move store subscriptions into a helper. broke a bunch of stuff, bear with me

src/compile/Component.ts

@@ -183,7 +183,11 @@ export default class Component {
 				writable: true
 			});
 
-			this.add_reference(name.slice(1));
+			const subscribable_name = name.slice(1);
+			this.add_reference(subscribable_name);
+
+			const variable = this.var_lookup.get(subscribable_name);
+			variable.subscribable = true;
 		} else if (!this.ast.instance) {
 			this.add_var({
 				name,
@@ -213,6 +217,11 @@ export default class Component {
 		return this.aliases.get(name);
 	}
 
+	helper(name: string) {
+		this.helpers.add(name);
+		return this.alias(name);
+	}
+
 	generate(result: string) {
 		const { compileOptions, name } = this;
 		const { format = 'esm' } = compileOptions;
@@ -641,6 +650,9 @@ export default class Component {
 				});
 
 				this.add_reference(name.slice(1));
+
+				const variable = this.var_lookup.get(name.slice(1));
+				variable.subscribable = true;
 			} else {
 				this.add_var({
 					name,
@@ -783,8 +795,7 @@ export default class Component {
 
 									// can't use the @ trick here, because we're
 									// manipulating the underlying magic string
-									component.helpers.add('exclude_internal_props');
-									const exclude_internal_props = component.alias('exclude_internal_props');
+									const exclude_internal_props = component.helper('exclude_internal_props');
 
 									const suffix = code.original[declarator.end] === ';'
 										? ` = ${exclude_internal_props}($$props)`
@@ -799,7 +810,9 @@ export default class Component {
 
 								if (variable.export_name) {
 									has_exports = true;
-								} else {
+								}
+
+								if (!variable.export_name || variable.subscribable) {
 									has_only_exports = false;
 								}
 							});

src/compile/render-dom/index.ts

@@ -202,6 +202,38 @@ export default function dom(
 					component.has_reactive_assignments = true;
 				}
 
+				else if (node.type === 'VariableDeclarator') {
+					const names = extractNames(node.id);
+					names.forEach(name => {
+						const owner = scope.findOwner(name);
+						if (owner && owner !== component.instance_scope) return;
+
+						const variable = component.var_lookup.get(name);
+						if (variable && variable.subscribable) {
+							const value = `$${name}`;
+
+							const subscribe = component.helper('subscribe');
+
+							const index = parent.declarations.indexOf(node);
+							const next = parent.declarations[index + 1];
+
+							let insert = `${subscribe}($$self, ${name}, $$value => { ${value} = $$value; $$invalidate('${value}', ${value}) })`;
+							if (component.compileOptions.dev) {
+								const validate_store = component.helper('validate_store');
+								insert = `${validate_store}(${name}, '${name}'); ${insert}`;
+							}
+
+							// initialise store value here
+							if (next) {
+								code.overwrite(node.end, next.start, `; ${insert}; ${parent.kind} `);
+							} else {
+								// final (or only) declarator
+								code.appendLeft(node.end, `; ${insert}`);
+							}
+						}
+					});
+				}
+
 				if (pending_assignments.size > 0) {
 					if (node.type === 'ArrowFunctionExpression') {
 						const insert = Array.from(pending_assignments).map(name => `$$invalidate('${name}', ${name})`).join(';');
@@ -310,12 +342,12 @@ export default function dom(
 			: null
 	);
 
-	const reactive_store_subscriptions = reactive_stores.length > 0 && reactive_stores
+	const reactive_store_subscriptions = reactive_stores
+		.filter(store => component.var_lookup.get(store.name).hoistable)
 		.map(({ name }) => deindent`
 			${component.compileOptions.dev && `@validate_store(${name.slice(1)}, '${name.slice(1)}');`}
-			$$self.$$.on_destroy.push(${name.slice(1)}.subscribe($$value => { ${name} = $$value; $$invalidate('${name}', ${name}); }));
-		`)
-		.join('\n\n');
+			@subscribe($$self, ${name.slice(1)}, $$value => { ${name} = $$value; $$invalidate('${name}', ${name}); });
+		`);
 
 	if (has_definition) {
 		const reactive_declarations = component.reactive_declarations.map(d => {
@@ -346,6 +378,8 @@ export default function dom(
 			function ${definition}(${args.join(', ')}) {
 				${reactive_stores.length > 0 && `let ${reactive_stores.map(store => store.name).join(', ')};`}
 
+				${reactive_store_subscriptions}
+
 				${user_code}
 
 				${renderer.slots.size && `let { ${[...renderer.slots].map(name => `$$slot_${sanitize(name)}`).join(', ')}, $$scope } = $$props;`}
@@ -354,8 +388,6 @@ export default function dom(
 
