inputSourceMap option has a bug

[lewisl9029]

Describe the bug

In types.ts, I see the following docs and type defs for inputSourceMap:

  /**
   * `true` will attempt to load an input sourcemap from the file itself, if it
   * contains a //# sourceMappingURL=... comment. If no map is found, or the
   * map fails to load and parse, it will be silently discarded.
   *
   *  If an object is provided, it will be treated as the source map object itself.
   *
   * Defaults to `true`.
   */
  inputSourceMap?: boolean | string;

The description says that we should be able to pass in the sourcemap as an object, but the types only specify boolean and string, and when I actually try to pass in an object, I get the following error:

Error: Failed to deserialize buffer as swc::config::Options
JSON: {"inputSourceMap":{"version":3,"names":["test"],"sources":["unknown"],"sourcesContent":["export const test = \"1234\""],"mappings":"AAAA,OAAO,MAAMA,IAAI,GAAG,MAAb"}}

Caused by:
    data did not match any variant of untagged enum InputSourceMap at line 1 column 165
    at Compiler.transformSync (/home/runner/O9ukU1Lkv00/node_modules/@swc/core/index.js:137:25)
    at Object.transformSync (/home/runner/O9ukU1Lkv00/node_modules/@swc/core/index.js:217:21)
    at Object.<anonymous> (/home/runner/O9ukU1Lkv00/index.js:10:21)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)

Couldn't see a way to repro this in the playground, so I made a quick repro at replit instead, let me know if there's a preferred alternative: https://replit.com/@lewisl9029/swc-inputSourceMap-repro

Curious if this is a bug or was it never supported in the first place? If it's the latter, please consider this a feature request! I have a use case where I'm using swc as a fast minifier for a babel transformed file (I have a lot of custom babel plugins that still need to be rewritten using the new WASM plugin system before I can replace babel completely), and would like to preserve source mapping functionality if possible. Thanks!

Input code

const swc_ = require('@swc/core')
const babel_ = require('@babel/core')

const {code, map} = 
  babel_.transformSync('export const test = "1234"', { 
    sourceMaps: true 
  })
console.log({ code, map})

const result = swc_.transformSync(code, { inputSourceMap: map })
console.log(result)

Config

No response

Playground link

https://replit.com/@lewisl9029/swc-inputSourceMap-repro

Expected behavior

SWC uses supplied sourcemap object

Actual behavior

SWC crashes with the following output:

{
  code: 'export const test = "1234";',
  map: {
    version: 3,
    file: undefined,
    names: [ 'test' ],
    sourceRoot: undefined,
    sources: [ 'unknown' ],
    sourcesContent: [ 'export const test = "1234"' ],
    mappings: 'AAAA,OAAO,MAAMA,IAAI,GAAG,MAAb'
  }
}
Error: Failed to deserialize buffer as swc::config::Options
JSON: {"inputSourceMap":{"version":3,"names":["test"],"sources":["unknown"],"sourcesContent":["export const test = \"1234\""],"mappings":"AAAA,OAAO,MAAMA,IAAI,GAAG,MAAb"}}

Caused by:
    data did not match any variant of untagged enum InputSourceMap at line 1 column 165
    at Compiler.transformSync (/home/runner/O9ukU1Lkv00/node_modules/@swc/core/index.js:137:25)
    at Object.transformSync (/home/runner/O9ukU1Lkv00/node_modules/@swc/core/index.js:217:21)
    at Object.<anonymous> (/home/runner/O9ukU1Lkv00/index.js:10:21)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)

Version

1.2.179

Additional context

No response

[kdy1]

This is because I copied the description from babel.
This is not a bug

[lewisl9029]

Ah understood. Is there some other way to pass through a sourcemap that only exists in-memory?

[kdy1]

You can stringify it

[lewisl9029]

Ah nice! I just gave that a try, and it no longer throws, but the source locations seem to be off.

I updated the replit with the simplest repro I could think of: https://replit.com/@lewisl9029/swc-inputSourceMap-repro

npm run test2 will run the script from babel before minification, and npm run test will run the script after minified by swc.

test2's stacktrace points to the original source location where the error is thrown, but test's stacktrace seems to be pointing at a completely unrelated location towards the end of the script.

