skip the noop if known to be a function

Author: Rich-Harris

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js

@@ -258,12 +258,17 @@ export function build_component(node, component_name, context, anchor = context.
 				}
 			}
 		} else if (attribute.type === 'AttachTag') {
+			const evaluated = context.state.scope.evaluate(attribute.expression);
+
 			let expression = /** @type {Expression} */ (context.visit(attribute.expression));
 
 			if (attribute.metadata.expression.has_state) {
 				expression = b.arrow(
 					[b.id('$$node')],
-					b.call(b.call('$.safe_call', expression), b.id('$$node'))
+					b.call(
+						evaluated.is_function ? expression : b.logical('||', expression, b.id('$.noop')),
+						b.id('$$node')
+					)
 				);
 			}
 

packages/svelte/src/compiler/phases/scope.js

@@ -20,6 +20,7 @@ const UNKNOWN = Symbol('unknown');
 /** Includes `BigInt` */
 export const NUMBER = Symbol('number');
 export const STRING = Symbol('string');
+export const FUNCTION = Symbol('string');
 
 /** @type {Record<string, [type: NUMBER | STRING | UNKNOWN, fn?: Function]>} */
 const globals = {
@@ -200,6 +201,13 @@ class Evaluation {
 	 */
 	is_number = true;
 
+	/**
+	 * True if the value is known to be a function
+	 * @readonly
+	 * @type {boolean}
+	 */
+	is_function = true;
+
 	/**
 	 * @readonly
 	 * @type {any}
@@ -209,7 +217,7 @@ class Evaluation {
 	/**
 	 *
 	 * @param {Scope} scope
-	 * @param {Expression} expression
+	 * @param {Expression | FunctionDeclaration} expression
 	 * @param {Set<any>} values
 	 */
 	constructor(scope, expression, values) {
@@ -500,6 +508,13 @@ class Evaluation {
 				break;
 			}
 
+			case 'ArrowFunctionExpression':
+			case 'FunctionExpression':
+			case 'FunctionDeclaration': {
+				this.values.add(FUNCTION);
+				break;
+			}
+
 			default: {
 				this.values.add(UNKNOWN);
 			}
@@ -516,6 +531,10 @@ class Evaluation {
 				this.is_number = false;
 			}
 
+			if (value !== FUNCTION) {
+				this.is_function = false;
+			}
+
 			if (value == null || value === UNKNOWN) {
 				this.is_defined = false;
 			}

packages/svelte/src/internal/client/index.js

@@ -155,7 +155,7 @@ export {
 } from './dom/operations.js';
 export { attr, clsx } from '../shared/attributes.js';
 export { snapshot } from '../shared/clone.js';
-export { noop, fallback, safe_call, to_array } from '../shared/utils.js';
+export { noop, fallback, to_array } from '../shared/utils.js';
 export {
 	invalid_default_snippet,
 	validate_dynamic_element_tag,

packages/svelte/src/internal/shared/utils.js

@@ -82,16 +82,6 @@ export function fallback(value, fallback, lazy = false) {
 		: value;
 }
 
-/**
- * @param {*} value
- */
-export function safe_call(value) {
-	if (is_function(value)) {
-		return value;
-	}
-	return noop;
-}
-
 /**
  * When encountering a situation like `let [a, b, c] = $derived(blah())`,
  * we need to stash an intermediate value that `a`, `b`, and `c` derive