chore: backport fixes (#917)

* fix: disable hmr when explicitly disabled in vite config (#913)

* feat: disable hmr when running in vitest by default

* refactor: use vite server.hmr config instead that is set by vitest

* fix: enforce hmr false, update changeset

(cherry picked from commit f7409c8)

* fix: ensure vite config is only resolved once in lazy init of vitePreprocess (#912)

* fix: ensure vite config is only resolved once

* fix: add back inlined function to please ts

(cherry picked from commit 1211f97)

* fix: remove extraneous checks for viteConfig.server

.changeset/rare-turkeys-mate.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+fix: ensure vite config is only resolved once during lazy init of vitePreprocess

.changeset/strong-cherries-know.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+fix: disable hmr when vite config server.hmr is false

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

@@ -61,29 +61,16 @@ function viteScript() {
  * @returns {{ style: import('svelte/compiler').Preprocessor }}
  */
 function viteStyle(config = {}) {
-	/** @type {CssTransform} */
-	let transform;
+	/** @type {Promise<CssTransform> | CssTransform} */
+	let cssTransform;
 	/** @type {import('svelte/compiler').Preprocessor} */
 	const style = async ({ attributes, content, filename = '' }) => {
 		const ext = attributes.lang ? `.${attributes.lang}` : '.css';
 		if (attributes.lang && !isCSSRequest(ext)) return;
-		if (!transform) {
-			/** @type {import('vite').ResolvedConfig} */
-			let resolvedConfig;
-			// @ts-expect-error special prop added if running in v-p-s
-			if (style.__resolvedConfig) {
-				// @ts-expect-error
-				resolvedConfig = style.__resolvedConfig;
-			} else if (isResolvedConfig(config)) {
-				resolvedConfig = config;
-			} else {
-				resolvedConfig = await resolveConfig(
-					config,
-					process.env.NODE_ENV === 'production' ? 'build' : 'serve'
-				);
-			}
-			transform = getCssTransformFn(resolvedConfig);
+		if (!cssTransform) {
+			cssTransform = createCssTransform(style, config).then((t) => (cssTransform = t));
 		}
+		const transform = await cssTransform;
 		const suffix = `${lang_sep}${ext}`;
 		const moduleId = `${filename}${suffix}`;
 		const { code, map, deps } = await transform(content, moduleId);
@@ -102,12 +89,27 @@ function viteStyle(config = {}) {
 }
 
 /**
- * @param {import('vite').ResolvedConfig} config
- * @returns {CssTransform}
+ * @param {import('svelte/compiler').Preprocessor} style
+ * @param {import('vite').ResolvedConfig | import('vite').InlineConfig} config
+ * @returns {Promise<CssTransform>}
  */
-function getCssTransformFn(config) {
+async function createCssTransform(style, config) {
+	/** @type {import('vite').ResolvedConfig} */
+	let resolvedConfig;
+	// @ts-expect-error special prop added if running in v-p-s
+	if (style.__resolvedConfig) {
+		// @ts-expect-error
+		resolvedConfig = style.__resolvedConfig;
+	} else if (isResolvedConfig(config)) {
+		resolvedConfig = config;
+	} else {
+		resolvedConfig = await resolveConfig(
+			config,
+			process.env.NODE_ENV === 'production' ? 'build' : 'serve'
+		);
+	}
 	return async (code, filename) => {
-		return preprocessCSS(code, filename, config);
+		return preprocessCSS(code, filename, resolvedConfig);
 	};
 }
 

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

@@ -199,13 +199,15 @@ export function resolveOptions(preResolveOptions, viteConfig, cache) {
 			dev: !viteConfig.isProduction
 		}
 	};
+	const hot =
+		!viteConfig.isProduction && !preResolveOptions.isBuild && viteConfig.server.hmr !== false;
 	if (isSvelte5) {
 		if (isSvelte5WithHMRSupport) {
 			// @ts-expect-error svelte4 does not have hmr option
-			defaultOptions.compilerOptions.hmr = !viteConfig.isProduction;
+			defaultOptions.compilerOptions.hmr = hot;
 		}
 	} else {
-		defaultOptions.hot = viteConfig.isProduction
+		defaultOptions.hot = !hot
 			? false
 			: {
 					injectCss: css === 'injected',
@@ -224,7 +226,7 @@ export function resolveOptions(preResolveOptions, viteConfig, cache) {
 	removeIgnoredOptions(merged);
 	handleDeprecatedOptions(merged);
 	addExtraPreprocessors(merged, viteConfig);
-	enforceOptionsForHmr(merged);
+	enforceOptionsForHmr(merged, viteConfig);
 	enforceOptionsForProduction(merged);
 	// mergeConfigs would mangle functions on the stats class, so do this afterwards
 	if (log.debug.enabled && isDebugNamespaceEnabled('stats')) {
@@ -235,8 +237,15 @@ export function resolveOptions(preResolveOptions, viteConfig, cache) {
 
 /**
  * @param {import('../types/options.d.ts').ResolvedOptions} options
+ * @param {import('vite').ResolvedConfig} viteConfig
  */
-function enforceOptionsForHmr(options) {
+function enforceOptionsForHmr(options, viteConfig) {
+	if (options.hot && viteConfig.server.hmr === false) {
+		log.warn(
+			'vite config server.hmr is false but hot is true. Forcing hot to false as it would not work.'
+		);
+		options.hot = false;
+	}
 	if (isSvelte5) {
 		if (options.hot && isSvelte5WithHMRSupport) {
 			log.warn(