chore: better `get_rune` helper (#9594)

* chore: add $effect.active rune

* chore: add $effect.active rune

* WIP

* allow get_rune to return a keypath

* oops

---------

Co-authored-by: Dominic Gannaway <dg@domgan.com>
Co-authored-by: Rich Harris <rich.harris@vercel.com>

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

@@ -503,24 +503,19 @@ function validate_call_expression(node, scope, path) {
 		error(node, rune === '$derived' ? 'invalid-derived-location' : 'invalid-state-location');
 	}
 
-	if (rune === '$effect') {
-		const callee = node.callee;
-		if (
-			callee.type === 'MemberExpression' &&
-			callee.property.type === 'Identifier' &&
-			callee.property.name === 'active'
-		) {
-			if (node.arguments.length !== 0) {
-				error(node, 'invalid-rune-args-length', '$effect.active', [0]);
-			}
-			return;
-		}
+	if (rune === '$effect' || rune === '$effect.pre') {
 		if (parent.type !== 'ExpressionStatement') {
 			error(node, 'invalid-effect-location');
 		}
 
 		if (node.arguments.length !== 1) {
-			error(node, 'invalid-rune-args-length', '$effect', [1]);
+			error(node, 'invalid-rune-args-length', rune, [1]);
+		}
+	}
+
+	if (rune === '$effect.active') {
+		if (node.arguments.length !== 0) {
+			error(node, 'invalid-rune-args-length', '$effect.active', [0]);
 		}
 	}
 }

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

@@ -135,7 +135,7 @@ export const javascript_visitors_runes = {
 		for (const declarator of node.declarations) {
 			const init = declarator.init;
 			const rune = get_rune(init, state.scope);
-			if (!rune || rune === '$effect') {
+			if (!rune || rune === '$effect.active') {
 				if (init != null && is_hoistable_function(init)) {
 					const hoistable_function = visit(init);
 					state.hoisted.push(
@@ -294,16 +294,11 @@ export const javascript_visitors_runes = {
 	},
 	CallExpression(node, { state, next }) {
 		const rune = get_rune(node, state.scope);
-		const callee = node.callee;
-
-		if (
-			rune === '$effect' &&
-			callee.type === 'MemberExpression' &&
-			callee.property.type === 'Identifier' &&
-			callee.property.name === 'active'
-		) {
+
+		if (rune === '$effect.active') {
 			return b.call('$.effect_active');
 		}
+
 		next();
 	}
 };

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -550,7 +550,7 @@ const javascript_visitors_runes = {
 
 		for (const declarator of node.declarations) {
 			const rune = get_rune(declarator.init, state.scope);
-			if (!rune || rune === '$effect') {
+			if (!rune || rune === '$effect.active') {
 				declarations.push(/** @type {import('estree').VariableDeclarator} */ (visit(declarator)));
 				continue;
 			}
@@ -607,16 +607,11 @@ const javascript_visitors_runes = {
 	},
 	CallExpression(node, { state, next }) {
 		const rune = get_rune(node, state.scope);
-		const callee = node.callee;
 
-		if (
-			rune === '$effect' &&
-			callee.type === 'MemberExpression' &&
-			callee.property.type === 'Identifier' &&
-			callee.property.name === 'active'
-		) {
+		if (rune === '$effect.active') {
 			return b.literal(false);
 		}
+
 		next();
 	}
 };

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

@@ -110,7 +110,7 @@ export const ElementBindings = [
 	'indeterminate'
 ];
 
-export const Runes = ['$state', '$props', '$derived', '$effect'];
+export const Runes = ['$state', '$props', '$derived', '$effect', '$effect.pre', '$effect.active'];
 
 /**
  * Whitespace inside one of these elements will not result in

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

@@ -668,15 +668,31 @@ export function set_scope(scopes) {
 
 /**
  * Returns the name of the rune if the given expression is a `CallExpression` using a rune.
- * @param {import('estree').Expression | null | undefined} node
+ * @param {import('estree').Node | null | undefined} node
  * @param {Scope} scope
  */
 export function get_rune(node, scope) {
-	const callee = get_callee_name(node);
-	if (callee === null || !Runes.includes(callee)) return null;
+	if (!node) return null;
+	if (node.type !== 'CallExpression') return null;
 
-	const binding = scope.get(callee);
+	let n = node.callee;
+
+	let joined = '';
+
+	while (n.type === 'MemberExpression') {
+		if (n.computed) return null;
+		if (n.property.type !== 'Identifier') return null;
+		joined = '.' + n.property.name + joined;
+		n = n.object;
+	}
+
+	if (n.type !== 'Identifier') return null;
+
+	joined = n.name + joined;
+	if (!Runes.includes(joined)) return null;
+
+	const binding = scope.get(n.name);
 	if (binding !== null) return null; // rune name, but references a variable or store
 
-	return callee;
+	return joined;
 }