chore: remove binding.expression (#12530)

* add state.getters as alternative to binding.expression

* on second thoughts

* fix

* first of many

* couple more

* regenerate types

* more

* another

* more

* another

* another

* another

* remove binding.expression from client-side code

* tweak

* last one

* comment

* regenerate types

* add a changeset

* small tidy up

* simplify

* simplify

* simplify and fix

* simplify

Author: Rich-Harris

.changeset/four-peas-tickle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: remove internal `binding.expression` mechanism

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

@@ -65,6 +65,7 @@ export function client_component(source, analysis, options) {
 		preserve_whitespace: options.preserveWhitespace,
 		public_state: new Map(),
 		private_state: new Map(),
+		getters: {},
 		in_constructor: false,
 
 		// these are set inside the `Fragment` visitor, and cannot be used until then
@@ -583,6 +584,7 @@ export function client_module(analysis, options) {
 		legacy_reactive_statements: new Map(),
 		public_state: new Map(),
 		private_state: new Map(),
+		getters: {},
 		in_constructor: false
 	};
 

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

@@ -84,8 +84,9 @@ export function serialize_get_binding(node, state) {
 		return b.call(node);
 	}
 
-	if (binding.expression) {
-		return typeof binding.expression === 'function' ? binding.expression(node) : binding.expression;
+	if (Object.hasOwn(state.getters, node.name)) {
+		const getter = state.getters[node.name];
+		return typeof getter === 'function' ? getter(node) : getter;
 	}
 
 	if (binding.kind === 'prop' || binding.kind === 'bindable_prop') {
@@ -527,17 +528,20 @@ function get_hoistable_params(node, context) {
 				);
 			}
 
+			const expression = context.state.getters[reference];
+
 			if (
 				// If it's a destructured derived binding, then we can extract the derived signal reference and use that.
-				binding.expression !== null &&
-				typeof binding.expression !== 'function' &&
-				binding.expression.type === 'MemberExpression' &&
-				binding.expression.object.type === 'CallExpression' &&
-				binding.expression.object.callee.type === 'Identifier' &&
-				binding.expression.object.callee.name === '$.get' &&
-				binding.expression.object.arguments[0].type === 'Identifier'
+				// TODO this code is bad, we need to kill it
+				expression != null &&
+				typeof expression !== 'function' &&
+				expression.type === 'MemberExpression' &&
+				expression.object.type === 'CallExpression' &&
+				expression.object.callee.type === 'Identifier' &&
+				expression.object.callee.name === '$.get' &&
+				expression.object.arguments[0].type === 'Identifier'
 			) {
-				push_unique(b.id(binding.expression.object.arguments[0].name));
+				push_unique(b.id(expression.object.arguments[0].name));
 			} else if (
 				// If we are referencing a simple $$props value, then we need to reference the object property instead
 				(binding.kind === 'prop' || binding.kind === 'bindable_prop') &&