Add more span attributes for tracing (#4)

ConditionalTasks that do not meet the conditions for execution are
opaque and hard to debug. This change adds spans attributes in both the
conditional tasks and regular tasks to make it easier to track down
issues with the graph execution.

Tasks with Absent key bindings will be attached to the spans
Conditional Tasks with failed conditionals will have their keys reported

---------

Co-authored-by: sengjea <sengjea@thoughtmachine.net>

Author: sengjea

graph.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	set "github.com/deckarep/golang-set/v2"
+	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
 	"go.opentelemetry.io/otel/trace/noop"
 	"golang.org/x/sync/errgroup"
@@ -123,6 +124,10 @@ type graphNode struct {
 	tracer          trace.Tracer
 }
 
+const (
+	traceTaskgraphAbsentKeysPrefix = "taskgraph.absent_keys."
+)
+
 // Execute the task against the binder provided in the runState.
 //
 // This assumes that all of the task's dependencies have been bound; it is the responsibility of the
@@ -169,6 +174,14 @@ func (gn *graphNode) execute(ctx context.Context, rs *runState) (err error) {
 		if !providesSet.Contains(binding.ID()) {
 			extra = append(extra, binding.ID().String())
 		}
+		if binding.Status() == Absent {
+			span.SetAttributes(
+				attribute.String(
+					traceTaskgraphAbsentKeysPrefix+binding.ID().String(),
+					fmt.Sprintf("%v", binding.Error()),
+				),
+			)
+		}
 	}
 	if len(extra) > 0 || len(missing) > 0 {
 		return wrapStackErrorf(

task.go

@@ -4,6 +4,8 @@ import (
 	"context"
 
 	set "github.com/deckarep/golang-set/v2"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/trace"
 )
 
 // A TaskSet defines a nestable collection of tasks. A Task fulfils the TaskSet interface, acting as
@@ -192,6 +194,8 @@ type Condition interface {
 	Evaluate(ctx context.Context, b Binder) (bool, error)
 	// Deps should return the IDs of the keys used by the Evaluate function.
 	Deps() []ID
+	// Keys returns the keys in the conditional
+	Keys() []ReadOnlyKey[bool]
 }
 
 // ConditionAnd evaluates to true if and only if all of the keys it contains are bound to true.
@@ -220,6 +224,11 @@ func (ca ConditionAnd) Deps() []ID {
 	return deps
 }
 
+// Keys returns the keys in the conditional
+func (ca ConditionAnd) Keys() []ReadOnlyKey[bool] {
+	return ca
+}
+
 // ConditionOr evaluates to true if any of the keys it contains are bound to true.
 type ConditionOr []ReadOnlyKey[bool]
 
@@ -246,6 +255,11 @@ func (co ConditionOr) Deps() []ID {
 	return deps
 }
 
+// Keys returns the keys in the conditional
+func (co ConditionOr) Keys() []ReadOnlyKey[bool] {
+	return co
+}
+
 // Conditional wraps tasks such that they are only run if given Condition evaluates to true. If it
 // evaluates to false, the bindings in DefaultBindings are used, with any missing keys provided by
 // the wrapped tasks bound as absent.
@@ -270,6 +284,10 @@ func (c Conditional) Locate() Conditional {
 	return c
 }
 
+const (
+	traceTaskgraphConditionalPrefix = "taskgraph.conditional."
+)
+
 // Tasks satisfies TaskSet.Tasks.
 func (c Conditional) Tasks() []Task {
 	defaultBindingsMap := map[ID]Binding{}
@@ -291,6 +309,25 @@ func (c Conditional) Tasks() []Task {
 				if err != nil {
 					return nil, err
 				}
+				span := trace.SpanFromContext(ctx)
+				span.SetAttributes(
+					attribute.Bool(traceTaskgraphConditionalPrefix+"execute", shouldExecute),
+				)
+				for _, k := range c.Condition.Keys() {
+					v, err := k.Get(b)
+					if err != nil {
+						span.SetAttributes(
+							attribute.String(
+								traceTaskgraphConditionalPrefix+k.ID().String(),
+								err.Error(),
+							),
+						)
+					} else {
+						span.SetAttributes(
+							attribute.Bool(traceTaskgraphConditionalPrefix+k.ID().String(), v),
+						)
+					}
+				}
 				if shouldExecute {
 					return t.Execute(ctx, b)
 				}