alternative HMR update fix

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

@@ -418,7 +418,13 @@ export function client_component(source, analysis, options) {
 
 	if (options.hmr) {
 		const accept_fn_body = [
-			b.stmt(b.call('$.set', b.id('s'), b.member(b.id('module.default'), b.id('$.ORIGINAL'), true)))
+			b.stmt(
+				b.call(
+					'$.set',
+					b.id('import.meta.hot.data.source'),
+					b.member(b.id('module.default'), b.id('$.ORIGINAL'), true)
+				)
+			)
 		];
 
 		if (analysis.css.hash) {
@@ -438,13 +444,27 @@ export function client_component(source, analysis, options) {
 		}
 
 		const hmr = b.block([
-			b.const(b.id('s'), b.call('$.source', b.id(analysis.name))),
-			b.const(b.id('filename'), b.member(b.id(analysis.name), b.id('filename'))),
+			b.stmt(
+				b.assignment(
+					'??=',
+					b.id('import.meta.hot.data.source'),
+					b.call('$.source', b.id(analysis.name))
+				)
+			),
+			b.const(b.id('$$filename'), b.member(b.id(analysis.name), b.id('$.FILENAME'), true)),
 			b.const(b.id('$$original'), b.id(analysis.name)),
-			b.stmt(b.assignment('=', b.id(analysis.name), b.call('$.hmr', b.id('s')))),
-			b.stmt(b.assignment('=', b.member(b.id(analysis.name), b.id('filename')), b.id('filename'))),
+			b.stmt(
+				b.assignment('=', b.id(analysis.name), b.call('$.hmr', b.id('import.meta.hot.data.source')))
+			),
+			b.stmt(
+				b.assignment(
+					'=',
+					b.member(b.id(analysis.name), b.id('$.FILENAME'), true),
+					b.id('$$filename')
+				)
+			),
 			// Assign the original component to the wrapper so we can use it on hot reload patching,
-			// else we would call the HMR function two times
+			// else we would create a matryoshka doll of HMR wrappers
 			b.stmt(
 				b.assignment(
 					'=',

packages/svelte/tests/snapshot/samples/hmr/_expected/client/index.svelte.js

@@ -10,16 +10,17 @@ function Hmr($$anchor) {
 }
 
 if (import.meta.hot) {
-	const s = $.source(Hmr);
-	const filename = Hmr.filename;
+	import.meta.hot.data.source ??= $.source(Hmr);
+
+	const $$filename = Hmr[$.FILENAME];
 	const $$original = Hmr;
 
-	Hmr = $.hmr(s);
-	Hmr.filename = filename;
+	Hmr = $.hmr(import.meta.hot.data.source);
+	Hmr[$.FILENAME] = $$filename;
 	Hmr[$.ORIGINAL] = $$original;
 
 	import.meta.hot.accept((module) => {
-		$.set(s, module.default[$.ORIGINAL]);
+		$.set(import.meta.hot.data.source, module.default[$.ORIGINAL]);
 	});
 }