Priority policy

compose() accepts a pre_order policy and a diagnostics switch.

compose(plugins, {
	pre_order: "strip",
	diagnostics: true,
});

strip

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The default removes plugin-level enforce: "pre" and hook-level order: "pre" from load, resolveId, transform, and transformIndexHtml. Other plugin fields and hook properties are copied unchanged.

Use this when the array order is the source of truth:

compose([syntax_transform(), sveltekit()]);

warn

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The "warn" policy preserves pre priority but records every place that requested it. The diagnostics plugin logs those decisions after Vite resolves configuration.

compose([legacy_plugin(), sveltekit()], {
	pre_order: "warn",
});

This is useful while adopting composer because it reveals which plugins still reorder themselves without changing their behavior.

preserve

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The "preserve" policy leaves pre priority untouched and records no change. Use it when a plugin's documented contract genuinely requires Vite's pre phase.

compose([required_pre_plugin(), sveltekit()], {
	pre_order: "preserve",
});

You can also keep a priority-sensitive plugin outside the composed list:

export default defineConfig({
	plugins: [required_pre_plugin(), ...compose([plugin_a(), sveltekit()])],
});

Set diagnostics: false to omit the appended diagnostics plugin. That changes logging only; normalization still follows pre_order.