enable expo experimental tree shaking

Dockerfile

@@ -17,6 +17,10 @@ ENV CI=1
 # use the pnpm version specified in package.json
 ENV pnpm_config_pm_on_fail=download
 
+# Metro's web export needs far more heap than Node's default (~1GB in the
+# container), which crashes the bundle step with a V8 OOM.
+ENV NODE_OPTIONS="--max-old-space-size=8192"
+
 # The latest git hash of the preview branch on render.com
 # https://render.com/docs/docker-secrets#environment-variables-in-docker-builds
 ARG RENDER_GIT_COMMIT

babel.config.js

@@ -1,3 +1,24 @@
+/**
+ * React Compiler tags generated nodes with loc = Symbol(GeneratedSource),
+ * which breaks the structuredClone Metro performs on the AST when
+ * EXPO_UNSTABLE_TREE_SHAKING is enabled. Strip them after all other
+ * transforms have run.
+ */
+const stripSymbolLocs = () => ({
+  post(file) {
+    file.path.traverse({
+      enter(path) {
+        if (typeof path.node.loc === 'symbol') {
+          path.node.loc = undefined
+        }
+      },
+    })
+    if (typeof file.ast.program.loc === 'symbol') {
+      file.ast.program.loc = undefined
+    }
+  },
+})
+
 /**
  * @param {import("@babel/core").ConfigAPI} api
  * @returns {import("@babel/core").InputOptions}
@@ -45,6 +66,7 @@ module.exports = function (api) {
         : []),
       ...(api.env('production') ? ['transform-remove-console'] : []),
 
+      stripSymbolLocs,
       'react-native-worklets/plugin', // NOTE: this plugin MUST be last
     ],
   }

package.json

@@ -47,7 +47,7 @@
     "web": "expo start --web",
     "use-build-number": "./scripts/useBuildNumberEnv.sh",
     "use-build-number-with-bump": "./scripts/useBuildNumberEnvWithBump.sh",
-    "build-web": "expo export --platform web --source-maps && node ./scripts/post-web-build.js",
+    "build-web": "EXPO_UNSTABLE_METRO_OPTIMIZE_GRAPH=1 EXPO_UNSTABLE_TREE_SHAKING=1 expo export --platform web --source-maps && node ./scripts/post-web-build.js",
     "build-all": "pnpm intl:build && pnpm use-build-number-with-bump eas build --platform all",
     "build-ios": "pnpm use-build-number-with-bump eas build -p ios",
     "build-android": "pnpm use-build-number-with-bump eas build -p android",