chore: avoid creating unnecessary thunks (#9841)

Co-authored-by: Rich Harris <[email protected]>

.changeset/poor-seahorses-flash.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: avoid creating thunk for call expressions when appropriate

packages/svelte/src/compiler/utils/builders.js

@@ -370,9 +370,18 @@ export function template(elements, expressions) {
 
 /**
  * @param {import('estree').Expression | import('estree').BlockStatement} expression
- * @returns {import('estree').ArrowFunctionExpression}
+ * @returns {import('estree').Expression}
  */
 export function thunk(expression) {
+	if (
+		expression.type === 'CallExpression' &&
+		expression.callee.type !== 'Super' &&
+		expression.callee.type !== 'MemberExpression' &&
+		expression.arguments.length === 0
+	) {
+		return expression.callee;
+	}
+
 	return arrow([], expression);
 }
 

packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js

@@ -21,9 +21,9 @@ export default function Main($$anchor, $$props) {
 	var custom_element_1 = $.sibling($.sibling(svg_1));
 
 	/* Update */
-	$.attr_effect(div, "foobar", () => y());
-	$.attr_effect(svg_1, "viewBox", () => y());
-	$.set_custom_element_data_effect(custom_element_1, "fooBar", () => y());
+	$.attr_effect(div, "foobar", y);
+	$.attr_effect(svg_1, "viewBox", y);
+	$.set_custom_element_data_effect(custom_element_1, "fooBar", y);
 
 	var node_foobar;
 	var svg_viewBox;
@@ -45,4 +45,4 @@ export default function Main($$anchor, $$props) {
 
 	$.close_frag($$anchor, fragment);
 	$.pop();
-}
+}

packages/svelte/tests/snapshot/samples/svelte-element/_expected/client/index.svelte.js

@@ -11,7 +11,7 @@ export default function Svelte_element($$anchor, $$props) {
 	var fragment = $.comment($$anchor);
 	var node = $.child_frag(fragment);
 
-	$.element(node, () => tag());
+	$.element(node, tag);
 	$.close_frag($$anchor, fragment);
 	$.pop();
 }