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name: webrtc/sdk/objc-omit-nullability-in-implementation-files description: In Objective-C NS_ASSUME_NONNULL blocks, annotate only nullable pointers and error out-parameters with _Nullable in headers, omitting redundant nonnull and implementation annotations rubric: readability severity: should_fix

Rule. In Objective-C and Objective-C++ headers enclosed by NS_ASSUME_NONNULL_BEGIN and NS_ASSUME_NONNULL_END, explicitly annotate only pointers that accept or return nil (including method parameters, return types, properties, and error out-parameters like NSError **_Nullable) with nullable or _Nullable. Do not add redundant nonnull or _Nonnull annotations within NS_ASSUME_NONNULL blocks. Additionally, omit all nullability annotations (nullable, nonnull, _Nullable, _Nonnull) from method definitions in implementation files (.m and .mm).

Why. Within NS_ASSUME_NONNULL regions, the compiler implicitly defaults all unannotated pointer types to non-null for Swift bridging and static analysis, making explicit nonnull or _Nonnull annotations redundant boilerplate. Pointers accepting or returning nil (such as optional error out-pointers) must be explicitly marked _Nullable so Swift and analyzers do not treat them as required. Repeating nullability annotations in .m or .mm implementation files is non-idiomatic, redundant with header declarations, and adds unnecessary maintenance overhead.

Examples

Bad:

// In Header.h (enclosed by NS_ASSUME_NONNULL_BEGIN)
- (nonnull RTC_OBJC_TYPE(RTCVideoEncoderCodecSupport) *)
    queryCodecSupport:(nonnull RTC_OBJC_TYPE(RTCVideoCodecInfo) *)info
      scalabilityMode:(nullable NSString *)scalabilityMode;
- (BOOL)setCodecPreferences:(NSArray<RTC_OBJC_TYPE(RTCRtpCodecCapability) *> *)codecs
                      error:(NSError **)error;

// In Implementation.mm
- (instancetype)initWithAudioDeviceModule:
    (nullable webrtc::AudioDeviceModule *)audioDeviceModule { ... }

Good:

// In Header.h (enclosed by NS_ASSUME_NONNULL_BEGIN)
- (RTC_OBJC_TYPE(RTCVideoEncoderCodecSupport) *)
    queryCodecSupport:(RTC_OBJC_TYPE(RTCVideoCodecInfo) *)info
      scalabilityMode:(nullable NSString *)scalabilityMode;
- (BOOL)setCodecPreferences:(NSArray<RTC_OBJC_TYPE(RTCRtpCodecCapability) *> *)codecs
                      error:(NSError **_Nullable)error;

// In Implementation.mm
- (instancetype)initWithAudioDeviceModule:
    (webrtc::AudioDeviceModule *)audioDeviceModule { ... }