[feat] explicitly set compilerOptions.hydratable to config.kit.ssr (#2024)

Author: dominikg

.changeset/nervous-items-kiss.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+explicitly set compilerOptions.hydratable to config.kit.ssr

packages/kit/src/core/build/index.js

@@ -174,7 +174,10 @@ async function build_client({
 		plugins: [
 			svelte({
 				extensions: config.extensions,
-				emitCss: !config.kit.amp
+				emitCss: !config.kit.amp,
+				compilerOptions: {
+					hydratable: !!config.kit.hydrate
+				}
 			})
 		]
 	});
@@ -463,7 +466,10 @@ async function build_server(
 		},
 		plugins: [
 			svelte({
-				extensions: config.extensions
+				extensions: config.extensions,
+				compilerOptions: {
+					hydratable: !!config.kit.hydrate
+				}
 			})
 		],
 		// this API is marked as @alpha https://github.com./vitejs/vite/blob/27785f7fcc5b45987b5f0bf308137ddbdd9f79ea/packages/vite/src/node/config.ts#L129

packages/kit/src/core/dev/index.js

@@ -136,7 +136,10 @@ class Watcher extends EventEmitter {
 			plugins: [
 				svelte({
 					extensions: this.config.extensions,
-					emitCss: !this.config.kit.amp
+					emitCss: !this.config.kit.amp,
+					compilerOptions: {
+						hydratable: !!this.config.kit.hydrate
+					}
 				})
 			],
 			publicDir: this.config.kit.files.assets,