fix(server-bundle): keep the with key on externalized icon JSON imports

[agantelin]

🔗 Linked issue

Resolves #522

📚 Description

externalizeIconsJson generates import('@iconify-json/…/icons.json', { with: { type: 'json' } })
(src/bundle-server.ts:57), but Rollup 4 re-prints the attributes of external modules with its own
default key, assert — and Node.js removed assert in v22, so the icon API 500s with
ERR_IMPORT_ATTRIBUTE_MISSING while the build stays green. Same user-visible error as #186, which
#187 fixed by adding the attribute; this time it's written correctly and lost downstream.

Rollup only flips that default in v5 (rollup/rollup#6248, merged to rollup-5, unreleased). Nitro
has the same gap and I've filed nitrojs/nitro#4518 for it, but a fix there won't reach anyone on a
released Nitro — and this module is the one that creates the external import. So it sets the key
itself, from the plugin it already installs, via outputOptions: ||= leaves an explicit user
setting alone, it works whether the build has one output or several, and nothing outside this
plugin is touched.

After this, the README's promise — "in the final build, it will contain statements like
() => import('@iconify-json/ph/icons.json', { with: { type: 'json' } })" — holds again.

Verification

In playgrounds/nuxt, with serverBundle: { externalizeIconsJson: true } and pnpm play:build:

# before
.output/server/chunks/_/nitro.mjs: import('@iconify-json/ph/icons.json', { assert: { type: 'json' } })
# after
.output/server/chunks/_/nitro.mjs: import('@iconify-json/ph/icons.json', { with: { type: 'json' } })

The underlying Rollup/Nitro behaviour, on plain Nitro without Nuxt (so the 500 and the 200 are easy
to see): https://github.com/agantelin/nitro-import-attributes-repro

No unit test: the hook this touches is the nitro:config one, which the current suite doesn't
exercise, and the playground build above is the honest check. Glad to add one if you'd like it
covered.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/icon@523

commit: dc36a7c

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 29f3e917-3c5e-419c-9f60-8c3cc008de8c

📥 Commits

Reviewing files that changed from the base of the PR and between e062607 and dc36a7c.

📒 Files selected for processing (1)

• src/module.ts

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📝 Walkthrough

Walkthrough

The module adds a Rollup outputOptions hook. The hook preserves an explicit importAttributesKey value and defaults it to with when unset. Generated external-module imports therefore use the configured import-attribute key.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the fix for preserving the with key on externalized icon JSON imports.
Description check	✅ Passed	The description accurately explains the Rollup behavior, runtime failure, implementation, and verification for the changeset.
Linked Issues check	✅ Passed	The change configures Rollup to use with while preserving explicit settings, satisfying issue #522.
Out of Scope Changes check	✅ Passed	The changes are limited to the Rollup output configuration required to fix externalized icon JSON imports.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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