Emitted AST should optionally include comments

[saibotsivad]

Describe the feature

When using the parse method in the JavaScript lib @swc/core to generate AST, comments are not emitted. For example:

const swc = require('@swc/core')
const source = `
/**
 * Hello world!
 */
export class Test {}
`
swc.parse(source, {
    syntax: 'typescript',
    comments: true,
    isModule: true,
}).then(out => {
    console.log(JSON.stringify(out.body, undefined, 4))
})

Currently logs this, which notably does not contain the comment:

[ {
    "type": "ExportDeclaration",
    "span": { "start": 25, "end": 45, "ctxt": 0 },
    "declaration": {
        "type": "ClassDeclaration",
        "identifier": {
            "type": "Identifier",
            "span": { "start": 38, "end": 42, "ctxt": 0 },
            "value": "Test",
            "optional": false
        },
        "declare": false,
        "span": { "start": 32, "end": 45, "ctxt": 0 },
        "decorators": [],
        "body": [],
        "superClass": null,
        "isAbstract": false,
        "typeParams": null,
        "superTypeParams": null,
        "implements": []
    }
} ]

Of course, storing comments in the AST increases the size significantly, so it makes sense for this to be optional.

Having the comments in the AST is important to enable certain developer tools, so I would like to have it as an option.

Babel plugin or link to the feature description

No response

Additional context

No response

[kwonoj]

@kdy1 this sounds like similar (not exactly same) discussion we had for plugin transform side comment support.

• Do you think it makes sense if we could have consolidated way to support both?
• if so, any suggestions?

[kdy1]

We can return a map in comments field for parse().
I don't think this is related to transform apis.

[RoenLie]

Any updates on this?

[kwonoj]

If you see the issue does not have an update, that's reflecting the current state. Core team has small resources and sometimes cannot keep up all the feature improvement request from the community vs. internal priorities we are currently focusing.

[RoenLie]

No worries! I just asked since I didn't find it in the milestone it was added to.
You're all doing a great job and it's highly appreciated!

[recover758126]

so, this be solved?

[Nickersoft]

@kdy1 Was this ever implemented?

[Nickersoft]

@kdy1 I actually realized that the TypeScript compiler doesn't preserve comments in its AST either. I was looking at the advanced demo for the TSDoc API and realized they use the TS method getLeadingCommentRanges along with node.pos to find the beginning of declarations and traverse upwards to find the block comment.

I was hoping to do the same using @swc/core instead of the TS compiler, but found this bug in which the span start increases with every invocation of the parser, making it impossible to get an accurate pos position for declarations.

Does this mean there's absolutely no way to extract comments from a file?

[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.