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name: webrtc/avoid-default-arguments-when-adding-parameters description: When adding configuration parameters, avoid default arguments on internal functions to enforce explicit call-site updates, but default temporary rollout flags with cleanup TODOs rubric: readability severity: blocking

Rule. When introducing new configuration flags, modes, or parameters to constructors and internal functions, avoid assigning default argument values so that all call sites, platform branches, and factory methods are explicitly updated and reviewed at compile time. Conversely, when adding temporary rollout flags or optional parameters to existing shared methods or factory functions to prevent breaking callers during rollout, provide a default argument value accompanied by an attributed cleanup TODO tracking its removal.

Why. Omitting default values on internal APIs ensures the compiler catches all call sites that need intentional configuration updates. For temporary rollout flags in shared code, providing a default value avoids breaking external or downstream consumers during incremental rollout, while a cleanup TODO prevents permanent API clutter.

Examples

Bad:

// Bad: Default argument on internal constructor masks call sites that should be updated.
FullScreenWindowDetector(
    ApplicationHandlerFactory application_handler_factory,
    bool use_heuristic_fullscreen_powerpoint_windows = true);

// Bad: Mandatory rollout parameter on shared factory breaks all existing callers without notice.
static std::unique_ptr<RtpPacketizer> Create(
    absl::optional<VideoCodecType> type,
    rtc::ArrayView<const uint8_t> payload,
    PayloadSizeLimits limits,
    const RTPVideoHeader& rtp_video_header,
    bool enable_av1_even_split);

Good:

// Good: Explicit parameter forces compiler errors at all call sites across platforms.
FullScreenWindowDetector(
    ApplicationHandlerFactory application_handler_factory,
    bool use_heuristic_fullscreen_powerpoint_windows);

// Good: Default value with cleanup TODO preserves call-site compatibility during rollout.
static std::unique_ptr<RtpPacketizer> Create(
    absl::optional<VideoCodecType> type,
    rtc::ArrayView<const uint8_t> payload,
    PayloadSizeLimits limits,
    const RTPVideoHeader& rtp_video_header,
    // TODO(bugs.webrtc.org/15927): remove after rollout.
    bool enable_av1_even_split = false);