improve static considertaion for contextual variable

Author: tanhauhau

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

@@ -175,6 +175,15 @@ export default class Expression {
 		});
 	}
 
+	dynamic_contextual_dependencies() {
+		return Array.from(this.contextual_dependencies).filter(name => {
+			return Array.from(this.template_scope.dependencies_for_name.get(name)).some(variable_name => {
+				const variable = this.component.var_lookup.get(variable_name);
+				return is_dynamic(variable);
+			});
+		});
+	}
+
 	// TODO move this into a render-dom wrapper?
 	manipulate(block?: Block, ctx?: string | void) {
 		// TODO ideally we wouldn't end up calling this method

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

@@ -19,7 +19,7 @@ export default class Tag extends Node {
 		);
 	}
 	is_dependencies_static() {
-		return this.expression.contextual_dependencies.size === 0 && this.expression.dynamic_dependencies().length === 0;
+		return this.expression.dynamic_contextual_dependencies().length === 0 && this.expression.dynamic_dependencies().length === 0;
 	}
 	check_if_content_dynamic() {
 		if (!this.is_dependencies_static()) {