Document more ways to read package.json in ESM

[berniegp]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

What appears to me like the simplest options to read package.json from an ESM configuration file are not presented in the documentation. This PR adds them.

Special thanks to this SO answer: https://stackoverflow.com/a/66726426/1030527

[berniegp]

I'm debating which version for the 1st example works best for the docs:

    // rollup.config.mjs
    import { readFileSync } from 'fs';
    
    const packageJson = JSON.parse(readFileSync('./package.json'));

or

    // rollup.config.mjs
    import { readFileSync } from 'fs';
    
    const packageJson = JSON.parse(readFileSync(new URL('./package.json', import.meta.url)));

The second option uses this and can prevent mistakes from users copy-pasting the code. It's also slightly more involved...

[lukastaegert]

Thanks a lot! I would be willing to merge this PR as it is for Rollup 2. However, incidentally I just reworked (rather: replaced) the entire section in another PR for Rollup 3: https://github.com/rollup/rollup/pull/4123/files#diff-3bcf69b015e1d47b66389aaafaf606be97b72f19240a58f5d87031b87ae2013cL269-R324

The reason is that I want "untranspiled files" to be the default anyway. They two ways I recommend there are import assertions for Node 18 or createRequire (and we will not support any Node version older than 14). It would be nice if you could have a look at that PR that I want to merge to the 3.0.0 release branch soon if you think we should improve the documentation there, and if you think it is worth adding the fs.readFile approach.

If you would add it, I would prefer the import.meta approach as it is independent of process.cwd()

[codecov]

Codecov Report

Merging #4572 (46a5865) into master (b7e451c) will not change coverage.
The diff coverage is n/a.

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##           master    #4572   +/-   ##
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  Coverage   98.87%   98.87%           
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  Files         209      209           
  Lines        7350     7350           
  Branches     2100     2100           
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  Hits         7267     7267           
  Misses         27       27           
  Partials       56       56           

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[berniegp]

Hi! Happy to have a look yes. It probably won't be until next weekend though.

Regarding the import.meta.url changes: did you do that yourself already? I see that this PR is already merged so I'm not sure.

[lukastaegert]

No, I did no do them.

[berniegp]

I can't access lohfu:better-esm-config-file-support to open a pull request. Is this a private repository?
Or would you rather I share my findings in the PR?

[lukastaegert]

It is already merged to the 3.0 release branch in the Rollup repo, either share your findings in the old PR or create a new PR against the release branch