chore: tweak render tag logic (#15109)

Author: Rich-Harris

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -706,7 +706,7 @@ function special(parser) {
 			expression: /** @type {AST.RenderTag['expression']} */ (expression),
 			metadata: {
 				dynamic: false,
-				args_with_call_expression: new Set(),
+				arguments: [],
 				path: [],
 				snippets: new Set()
 			}

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -605,7 +605,6 @@ export function analyze_component(root, source, options) {
 				has_props_rune: false,
 				component_slots: new Set(),
 				expression: null,
-				render_tag: null,
 				private_derived_state: [],
 				function_depth: scope.function_depth,
 				instance_scope: instance.scope,
@@ -677,7 +676,6 @@ export function analyze_component(root, source, options) {
 				reactive_statements: analysis.reactive_statements,
 				component_slots: new Set(),
 				expression: null,
-				render_tag: null,
 				private_derived_state: [],
 				function_depth: scope.function_depth
 			};

packages/svelte/src/compiler/phases/2-analyze/types.d.ts

@@ -19,8 +19,6 @@ export interface AnalysisState {
 	component_slots: Set<string>;
 	/** Information about the current expression/directive/block value */
 	expression: ExpressionMetadata | null;
-	/** The current {@render ...} tag, if any */
-	render_tag: null | AST.RenderTag;
 	private_derived_state: string[];
 	function_depth: number;
 

packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js

@@ -186,18 +186,6 @@ export function CallExpression(node, context) {
 			break;
 	}
 
-	if (context.state.render_tag) {
-		// Find out which of the render tag arguments contains this call expression
-		const arg_idx = unwrap_optional(context.state.render_tag.expression).arguments.findIndex(
-			(arg) => arg === node || context.path.includes(arg)
-		);
-
-		// -1 if this is the call expression of the render tag itself
-		if (arg_idx !== -1) {
-			context.state.render_tag.metadata.args_with_call_expression.add(arg_idx);
-		}
-	}
-
 	if (node.callee.type === 'Identifier') {
 		const binding = context.state.scope.get(node.callee.name);
 

packages/svelte/src/compiler/phases/2-analyze/visitors/RenderTag.js

@@ -5,6 +5,7 @@ import * as e from '../../../errors.js';
 import { validate_opening_tag } from './shared/utils.js';
 import { mark_subtree_dynamic } from './shared/fragment.js';
 import { is_resolved_snippet } from './shared/snippets.js';
+import { create_expression_metadata } from '../../nodes.js';
 
 /**
  * @param {AST.RenderTag} node
@@ -15,7 +16,8 @@ export function RenderTag(node, context) {
 
 	node.metadata.path = [...context.path];
 
-	const callee = unwrap_optional(node.expression).callee;
+	const expression = unwrap_optional(node.expression);
+	const callee = expression.callee;
 
 	const binding = callee.type === 'Identifier' ? context.state.scope.get(callee.name) : null;
 
@@ -52,5 +54,15 @@ export function RenderTag(node, context) {
 
 	mark_subtree_dynamic(context.path);
 
-	context.next({ ...context.state, render_tag: node });
+	context.visit(callee);
+
+	for (const arg of expression.arguments) {
+		const metadata = create_expression_metadata();
+		node.metadata.arguments.push(metadata);
+
+		context.visit(arg, {
+			...context.state,
+			expression: metadata
+		});
+	}
 }

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

@@ -10,20 +10,24 @@ import * as b from '../../../../utils/builders.js';
  */
 export function RenderTag(node, context) {
 	context.state.template.push('<!>');
-	const callee = unwrap_optional(node.expression).callee;
-	const raw_args = unwrap_optional(node.expression).arguments;
+
+	const expression = unwrap_optional(node.expression);
+
+	const callee = expression.callee;
+	const raw_args = expression.arguments;
 
 	/** @type {Expression[]} */
 	let args = [];
 	for (let i = 0; i < raw_args.length; i++) {
-		const raw = raw_args[i];
-		const arg = /** @type {Expression} */ (context.visit(raw));
-		if (node.metadata.args_with_call_expression.has(i)) {
+		let thunk = b.thunk(/** @type {Expression} */ (context.visit(raw_args[i])));
+		const { has_call } = node.metadata.arguments[i];
+
+		if (has_call) {
 			const id = b.id(context.state.scope.generate('render_arg'));
-			context.state.init.push(b.var(id, b.call('$.derived_safe_equal', b.thunk(arg))));
+			context.state.init.push(b.var(id, b.call('$.derived_safe_equal', thunk)));
 			args.push(b.thunk(b.call('$.get', id)));
 		} else {
-			args.push(b.thunk(arg));
+			args.push(thunk);
 		}
 	}
 

packages/svelte/src/compiler/types/template.d.ts

@@ -166,7 +166,7 @@ export namespace AST {
 		/** @internal */
 		metadata: {
 			dynamic: boolean;
-			args_with_call_expression: Set<number>;
+			arguments: ExpressionMetadata[];
 			path: SvelteNode[];
 			/** The set of locally-defined snippets that this render tag could correspond to,
 			 * used for CSS pruning purposes */