Trait Tracer 

pub trait Tracer:
    Send
    + Sync
    + 'static {
    // Required method
    fn new_span_id(&self) -> SpanId;

    // Provided methods
    fn on_query_start(&self, _span_id: SpanId, _query: TracerQueryKey) { ... }
    fn on_cache_check(
        &self,
        _span_id: SpanId,
        _query: TracerQueryKey,
        _valid: bool,
    ) { ... }
    fn on_query_end(
        &self,
        _span_id: SpanId,
        _query: TracerQueryKey,
        _result: ExecutionResult,
    ) { ... }
    fn on_dependency_registered(
        &self,
        _span_id: SpanId,
        _parent: TracerQueryKey,
        _dependency: TracerQueryKey,
    ) { ... }
    fn on_asset_dependency_registered(
        &self,
        _span_id: SpanId,
        _parent: TracerQueryKey,
        _asset: TracerAssetKey,
    ) { ... }
    fn on_early_cutoff_check(
        &self,
        _span_id: SpanId,
        _query: TracerQueryKey,
        _output_changed: bool,
    ) { ... }
    fn on_asset_requested(
        &self,
        _asset: TracerAssetKey,
        _state: TracerAssetState,
    ) { ... }
    fn on_asset_resolved(&self, _asset: TracerAssetKey, _changed: bool) { ... }
    fn on_asset_invalidated(&self, _asset: TracerAssetKey) { ... }
    fn on_query_invalidated(
        &self,
        _query: TracerQueryKey,
        _reason: InvalidationReason,
    ) { ... }
    fn on_cycle_detected(&self, _path: Vec<TracerQueryKey>) { ... }
    fn on_missing_dependency(
        &self,
        _query: TracerQueryKey,
        _dependency_description: String,
    ) { ... }
}

Tracer trait for observing query-flow execution.

Implementations can collect events for testing, forward to the tracing crate, or provide custom observability.

All methods have default empty implementations, so you only need to override the events you’re interested in. The NoopTracer uses all defaults for zero-cost when tracing is disabled.

Thread Safety

Implementations must be Send + Sync as the tracer may be called from multiple threads concurrently.

Required Methods

fn new_span_id(&self) -> SpanId

Generate a new unique span ID.

This is the only required method. Called at the start of each query execution.

Provided Methods

fn on_query_start(&self, _span_id: SpanId, _query: TracerQueryKey)

Called when a query execution starts.

fn on_cache_check(&self, _span_id: SpanId, _query: TracerQueryKey, _valid: bool)

Called when cache validity is checked.

fn on_query_end( &self, _span_id: SpanId, _query: TracerQueryKey, _result: ExecutionResult, )

Called when a query execution ends.

fn on_dependency_registered( &self, _span_id: SpanId, _parent: TracerQueryKey, _dependency: TracerQueryKey, )

Called when a query dependency is registered during execution.

fn on_asset_dependency_registered( &self, _span_id: SpanId, _parent: TracerQueryKey, _asset: TracerAssetKey, )

Called when an asset dependency is registered during execution.

fn on_early_cutoff_check( &self, _span_id: SpanId, _query: TracerQueryKey, _output_changed: bool, )

Called when early cutoff comparison is performed.

fn on_asset_requested(&self, _asset: TracerAssetKey, _state: TracerAssetState)

Called when an asset is requested.

fn on_asset_resolved(&self, _asset: TracerAssetKey, _changed: bool)

Called when an asset is resolved with a value.

fn on_asset_invalidated(&self, _asset: TracerAssetKey)

Called when an asset is invalidated.

fn on_query_invalidated( &self, _query: TracerQueryKey, _reason: InvalidationReason, )

Called when a query is invalidated.

fn on_cycle_detected(&self, _path: Vec<TracerQueryKey>)

Called when a dependency cycle is detected.

fn on_missing_dependency( &self, _query: TracerQueryKey, _dependency_description: String, )

Called when a missing dependency error occurs.

Implementors

impl Tracer for NoopTracer