minify should not remove licence comments

[tbjgolden]

Describe the bug

Many users will be unaware that they could be breaking their software licence by having minify: true.

Other minifiers seem to use the convention that if a comment:

• starts with a ! (e.g. /*! license ... */ or //! license ...), OR
• looks like it contains a JSDoc licence /** @license */

that it should not be removed with the default minify settings.

Input code

/*! MIT @lorem example.org */

foo();

Config

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false
    },
    "target": "es5",
    "loose": false,
    "minify": {
      "compress": false,
      "mangle": false
    }
  },
  "module": {
    "type": "es6"
  },
  "minify": true,
  "isModule": true
}

Playground link

https://play.swc.rs/?version=1.3.23&code=H4sIAAAAAAAAA9PXUlTISM3JyVcozy%2FKSVHQ0ufiSsvP19C05gIAxeneNhsAAAA%3D&config=H4sIAAAAAAAAA0WMSwrDMAxE76K1t%2B0id8ghhKsEF%2F%2BQFIgxvnvlkpCdZubpdfiKh6VDRRbieUnLiicsQD6heA5VwRlm1YZRaDhQ5J10IvKyLZYidK0OUshha9PkS6pMIs%2BEeY83OUyUyueYRQdtlf7CN4zHoXzYW5D14mYeP5P5%2B3m0AAAA

Expected behavior

Comment is not removed

Actual behavior

Commit is removed

Version

1.3.23

Additional context

No response

[alexander-akait]

Looks like we don't remove them, we just don't print them, try to disable minify

[tbjgolden]

Been doing some research:

The defacto standard has been to not remove comments with an exclamation at the start: /*! ... */, //! ..., or to remove comments containing: @license.

• terser, uglify, support this option behaviour by default
• google closure compiler does not remove these comments
• babel minify supports @license by default, but not !
• esbuild has this option --legal-comments but has it disabled by default
• swc has this option compress.format.comments: "some" but has it disabled by default

Only esbuild and swc do not try to preserve legal comments by default - perhaps it would make sense for both projects to enable it.

evanw/esbuild#2745

[ishowta]

When I specify an empty object for minify in playground "minify": {}, the comment disappears, but when I remove the minify field, the comment appears.

Also, when I run it locally, the license comment is preserved, but the documentation says the default is false.
https://swc.rs/docs/configuration/minification#jscminifyformat

[tbjgolden]

esbuild has now re-enabled their comment preservation, so swc is the only minifier that I'm aware of that has this disabled by default

See for rationale:
evanw/esbuild#2745

[ishowta]

@tbjgolden I was just looking into minifier license preservation too, at least if I don't specify a config file, the license comments are preserved. I confirmed that Nextjs13 (which uses swc internally) also preserve the license comments. please see my above comment.

[swc-bot]

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