From 076150d7b6032a3faf3d7e1dccb2bc172246244e Mon Sep 17 00:00:00 2001
From: Maximilian Krause <max@kuatsu.de>
Date: Tue, 15 Sep 2026 02:03:10 -0700
Subject: [PATCH] Preserve Platform.select initializer side effects (#1929)

Summary:

Metro replaces `Platform.select({...})` with the selected property during production transforms. JavaScript evaluates every object property initializer before calling `Platform.select`, so this can silently remove side effects from non-selected properties.

For example:

```js
Platform.select({
  ios: selected(),
  android: discarded(),
});
```

OR

```js
Platform.select({
  ios() {
    selected()
  },
  android: discarded(),
});
```

JavaScript would run both side effects, `selected()` and `discarded()`. The plugin's current behavior removes `discarded` on iOS however.

This fix preserves both side effects by testing for purity. `findProperty` also clones the selected `ObjectMethod` before calling `t.toExpression`, since `toExpression` mutates the node in place and bailing out on an impure sibling would otherwise leave the original AST mutated (e.g. `ios() {}` becoming `function () {}`), producing invalid output.

Changelog:
```
 - **[Fix]**: Preserve side effects from discarded `Platform.select` property initializers
```


Test Plan: Added regression tests, and ensured existing tests, linter and formatter pass. js1 test inline-plugin-test.js -- 64 passed. Verified the ObjectMethod bailout case emits the source unchanged instead of invalid JS.

Differential Revision: D119919582

Pulled By: vzaidman
---
 .../src/__tests__/inline-plugin-test.js       | 28 +++++++++++++++++++
 .../src/inline-plugin.js                      | 17 +++++++++--
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/packages/metro-transform-plugins/src/__tests__/inline-plugin-test.js b/packages/metro-transform-plugins/src/__tests__/inline-plugin-test.js
index fe2fb8d154..77708a5356 100644
--- a/packages/metro-transform-plugins/src/__tests__/inline-plugin-test.js
+++ b/packages/metro-transform-plugins/src/__tests__/inline-plugin-test.js
@@ -410,6 +410,34 @@ describe('inline constants', () => {
     });
   });
 
+  test('does not discard impure Platform.select initializers', () => {
+    const code = `
+      var value = Platform.select({
+        ios: selected(),
+        android: discarded(),
+      });
+    `;
+
+    compare([inlinePlugin], code, code, {
+      inlinePlatform: true,
+      platform: 'ios',
+    });
+  });
+
+  test('does not mutate ObjectMethod when bailing out on impure initializers', () => {
+    const code = `
+      var value = Platform.select({
+        ios() { return 1; },
+        android: sideEffect(),
+      });
+    `;
+
+    compare([inlinePlugin], code, code, {
+      inlinePlatform: true,
+      platform: 'ios',
+    });
+  });
+
   test('inlines Platform.select in the code when using an ObjectMethod', () => {
     const code = `
       function a() {
diff --git a/packages/metro-transform-plugins/src/inline-plugin.js b/packages/metro-transform-plugins/src/inline-plugin.js
index 4fc5dfb49d..7faf68d48b 100644
--- a/packages/metro-transform-plugins/src/inline-plugin.js
+++ b/packages/metro-transform-plugins/src/inline-plugin.js
@@ -138,7 +138,9 @@ export default function inlinePlugin(
         if (isObjectProperty(p)) {
           return p.value;
         } else if (isObjectMethod(p)) {
-          return t.toExpression(p);
+          // Clone: toExpression mutates in place, e.g. `ios() {}` would be
+          // left mutated if the purity check below bails out.
+          return t.toExpression(t.cloneNode(p));
         }
       }
     }
@@ -200,8 +202,17 @@ export default function inlinePlugin(
               findProperty(arg, 'native', () =>
                 findProperty(arg, 'default', () => t.identifier('undefined')),
               );
-
-            path.replaceWith(findProperty(arg, opts.platform, fallback));
+            const selected = findProperty(arg, opts.platform, fallback);
+
+            if (
+              arg.properties.every(
+                property =>
+                  (isObjectProperty(property) && property.value === selected) ||
+                  scope.isPure(property),
+              )
+            ) {
+              path.replaceWith(selected);
+            }
           }
         }
       },