Fixed postcss plugin resolution for consumers of the design system config

[9larsons]

apps/admin-x-settings/postcss.config.cjs re-exports the design system's config. That config named its plugins as strings, and postcss-load-config resolves string plugin names relative to the searchPath — the directory the consuming build discovered a config in — not the file that declared the list.

So the plugin names resolve from apps/admin-x-settings, which declares none of postcss-import, @tailwindcss/postcss or autoprefixer. Under pnpm's strict isolation they are not linked there, and none of the three resolve from that directory.

Why now, if the build is green?

It is currently masked. The plugins genuinely cannot be resolved from admin-x-settings — that is verifiable with a require.resolve probe from that directory — so today's successful build depends on the loader not using the consumer as its anchor. That is one loader change away from breaking, and it broke in a real working tree.

The fix

require() the three plugins inside apps/admin-x-design-system/postcss.config.cjs and pass instances rather than names, so resolution is anchored to the package that declares them. No string resolution happens at the consumer at all. postcss(fn) auto-invokes factories carrying .postcss === true, which all three do, so postcssImport() is exactly equivalent to 'postcss-import': {}.

Alternatives rejected:

• Adding postcss-import et al as devDependencies of each consumer — papers over the resolution bug and has to be repeated for every package that reuses the config.
• Deleting the postcss configs — they are not vestigial. The centralized Tailwind v4 pipeline applies to apps/admin's @tailwindcss/vite setup; admin-x-settings still builds a standalone bundle through adminXViteConfig, which has no Tailwind plugin. Its src/styles/index.css does @import 'tailwindcss/utilities.css', and postcss expands that into ~470 kB of real utilities. Deleting the config would silently strip every utility class from that bundle.

Verification

• pnpm --filter @tryghost/admin-x-settings build — exit 0
• pnpm --filter @tryghost/admin-x-settings lint and pnpm --filter @tryghost/admin-x-design-system lint — exit 0
• NX_NO_CLOUD=true pnpm nx build @tryghost/admin --skip-nx-cache — exit 0, all 15 dependent tasks genuinely executed. (The plain nx reset && nx build run replayed 9/16 tasks from Nx Cloud's remote cache, which would have masked a failure.)
• Emitted CSS is unchanged. The build was first confirmed deterministic (two unchanged builds → identical checksum) so the comparison is meaningful. The postcss product is byte-identical at 469,587 bytes, and all 31 files of apps/admin-x-settings/dist match before and after.

Same three plugins, same order, same empty options — only where they resolve from has changed.

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Reviewing files that changed from the base of the PR and between 65fc69d and a77bd1d.

📒 Files selected for processing (1)

• apps/admin-x-design-system/postcss.config.cjs

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Walkthrough

The PostCSS configuration file for admin-x-design-system was modified to change how plugins are declared. Instead of an object mapping plugin names to configuration, the file now requires each plugin (postcss-import, @tailwindcss/postcss, autoprefixer) and defines the exports as an array of instantiated plugin functions. Explanatory comments were added describing why plugins are instantiated locally, related to resolution behavior of postcss-load-config and consistency with how admin-x-settings re-exports the configuration.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: fixing PostCSS plugin resolution for design system consumers.
Description check	✅ Passed	The description is directly about the PostCSS config resolution fix and matches the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch slars/fix-admin-x-settings-postcss-resolution

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☁️ Nx Cloud last updated this comment at 2026-07-08 20:32:25 UTC