.

You are correct though, I could reproduce it by changing the line ending to CRLF and resave the LogSomeText.ts file.

It happens when using the SWC transform.