on second thoughts

src/compiler/compile/nodes/Action.ts

@@ -17,7 +17,7 @@ export default class Action extends Node {
 		component.qualify(info.name);
 
 		this.expression = info.expression
-			? new Expression(component, this, scope, info.expression, true)
+			? new Expression(component, this, scope, info.expression)
 			: null;
 
 		this.uses_context = this.expression && this.expression.uses_context;

src/compiler/compile/nodes/shared/Expression.ts

@@ -146,11 +146,11 @@ export default class Expression {
 
 						contextual_dependencies.add(name);
 
-						if (!function_expression || !lazy) {
+						if (!lazy) {
 							template_scope.dependencies_for_name.get(name).forEach(name => dependencies.add(name));
 						}
 					} else {
-						if (!function_expression || !lazy) {
+						if (!lazy) {
 							dependencies.add(name);
 						}
 

test/js/samples/action-custom-event-handler/expected.js

@@ -23,7 +23,12 @@ function create_fragment(ctx) {
 			foo_action = foo.call(null, button, ctx.foo_function) || {};
 		},
 
-		p: noop,
+		p(changed, ctx) {
+			if (typeof foo_action.update === 'function' && changed.bar) {
+				foo_action.update.call(null, ctx.foo_function);
+			}
+		},
+
 		i: noop,
 		o: noop,