improve error message if this attribute of <svelte:component> is not SvelteComponent

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -416,6 +416,7 @@ export default class InlineComponentWrapper extends Wrapper {
 				}
 
 				if (${switch_value}) {
+					${component.compile_options.dev && b`@validate_svelte_component(${switch_value});`}
 					${name} = new ${switch_value}(${switch_props}(#ctx));
 
 					${munged_bindings}
@@ -460,6 +461,7 @@ export default class InlineComponentWrapper extends Wrapper {
 					}
 
 					if (${switch_value}) {
+						${component.compile_options.dev && b`@validate_svelte_component(${switch_value});`}
 						${name} = new ${switch_value}(${switch_props}(#ctx));
 
 						${munged_bindings}

src/runtime/internal/dev.ts

@@ -121,6 +121,12 @@ export function validate_void_dynamic_element(tag: undefined | string) {
 	}
 }
 
+export function validate_svelte_component(component: any) {
+	if (!(component.prototype instanceof SvelteComponent)) {
+		throw new Error('this={...} of <svelte:component> should specify a Svelte component.');
+	}
+}
+
 type Props = Record<string, any>;
 export interface SvelteComponentDev {
 	$set(props?: Props): void;

src/runtime/internal/ssr.ts

@@ -122,7 +122,7 @@ export const missing_component = {
 export function validate_component(component, name) {
 	if (!component || !component.$$render) {
 		if (name === 'svelte:component') name += ' this={...}';
-		throw new Error(`<${name}> is not a valid SSR component. You may need to review your build config to ensure that dependencies are compiled, rather than imported as pre-compiled modules`);
+		throw new Error(`<${name}> is not a valid SSR component. You may need to review your build config to ensure that dependencies are compiled, rather than imported as pre-compiled modules. Otherwise you may need to fix a <${name}>.`);
 	}
 
 	return component;