add state.getters as alternative to binding.expression

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: new Map(),
 		in_constructor: false,
 
 		// these are set inside the `Fragment` visitor, and cannot be used until then
@@ -582,6 +583,7 @@ export function client_module(analysis, options) {
 		legacy_reactive_statements: new Map(),
 		public_state: new Map(),
 		private_state: new Map(),
+		getters: new Map(),
 		in_constructor: false
 	};
 

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

@@ -84,6 +84,11 @@ export function serialize_get_binding(node, state) {
 		return b.call(node);
 	}
 
+	const getter = state.getters.get(binding);
+	if (getter) {
+		return typeof getter === 'function' ? getter(node) : getter;
+	}
+
 	if (binding.expression) {
 		return typeof binding.expression === 'function' ? binding.expression(node) : binding.expression;
 	}

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

@@ -221,6 +221,11 @@ function serialize_get_binding(node, state) {
 		);
 	}
 
+	const getter = state.getters.get(binding);
+	if (getter) {
+		return typeof getter === 'function' ? getter(node) : getter;
+	}
+
 	if (binding.expression) {
 		return typeof binding.expression === 'function' ? binding.expression(node) : binding.expression;
 	}
@@ -1983,6 +1988,7 @@ export function server_component(analysis, options) {
 		namespace: options.namespace,
 		preserve_whitespace: options.preserveWhitespace,
 		private_derived: new Map(),
+		getters: new Map(),
 		skip_hydration_boundaries: false
 	};
 
@@ -2293,7 +2299,8 @@ export function server_module(analysis, options) {
 		// to be present for `javascript_visitors_legacy` and so is included in module
 		// transform state as well as component transform state
 		legacy_reactive_statements: new Map(),
-		private_derived: new Map()
+		private_derived: new Map(),
+		getters: new Map()
 	};
 
 	const module = /** @type {import('estree').Program} */ (

packages/svelte/src/compiler/phases/3-transform/types.d.ts

@@ -1,10 +1,12 @@
 import type { Scope } from '../scope.js';
-import type { SvelteNode, ValidatedModuleCompileOptions } from '#compiler';
+import type { Binding, SvelteNode, ValidatedModuleCompileOptions } from '#compiler';
 import type { Analysis } from '../types.js';
+import type { Expression, Identifier } from 'estree';
 
 export interface TransformState {
 	readonly analysis: Analysis;
 	readonly options: ValidatedModuleCompileOptions;
 	readonly scope: Scope;
 	readonly scopes: Map<SvelteNode, Scope>;
+	readonly getters: Map<Binding, Expression | ((id: Identifier) => Expression)>;
 }

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

@@ -308,6 +308,7 @@ export interface Binding {
 	/**
 	 * If this is set, all references should use this expression instead of the identifier name.
 	 * If a function is given, it will be called with the identifier at that location and should return the new expression.
+	 * @deprecated use `state.getters.get(binding)` instead
 	 */
 	expression: Expression | ((id: Identifier) => Expression) | null;
 	/** If this is set, all mutations should use this expression */