 				${component.partly_hoisted.length > 0 && component.partly_hoisted.join('\n\n')}
 
-				${reactive_store_subscriptions}
-
 				${set && `$$self.$set = ${set};`}
 
 				${reactive_declarations.length > 0 && deindent`

src/compile/render-ssr/index.ts

@@ -3,6 +3,8 @@ import Component from '../Component';
 import { CompileOptions } from '../../interfaces';
 import { stringify } from '../../utils/stringify';
 import Renderer from './Renderer';
+import { walk } from 'estree-walker';
+import { extractNames } from '../../utils/annotateWithScopes';
 
 export default function ssr(
 	component: Component,
@@ -22,11 +24,63 @@ export default function ssr(
 		{ code: null, map: null } :
 		component.stylesheet.render(options.filename, true);
 
-	let user_code;
+	// insert store values
+	if (component.ast.instance) {
+		let scope = component.instance_scope;
+		let map = component.instance_scope_map;
+
+		walk(component.ast.instance.content, {
+			enter: (node, parent) => {
+				if (map.has(node)) {
+					scope = map.get(node);
+				}
+			},
+
+			leave(node, parent) {
+				if (map.has(node)) {
+					scope = scope.parent;
+				}
+
+				if (node.type === 'VariableDeclarator') {
+					const names = extractNames(node.id);
+					names.forEach(name => {
+						const owner = scope.findOwner(name);
+						if (owner && owner !== component.instance_scope) return;
+
+						const variable = component.var_lookup.get(name);
+						if (variable && variable.subscribable) {
+							const value = `$${name}`;
+
+							const get_store_value = component.helper('get_store_value');
+
+							const index = parent.declarations.indexOf(node);
+							const next = parent.declarations[index + 1];
+
+							let insert = `const ${value} = ${get_store_value}(${name});`;
+							if (component.compileOptions.dev) {
+								const validate_store = component.helper('validate_store');
+								insert = `${validate_store}(${name}, '${name}'); ${insert}`;
+							}
+
+							// initialise store value here
+							if (next) {
+								component.code.overwrite(node.end, next.start, `; ${insert}; ${parent.kind} `);
+							} else {
+								// final (or only) declarator
+								component.code.appendLeft(node.end, `; ${insert}`);
+							}
+						}
+					});
+				}
+			}
+		});
+	}
 
 	// TODO remove this, just use component.vars everywhere
 	const props = component.vars.filter(variable => !variable.module && variable.export_name && variable.export_name !== component.componentOptions.props_object);
 
+	let user_code;
+
 	if (component.javascript) {
 		component.rewrite_props();
 		user_code = component.javascript;
@@ -38,13 +92,15 @@ export default function ssr(
 	}
 
 	const reactive_stores = component.vars.filter(variable => variable.name[0] === '$');
-	const reactive_store_values = reactive_stores.map(({ name }) => {
-		const assignment = `const ${name} = @get_store_value(${name.slice(1)});`;
-
-		return component.compileOptions.dev
-			? `@validate_store(${name.slice(1)}, '${name.slice(1)}'); ${assignment}`
-			: assignment;
-	});
+	const reactive_store_values = reactive_stores
+		.filter(store => component.var_lookup.get(store.name).hoistable)
+		.map(({ name }) => {
+			const assignment = `const ${name} = @get_store_value(${name.slice(1)});`;
+
+			return component.compileOptions.dev
+				? `@validate_store(${name.slice(1)}, '${name.slice(1)}'); ${assignment}`
+				: assignment;
+		});
 
 	// TODO only do this for props with a default value
 	const parent_bindings = component.javascript

src/interfaces.ts

@@ -89,4 +89,5 @@ export interface Var {
 	internal?: boolean; // event handlers, bindings
 	initialised?: boolean;
 	hoistable?: boolean;
+	subscribable?: boolean;
 }

src/internal/utils.js

@@ -47,6 +47,10 @@ export function validate_store(store, name) {
 	}
 }
 
+export function subscribe(component, store, callback) {
+	component.$$.on_destroy.push(store.subscribe(callback));
+}
+
 export function create_slot(definition, ctx, fn) {
 	if (definition) {
 		const slot_ctx = get_slot_context(definition, ctx, fn);

test/runtime/samples/store-auto-subscribe-immediate-multiple-vars/_config.js

@@ -0,0 +1,9 @@
+export default {
+	html: `
+		<p>42</p>
+	`,
+
+	async test({ assert, component }) {
+		assert.equal(component.initial_foo, 42);
+	}
+};

test/runtime/samples/store-auto-subscribe-immediate-multiple-vars/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	import { writable } from 'svelte/store';
+	const foo = writable(42), bar = 'something else';
+	export let initial_foo = $foo;
+</script>
+
+<p>{initial_foo}</p>