React Native "duplicate symbol(s)" (iOS link) in CI

ld requires each symbol to be defined once. "duplicate symbol ... for architecture arm64" means two linked objects define the same symbol: a pod linked both statically and dynamically, a library included twice, or a transitive duplicate.

What this error means

The link step fails with "duplicate symbol '_X' in: ...a.o ...b.o" and "ld: N duplicate symbols for architecture arm64".

duplicate symbol '_OBJC_CLASS_$_RCTView' in:
    .../libReactCommon.a(RCTView.o)
    .../libReact-Core.a(RCTView.o)
ld: 1 duplicate symbol for architecture arm64

Common causes

A library linked more than once

A pod is pulled in by two paths (static and dynamic, or duplicated entries), so its symbols are defined twice.

use_frameworks mode mismatch

Switching between static and dynamic frameworks without a clean reinstall leaves both copies linked.

How to fix it

Clean and reinstall pods consistently

Remove Pods and Podfile.lock, then pod install fresh.
Pick one linkage mode (static or use_frameworks!) and keep it.
Rebuild after a clean.

Terminal

cd ios && rm -rf Pods Podfile.lock && pod install

Remove the duplicate dependency entry

Ensure the pod or library is declared once and not also linked manually in the target.

How to prevent it

Use a single, consistent framework linkage mode.
Avoid declaring a pod and also linking it manually.
Do a clean pod install after changing use_frameworks settings.