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Detects missing nullability annotations in Objective-C methods called from Swift, which can lead to runtime crashes via Implicitly Unwrapped Optionals.

Activate with --swift-objc-nullability.

Supported languages:

  • C/C++/ObjC: Yes
  • C#/.Net: No
  • Erlang: No
  • Hack: No
  • Java: No
  • Python: No
  • Rust: No
  • Swift: Yes

Swift/Obj-C Nullability

Reports calls from Swift code to Objective-C methods whose declaration has no _Nullable or _Nonnull annotation on a pointer return type. The Swift clang importer treats such results as Implicitly Unwrapped Optionals (T!), so any subsequent use that assumes the result is non-nil traps at runtime if the method ever returns nil. The checker raises the trap-prone call sites at compile time so the team that owns the Objective-C declaration can decide the contract explicitly.

The recommended fix lives on the MISSING_NULLABILITY_ANNOTATION issue page: annotate the Objective-C declaration with _Nullable or _Nonnull, or cast the result with as? at the Swift call site.

What is deliberately ignored​

To keep reports actionable, the checker does not report at call sites where the developer cannot or should not be asked to act:

  • Callees declared in headers under an Apple SDK or under a prebuilt framework's public-header directory: the consumer cannot edit those declarations.
  • Calls whose return value is null-checked by the Swift caller before use, e.g. if let s = api.foo() { ... }.
  • Calls whose return value is explicitly cast through an as? Optional cast, e.g. if let s = api.foo() as? NSString { ... }.

A bare force-unwrap (api.foo()!) is intentionally NOT treated as a fix — it makes the trap explicit but does not eliminate it.

List of Issue Types​

The following issue types are reported by this checker: