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)

Author: dominikg

.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/utils/options.js

@@ -199,13 +199,18 @@ export function resolveOptions(preResolveOptions, viteConfig, cache) {
 			dev: !viteConfig.isProduction
 		}
 	};
+	const hot =
+		!viteConfig.isProduction &&
+		!preResolveOptions.isBuild &&
+		viteConfig.server &&
+		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 +229,7 @@ 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 +240,15 @@ 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(