[Bug]: commonjs source-maps sources point to .js and cjs files contain duplicated sourceMappingURL

[Hotell]

Library

React Components / v9 (@fluentui/react-components)

Are you reporting Accessibility issue?

None

Reproduction

Pre swc (using TS):

• esm map: https://unpkg.com/@fluentui/[email protected]/lib/Body1.js.map
• cjs map: https://unpkg.com/@fluentui/[email protected]/lib-commonjs/Body1.js.map
• cjs: https://unpkg.com/@fluentui/[email protected]/lib-commonjs/Body1.js

Post swc:

• esm map: https://unpkg.com/@fluentui/[email protected]/lib/Body1.js.map

• cjs map: https://unpkg.com/@fluentui/[email protected]/lib-commonjs/Body1.js.map

  • duplicate sourceMappingURL present within the source map as well

• cjs: https://unpkg.com/@fluentui/[email protected]/lib-commonjs/Body1.js

  • 

Bug Description

Actual Behavior

After migration to swc, source maps for commonjs inputs don't point to TS original source anymore.

Also the sourceMappingURL is being printed twice within cjs output (which is present within the source map )

Expected Behavior

This regression is actually expected, but we didn't thought about it while implementing the change, as our transpilation pipeline changed

From

graph LR;
 
S["Start"]
E["End"]
B["Babel"]

    S-->TSC:esm-->B
    S-->TSC:cjs-->B
    B-->E;

Loading

To

graph LR;
 
S["Start"]
E["End"]
B["Babel"]

    S-->SWC:esm-->B-->SWC:cjs-->E

Loading

Besides the duplicated sourceMappingURL emit within cjs output, it shouldn't have any real impact for consumers, as we use sourcesContent which is a source of truth for the actual source mapping.

More feedback is needed.

Actionable for now is to reduce that duplicate emit for commonjs.

Logs

No response

Requested priority

Normal

Products/sites affected

No response

Are you willing to submit a PR to fix?

yes

Validations

• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.

Related issues/PRs

#27250

[layershifter]

It's clearly SWC bug: https://codesandbox.io/p/sandbox/funny-wildflower-wnxf1b

$ npx swc ./index.js -o output.esm.js --config module.type=es6 --source-maps=true

⬇️⬇️⬇️

import path from "path";
console.log("Hello CodeSandbox", path.dirname("./foo/bar.js"));


//# sourceMappingURL=output.esm.js.map

$ npx swc ./output.esm.js -o output.cjs.js --config module.type=commonjs --source-maps=true

⬇️⬇️⬇️

"use strict";
Object.defineProperty(exports, "__esModule", {
    value: true
});
var _path = /*#__PURE__*/ _interopRequireDefault(require("path"));
function _interopRequireDefault(obj) {
    return obj && obj.__esModule ? obj : {
        default: obj
    };
}
console.log("Hello CodeSandbox", _path.default.dirname("./foo/bar.js")); //# sourceMappingURL=output.esm.js.map


//# sourceMappingURL=output.cjs.js.map

👆"sourceMappingURL" comment is doubled

[Hotell]

thanks for taking additional look on this @layershifter 🙌.

yeah I'm aware about this. not sure if it's a bug or rather missing feature.

Babel does this like following -> checks for that source map comment, removes it as present, generates new one to provide accurate source map to transformed content. Though some users reported this as bug on babel side.

SWC doesn't do what babel does, which might be missing feature ?

anyways lets report this to swc folks. ty

[microsoft-github-policy-service]

Because this issue has not had activity for over 180 days, we're automatically closing it for house-keeping purposes.

Still require assistance? Please, create a new issue with up-to date details.

[microsoft-github-policy-service]

Because this issue has not had activity for over 180 days, we're automatically closing it for house-keeping purposes.

Still require assistance? Please, create a new issue with up-to date details.