add SetAttribute(string,interface{}) (#674)

api/trace/api.go

@@ -121,6 +121,9 @@ type Span interface {
 
 	// Set span attributes
 	SetAttributes(...core.KeyValue)
+
+	// Set singular span attribute, with type inference.
+	SetAttribute(string, interface{})
 }
 
 // StartOption applies changes to StartConfig that sets options at span start time.

api/trace/context_test.go

@@ -97,6 +97,10 @@ func (mockSpan) SetError(v bool) {
 func (mockSpan) SetAttributes(attributes ...core.KeyValue) {
 }
 
+// SetAttribute does nothing.
+func (mockSpan) SetAttribute(k string, v interface{}) {
+}
+
 // End does nothing.
 func (mockSpan) End(options ...trace.EndOption) {
 }

api/trace/noop_span.go

@@ -50,6 +50,10 @@ func (NoopSpan) SetError(v bool) {
 func (NoopSpan) SetAttributes(attributes ...core.KeyValue) {
 }
 
+// SetAttribute does nothing.
+func (NoopSpan) SetAttribute(k string, v interface{}) {
+}
+
 // End does nothing.
 func (NoopSpan) End(options ...EndOption) {
 }

api/trace/testtrace/span.go

@@ -24,6 +24,7 @@ import (
 	"google.golang.org/grpc/codes"
 
 	"go.opentelemetry.io/otel/api/core"
+	"go.opentelemetry.io/otel/api/key"
 	"go.opentelemetry.io/otel/api/trace"
 )
 
@@ -177,6 +178,10 @@ func (s *Span) SetAttributes(attrs ...core.KeyValue) {
 	}
 }
 
+func (s *Span) SetAttribute(k string, v interface{}) {
+	s.SetAttributes(key.Infer(k, v))
+}
+
 // Name returns the name most recently set on the Span, either at or after creation time.
 // It cannot be change after End has been called on the Span.
 func (s *Span) Name() string {

bridge/opentracing/internal/mock.go

@@ -239,6 +239,10 @@ func (s *MockSpan) SetAttributes(attributes ...otelcore.KeyValue) {
 	})
 }
 
+func (s *MockSpan) SetAttribute(k string, v interface{}) {
+	s.SetAttributes(otelkey.Infer(k, v))
+}
+
 func (s *MockSpan) applyUpdate(update otelcorrelation.MapUpdate) {
 	s.Attributes = s.Attributes.Apply(update)
 }

internal/trace/mock_span.go

@@ -59,6 +59,10 @@ func (ms *MockSpan) SetError(v bool) {
 func (ms *MockSpan) SetAttributes(attributes ...core.KeyValue) {
 }
 
+// SetAttribute does nothing.
+func (ms *MockSpan) SetAttribute(k string, v interface{}) {
+}
+
 // End does nothing.
 func (ms *MockSpan) End(options ...apitrace.EndOption) {
 }

sdk/trace/span.go

@@ -24,6 +24,7 @@ import (
 	"google.golang.org/grpc/codes"
 
 	"go.opentelemetry.io/otel/api/core"
+	"go.opentelemetry.io/otel/api/key"
 	apitrace "go.opentelemetry.io/otel/api/trace"
 	export "go.opentelemetry.io/otel/sdk/export/trace"
 	"go.opentelemetry.io/otel/sdk/internal"
@@ -100,6 +101,10 @@ func (s *span) SetAttributes(attributes ...core.KeyValue) {
 	s.copyToCappedAttributes(attributes...)
 }
 
+func (s *span) SetAttribute(k string, v interface{}) {
+	s.SetAttributes(key.Infer(k, v))
+}
+
 func (s *span) End(options ...apitrace.EndOption) {
 	if s == nil {
 		return