Add hooks for HMR support (sveltejs#2377)

src/compiler/compile/render_dom/index.ts

@@ -94,7 +94,7 @@ export default function dom(
 	const body = [];
 
 	const not_equal = component.component_options.immutable ? `@not_equal` : `@safe_not_equal`;
-	let dev_props_check;
+	let dev_props_check; let inject_state; let capture_state;
 
 	props.forEach(x => {
 		const variable = component.var_lookup.get(x.name);
@@ -151,6 +151,21 @@ export default function dom(
 				}`)}
 			`;
 		}
+
+		capture_state = (uses_props || writable_props.length > 0) ? deindent`
+			() => {
+				return { ${component.vars.map(prop => prop.name).join(", ")} };
+			}
+		` : null;
+
+		inject_state = (uses_props || writable_props.length > 0) ? deindent`
+			${$$props} => {
+				${uses_props && component.invalidate('$$props', `$$props = @assign(@assign({}, $$props), $$new_props)`)}
+				${component.vars.map(prop => deindent`
+					if ('${prop.name}' in $$props) ${component.invalidate(prop.name, `${prop.name} = ${$$props}.${prop.name}`)};
+				`)}
+			}
+		` : null;
 	}
 
 	// instrument assignments
@@ -430,6 +445,10 @@ export default function dom(
 
 				${set && `$$self.$set = ${set};`}
 
+				${capture_state && `$$self.$capture_state = ${capture_state};`}
+
+				${inject_state && `$$self.$inject_state = ${inject_state};`}
+
 				${injected.length && `let ${injected.join(', ')};`}
 
 				${reactive_declarations.length > 0 && deindent`