export map breaks rollup plugin, others trying to import/require ('svelte/package.json')

[FredKSchott]

Congrats on releasing the new export map! Quick issue spotted: Node.js doesn't default to include the package.json file as part of your package, meaning tooling/consumers can't `require('svelte/package.json'). The Rollup plugin currently does this, as do many others.

Snowpack's Svelte template is broken as a result.

The fix is to add this to your export map:

"exports": {
+    "./package.json": "./package.json"
}

[FredKSchott]

Since this went out as a patch release, I'd recommend a quick follow up patch to add.

[bradak1]

** RUNNING ROLLUP: prod: true **
Bundling: dynamic
[!] Error: Package subpath './package.json' is not defined by "exports" in <path>/site/node_modules/svelte/package.json
Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './package.json' is not defined by "exports" in <path>/site/node_modules/svelte/package.json

[FredKSchott]

@MylesBorins is there a thread where this "package.json not automatically included in export map" behavior is already being discussed? I've seen this issue bite so many packages trying to upgrade to an export map, and it's only going to keep happening.

If it hasn't been proposed yet, I'd like to start a thread.

[Conduitry]

Thanks! Fixed in 3.29.6 - https://unpkg.com/svelte@3.29.6/package.json

[bradak1]

not fixed, now I get error for compiler.js:

** RUNNING ROLLUP: prod: true **
Bundling: dynamic
[!] Error: Package subpath './compiler.js' is not defined by "exports" in <path>/site/node_modules/svelte/package.json
Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './compiler.js' is not defined by "exports" in <path>/site/node_modules/svelte/package.json

[Conduitry]

The export map contains

    "./compiler": {
      "import": "./compiler.mjs",
      "require": "./compiler.js"
    },

Which I assume means that things need to use svelte/compiler and that something is using svelte/compiler.js. Do we need to also support svelte/compiler.js? In your case, what's trying to import/require that? Is it the Rollup plugin?

[bradak1]

yes, rollup

[Conduitry]

Yeah, I see it at https://github.com/sveltejs/rollup-plugin-svelte/blob/65fbfc7824b7e86e546ed064bf6d94b87ebb7b37/index.js#L15 - This will be fixed in the next major version of the Rollup plugin, but we should either also support importing from svelte/compiler.js in the export map, or we should backport a fix to 6.x of the Rollup plugin to use svelte/compiler. I don't know which is more proper.

[Conduitry]

This should be fixed with rollup-plugin-svelte@6.1.1.

[bradak1]

yup, it's fixed. Thx!

[MylesBorins]

@MylesBorins is there a thread where this "package.json not automatically included in export map" behavior is already being discussed? I've seen this issue bite so many packages trying to upgrade to an export map, and it's only going to keep happening.

If it hasn't been proposed yet, I'd like to start a thread.

Oh hi!

There is a historical thread nodejs/modules#445

TL;DR while it is "unexpected" today, the general intent of exports is to make the contract for a module explicit, and the general thought was that exposing the package.json as part of the module API should be opt-in by the module author

Making a carve out in exports for package.json imho complicates the API, and while there is a mismatch with current expectation, it would be more confusing in the long term.

One solution that has been discussion is exposing an API in Node.js core that would make it easy for tools / module consumers to easily get the path to a package.json. This is being discussed in nodejs/node#49445

With this type of util api you would be able to do something like

import { readFile } from 'fs/promises';
import { resolvePackageRoot } from 'module';
const svelteRoot = await resolvePackageRoot('svelte');
const svelteJSON = JSON.parse(await readFile(svelteRoot + '/package.json'));

While this is definitely more verbose it would be consistent and reliable for all packages while still allowing a module author to not make the package.json part of their packages API by default.

[FredKSchott]

Thanks @MylesBorins, responded in historical thread.