Splitting this off as a new issue so it can be tracked more easily. See the original issue for more context:

output.sourcemapIgnoreList was added to rollup in 3.16.0 (2023-02-17):

• https://github.com/rollup/rollup/blob/master/CHANGELOG.md#3160

  • Support output.sourcemapIgnoreList option to mark file sources as ignored in the x_google_ignoreList attribute of the resulting sourcemap (Introduce sourcemapIgnoreList config predicate rollup/rollup#4848)

microbundle is using a super outdated version of rollup (2.35.1) from 2020-12-14:

• microbundle/package.json

  Line 102 in c76c41f

  "rollup": "^2.35.1",

So before we can implement this change, we'll need to upgrade to a modern version of rollup.

Originally posted by @0xdevalias in #1066 (comment)

microbundle is currently using rollup 2.35.1 (2020-12-14):

• https://github.com/rollup/rollup/blob/master/CHANGELOG.md#2351

output.sourcemapIgnoreList (required to implement #1066) support was added in 3.16.0 (2023-02-17):

• https://github.com/rollup/rollup/blob/master/CHANGELOG.md#3160

Latest version (at time of writing) is 4.6.1 (2023-11-30):

• https://github.com/rollup/rollup/blob/master/CHANGELOG.md#461