fix: avoid chaining multiple atlas serializers together

src/index.ts

@@ -8,3 +8,4 @@ export { AtlasError, AtlasValidationError } from './utils/errors';
 export { createAtlasMiddleware } from './utils/middleware';
 export { fuzzyFilterModules } from './utils/search';
 export { createStatsFile, validateStatsFile, getStatsMetdata, getStatsPath } from './utils/stats';
+export { attachMetroSerializer } from './utils/metro';

src/metro.ts

@@ -2,6 +2,7 @@ import { type MetroConfig } from 'metro-config';
 
 import { convertGraph } from './data/MetroGraphSource';
 import { writeStatsEntry } from './data/StatsFileSource';
+import { attachMetroSerializer } from './utils/metro';
 import { createStatsFile, getStatsPath } from './utils/stats';
 
 type ExpoAtlasOptions = Partial<{
@@ -27,7 +28,6 @@ type ExpoAtlasOptions = Partial<{
  */
 export function withExpoAtlas(config: MetroConfig, options: ExpoAtlasOptions = {}) {
   const projectRoot = config.projectRoot;
-  const originalSerializer = config.serializer?.customSerializer ?? (() => {});
 
   if (!projectRoot) {
     throw new Error('No "projectRoot" configured in Metro config.');
@@ -42,16 +42,13 @@ export function withExpoAtlas(config: MetroConfig, options: ExpoAtlasOptions = {
   // Note(cedric): we don't have to await this, Metro would never bundle before this is finisheds
   createStatsFile(statsFile);
 
-  // @ts-expect-error
-  config.serializer.customSerializer = (entryPoint, preModules, graph, options) => {
+  attachMetroSerializer(config, (entryPoint, preModules, graph, options) => {
     // Note(cedric): we don't have to await this, it has a built-in write queue
     writeStatsEntry(
       statsFile,
       convertGraph({ projectRoot, entryPoint, preModules, graph, options, extensions })
     );
-
-    return originalSerializer(entryPoint, preModules, graph, options);
-  };
+  });
 
   return config;
 }

src/utils/metro.ts

@@ -0,0 +1,36 @@
+import type { ConfigT as MetroConfig, InputConfigT as MetroInputConfig } from 'metro-config';
+
+const atlasSerializerSymbol = Symbol('expo-atlas-serializer');
+const originalSerializerSymbol = Symbol('expo-atlas-original-serializer');
+
+type MetroSerializerParams = Parameters<NonNullable<MetroConfig['serializer']['customSerializer']>>
+type AtlasSerializer = (...params: MetroSerializerParams) => void;
+
+/**
+ * Attach a custom serializer, marked as being an Expo Atlas serializer.
+ * If there was a previous serializer, it will be overwritten to avoid conflicts.
+ */
+export function attachMetroSerializer(
+  config: MetroConfig | MetroInputConfig,
+  serializer: AtlasSerializer
+) {
+  // @ts-expect-error
+  if (!config.serializer) config.serializer = {};
+
+  let prevSerializer = config.serializer?.customSerializer;
+
+  // Already attached, overwrite the serializer
+  if (prevSerializer?.[atlasSerializerSymbol]) {
+    prevSerializer = prevSerializer[originalSerializerSymbol];
+  }
+
+  // @ts-expect-error
+  config.serializer.customSerializer = (entryPoint, preModules, graph, options) => {
+    serializer(entryPoint, preModules, graph, options);
+    return prevSerializer?.(entryPoint, preModules, graph, options);
+  };
+
+  // Mark this serializer as being atlas
+  config.serializer.customSerializer![atlasSerializerSymbol] = true;
+  config.serializer.customSerializer![originalSerializerSymbol] = prevSerializer;
+}