chore: deprecate plugin.api.sveltePreprocess

Author: dominikg

.changeset/two-facts-sink.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+deprecate `plugin.api.sveltePreprocess`

docs/faq.md

@@ -82,19 +82,7 @@ However, `cssHash` is respected in production builds as HMR is a dev-only featur
 
 ### How do I add a Svelte preprocessor from a Vite plugin?
 
-If you are building a Vite plugin that transforms CSS or JS, you can add a `api.sveltePreprocess: PreprocessorGroup` to your Vite plugin definition and it will be added to the list of Svelte preprocessors used at runtime.
-
-```js
-const vitePluginCoolCss = {
-  name: 'vite-plugin-coolcss',
-  api: {
-    sveltePreprocess: {
-      /* your PreprocessorGroup here */
-    }
-  }
-  /*... your cool css plugin implementation here .. */
-};
-```
+You don't have to anymore. See [advanced usage](advanced-usage.md) for examples how to put transform hooks before or after Svelte preprocess or compile
 
 ### What is going on with Vite and `Pre-bundling dependencies:`?
 

packages/vite-plugin-svelte/src/utils/preprocess.js

@@ -15,28 +15,13 @@ function buildExtraPreprocessors(options, config) {
 	/** @type {import('svelte/compiler').PreprocessorGroup[]} */
 	const appendPreprocessors = [];
 
-	// @ts-expect-error not typed
-	const pluginsWithPreprocessorsDeprecated = config.plugins.filter((p) => p?.sveltePreprocess);
+	const pluginsWithPreprocessorsDeprecated = config.plugins.filter((p) => p.api?.sveltePreprocess);
 	if (pluginsWithPreprocessorsDeprecated.length > 0) {
 		log.warn(
-			`The following plugins use the deprecated 'plugin.sveltePreprocess' field. Please contact their maintainers and ask them to move it to 'plugin.api.sveltePreprocess': ${pluginsWithPreprocessorsDeprecated
+			`The following plugins use the deprecated 'plugin.api.sveltePreprocess' field. Please contact their maintainers and ask them to use a vite plugin transform instead: ${pluginsWithPreprocessorsDeprecated
 				.map((p) => p.name)
 				.join(', ')}`
 		);
-		// patch plugin to avoid breaking
-		pluginsWithPreprocessorsDeprecated.forEach((p) => {
-			if (!p.api) {
-				p.api = {};
-			}
-			if (p.api.sveltePreprocess === undefined) {
-				// @ts-expect-error not typed
-				p.api.sveltePreprocess = p.sveltePreprocess;
-			} else {
-				log.error(
-					`ignoring plugin.sveltePreprocess of ${p.name} because it already defined plugin.api.sveltePreprocess.`
-				);
-			}
-		});
 	}
 	/** @type {import('vite').Plugin[]} */
 	const pluginsWithPreprocessors = config.plugins.filter((p) => p?.api?.sveltePreprocess);