yup-review

YUP Audio Plugin Review

YUP looks JUCE-like in places, but its plugin API has its own parameter handles, bus layout, editor contract, and wrapper behavior. Review those directly instead of applying APVTS rules.

Step 0 - Run universal checks first

Invoke audio-dsp-review and audio-numerics-review before this skill. This skill adds YUP-specific checks on top; it does not replace realtime-safety or numerics reviews.

Step 1 - Identify plugin structure

Locate the core classes and boundaries:

• yup::AudioProcessor - audio thread owns processBlock; wrapper/host code calls lifecycle, state, and preset methods
• yup::AudioProcessorEditor - UI/message thread only; never call from audio thread
• yup::AudioParameter - atomic scalar value plus listeners for host/UI notification
• yup::AudioParameterHandle - audio-thread smoothing/read path; initialise in prepareToPlay
• yup::AudioBusLayout - immutable I/O contract exposed to plugin wrappers
• extern "C" yup::AudioProcessor* createPluginProcessor() - plugin entry point used by wrappers

Step 2 - Scan for YUP violations

| Violation | Where to look | Risk | |-----------|--------------|------| | AudioParameterHandle default-constructed and used before prepareToPlay | Members and processBlock | Null parameter assertion/crash; wrong smoothing state | | Missing handle.updateNextAudioBlock() | processBlock | Automation and smoothing lag or never update | | Recreating AudioParameterHandle in processBlock | Audio callback | Reinitialises smoothing and may add avoidable work/glitches | | setValueNotifyingHost(), beginChangeGesture(), or endChangeGesture() from audio code | processBlock, MIDI handlers, DSP helpers | Listener/host notification path is not a realtime data path | | Allocating voices, buffers, MemoryBlock, String, std::vector, or smart-pointer objects in processBlock | MIDI note-on, scratch buffers, metering | Heap traffic causes xruns | | YUP_DBG, Logger::writeToLog, File, URL, JSON/XML, or string formatting in audio code | Debug and error paths | Logging/I/O/allocation on audio thread | | Hard-coded channel pointers without layout checks | getWritePointer(0/1) and bus setup | Mono, sidechain, or unusual host layout crashes/corrupts audio | | Mutating MidiBuffer while iterating it | MIDI loops | Iterator invalidation or unbounded allocation | | prepareToPlay not resetting all DSP and note state | Lifecycle methods | Host reactivation leaves stale filter history, held notes, or ramps | | flush() missing for synths/effects with tails or voices | CLAP reset handling | Host reset leaves hanging notes or stale delay/reverb tails | | State load/save left unimplemented | loadStateFromMemory, saveStateIntoMemory | DAW session recall and presets fail | | Long work under getProcessLock() or state swaps with no handoff | UI/state/background code | Processing may skip under CLAP try-lock or race under other wrappers | | Editor stores raw processor-owned UI pointers or processor stores editor pointer | Editor/processor members | Dangling pointer when host closes editor |

Step 3 - Check YUP API contracts

• Constructor: parameters are added once; IDs are unique and stable; bus layout matches PLUGIN_IS_SYNTH / PLUGIN_IS_MONO intent.
• prepareToPlay: allocates and resets all state; constructs handles with current sample rate; tolerates repeated calls.
• processBlock: reads smoothed parameters through handles; respects audioBuffer.getNumSamples() and actual channel count; clears or writes every output sample it owns.
• MIDI: consumes events in sample order; uses bounded voice/event storage; clears or rewrites outgoing MIDI deliberately.
• Editor: uses gesture begin/end around drags; calls setValueNotifyingHost() for user changes; polls parameter values with a timer using dontSendNotification.
• State/presets: serialises all host-visible parameters and preset data; validates memory before applying; does not assume state callbacks are the audio thread.
• Format wrappers: CLAP and VST3 builds are enabled only as needed; CLAP/VST3/standalone targets all link the same ${target_name}_shared code.

Step 4 - Write the review

## YUP Plugin Review: `[file / class]`

### Verdict
[Safe | Has critical violations | Warnings only] - [one sentence summary]

### Critical Violations
**[Category]: [description]**
`file:line` - `offending code`
Why: [one sentence on YUP lifecycle/thread/API risk]
Fix: [concrete YUP-idiomatic suggestion]

### Warnings
[same format]

### What's Done Well
[correct patterns observed]

### Recommended Fixes (priority order)
1. ...

Quick fix table

| Violation | Fix | |-----------|-----| | Direct unsmoothed parameter read for DSP | Keep AudioParameter::Ptr, initialise AudioParameterHandle in prepareToPlay, read via the handle | | Missing gesture pairing | Call beginChangeGesture() on drag start and endChangeGesture() on drag end | | UI value changes with setValue() | Use setValueNotifyingHost() for user edits so automation/host state is notified | | Allocating voices on note-on | Preallocate voice slots and reuse them; reject/steal voices when full | | Hard-coded stereo | Declare stereo in AudioBusLayout and guard getNumChannels() before channel access | | Missing reset | Clear voices, delay lines, filters, smoothers, and pending MIDI in both prepareToPlay and flush() where relevant | | Unimplemented state recall | Serialise parameters and presets into MemoryBlock; validate and apply from non-audio state callbacks | | Audio-to-UI updates | Write scalars to atomics or a preallocated lock-free queue; have editor Timer poll them |

For full code examples and YUP-specific BAD/GOOD patterns, see references/yup-violations.md.