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

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/e2e-tests/kit-node/svelte.config.js

@@ -1,10 +1,8 @@
 import node from '@sveltejs/adapter-node';
-
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
 	kit: {
 		adapter: node()
 	}
 };
-
 export default config;

packages/e2e-tests/vite-ssr-esm/vite.config.js

@@ -3,13 +3,7 @@ import { svelte } from '@sveltejs/vite-plugin-svelte';
 
 export default defineConfig(({ command, mode }) => {
 	return {
-		plugins: [
-			svelte({
-				compilerOptions: {
-					hydratable: true /* required for clientside hydration */
-				}
-			})
-		],
+		plugins: [svelte()],
 		build: {
 			target: 'esnext',
 			minify: false,

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

@@ -201,7 +201,11 @@ export function resolveOptions(preResolveOptions, viteConfig, cache) {
 		compilerOptions: {
 			css,
 			dev: !viteConfig.isProduction,
-			hmr: !viteConfig.isProduction && !preResolveOptions.isBuild
+			hmr:
+				!viteConfig.isProduction &&
+				!preResolveOptions.isBuild &&
+				viteConfig.server &&
+				viteConfig.server.hmr !== false
 		}
 	};
 
@@ -217,7 +221,7 @@ 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')) {
@@ -228,15 +232,22 @@ 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) {
 		log.warn(
 			'svelte 5 has hmr integrated in core. Please remove the vitePlugin.hot option and use compilerOptions.hmr instead'
 		);
 		delete options.hot;
 		options.compilerOptions.hmr = true;
 	}
+	if (options.compilerOptions.hmr && viteConfig.server?.hmr === false) {
+		log.warn(
+			'vite config server.hmr is false but compilerOptions.hmr is true. Forcing compilerOptions.hmr to false as it would not work.'
+		);
+		options.compilerOptions.hmr = false;
+	}
 }
 
 /**
@@ -264,7 +275,7 @@ function enforceOptionsForProduction(options) {
  */
 function removeIgnoredOptions(options) {
 	const ignoredCompilerOptions = ['generate', 'format', 'filename'];
-	if (options.hot && options.emitCss) {
+	if (options.compilerOptions.hmr && options.emitCss) {
 		ignoredCompilerOptions.push('cssHash');
 	}
 	const passedCompilerOptions = Object.keys(options.compilerOptions || {});