[lewisl9029]

Extracting all the necessary info here for convenience:

This is index.js, the module used to generate the test files:

const swc_ = require('@swc/core')
const babel_ = require('@babel/core')
const fs_ = require('fs')

const { code, map } =
  babel_.transformSync(fs_.readFileSync('./input.js'), {
    sourceMaps: true
  })
console.log({ code, map })

const result = swc_.transformSync(code, {
  inputSourceMap: JSON.stringify(map), 
  sourceMaps: 'inline',
  jsc: {
    minify: {
      compress: true,
      mangle: true,
    },
  },
  minify: true,
})

fs_.writeFileSync('./test.js', result.code)


const result2 =
  babel_.transformSync(fs_.readFileSync('./input.js'), {
    sourceMaps: 'inline'
  })

fs_.writeFileSync('./test2.js', result2.code)

This is input.js, the file used as input to babel:

const test = "1234"

/* this should throw on line 3 */ throw new Error('hi')

const test2 = 1

This is test.js, the output of babel then minified by swc:

throw new Error("hi")
//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInVua25vd24iLCI8YW5vbj4iXSwic291cmNlc0NvbnRlbnQiOlsiY29uc3QgdGVzdCA9IFwiMTIzNFwiXG5cbi8qIHRoaXMgc2hvdWxkIHRocm93IG9uIGxpbmUgMyAqLyB0aHJvdyBuZXcgRXJyb3IoJ2hpJylcblxuY29uc3QgdGVzdDIgPSAxIiwiY29uc3QgdGVzdCA9IFwiMTIzNFwiO1xuLyogdGhpcyBzaG91bGQgdGhyb3cgb24gbGluZSAzICovXG5cbnRocm93IG5ldyBFcnJvcignaGknKTtcbmNvbnN0IHRlc3QyID0gMTsiXSwibmFtZXMiOlsiRXJyb3IiXSwibWFwcGluZ3MiOiJBQUlBLE1BQU0sSUFBQUEsS0FBTixDQUFBLElBQUEsQ0FBQSJ9

This is test2.js, output of just babel:

const test = "1234";
/* this should throw on line 3 */

throw new Error('hi');
const test2 = 1;
//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJuYW1lcyI6WyJ0ZXN0IiwiRXJyb3IiLCJ0ZXN0MiJdLCJzb3VyY2VzIjpbInVua25vd24iXSwic291cmNlc0NvbnRlbnQiOlsiY29uc3QgdGVzdCA9IFwiMTIzNFwiXG5cbi8qIHRoaXMgc2hvdWxkIHRocm93IG9uIGxpbmUgMyAqLyB0aHJvdyBuZXcgRXJyb3IoJ2hpJylcblxuY29uc3QgdGVzdDIgPSAxIl0sIm1hcHBpbmdzIjoiQUFBQSxNQUFNQSxJQUFJLEdBQUcsTUFBYjtBQUVBOztBQUFrQyxNQUFNLElBQUlDLEtBQUosQ0FBVSxJQUFWLENBQU47QUFFbEMsTUFBTUMsS0FBSyxHQUFHLENBQWQifQ==

Results of running test vs test2:

~/swc-inputSourceMap-repro$ npm run test

> swc-inputsourcemap-repro@1.0.0 test
> node --enable-source-maps test.js

Error: hi
    at Object.<anonymous> (/home/runner/swc-inputSourceMap-repro/unknown:5:7)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1157:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47
~/swc-inputSourceMap-repro$ npm run test2

> swc-inputsourcemap-repro@1.0.0 test2
> node --enable-source-maps test2.js

Error: hi
    at Object.<anonymous> (/home/runner/swc-inputSourceMap-repro/unknown:3:41)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1157:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47

[ChrisCindy]

Is this bug fixed ?

[elado]

@ChrisCindy - doesn't seem like, I am still experiencing it. Needed to do some work to drop Babel and use only SWC to have source maps correct.

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.