Replace recordingSpan attributes implementation with slice of attribu…

…tes (#2576)

* Replace recordingSpan attributes implementation

Instead of an LRU strategy for cap-ing span attributes, comply with the
specification and drop last added. To do this, the attributesmap is
replaced with a slice of attributes.

* Remove attributesmap files

* Refine addition algorithm

Unify duplicated code.

Fix deduplication algorithm.

Fix droppedAttributes to always be returned, even if the span has no
attributes.

* Unify span SetAttributes tests

* Doc fix to attr drop order in changelog

* Test span and snapshot attrs

* fix lint

* Add tests for recordingSpan method defaults

* Comment why pre-allocation is not done

* Correct grammar in recordingSpan allocation comment

* Update sdk/trace/tracer.go

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

CHANGELOG.md

@@ -31,6 +31,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Specify explicit buckets in Prometheus example. (#2493)
 - W3C baggage will now decode urlescaped values. (#2529)
 - Baggage members are now only validated once, when calling `NewMember` and not also when adding it to the baggage itself. (#2522)
+- The order attributes are dropped from spans in the `go.opentelemetry.io/otel/sdk/trace` package when capacity is reached is fixed to be in compliance with the OpenTelemetry specification.
+  Instead of dropping the least-recently-used attribute, the last added attribute is dropped.
+  This drop order still only applies to attributes with unique keys not already contained in the span.
+  If an attribute is added with a key already contained in the span, that attribute is updated to the new value being added. (#2576)
 
 ### Removed
 

sdk/trace/benchmark_test.go

@@ -16,6 +16,7 @@ package trace_test
 
 import (
 	"context"
+	"fmt"
 	"testing"
 	"time"
 
@@ -24,6 +25,28 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
+func BenchmarkSpanSetAttributesOverCapacity(b *testing.B) {
+	tp := sdktrace.NewTracerProvider(
+		sdktrace.WithSpanLimits(sdktrace.SpanLimits{AttributeCountLimit: 1}),
+	)
+	tracer := tp.Tracer("BenchmarkSpanSetAttributesOverCapacity")
+	ctx := context.Background()
+	attrs := make([]attribute.KeyValue, 128)
+	for i := range attrs {
+		key := fmt.Sprintf("key-%d", i)
+		attrs[i] = attribute.Bool(key, true)
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		_, span := tracer.Start(ctx, "/foo")
+		span.SetAttributes(attrs...)
+		span.End()
+	}
+}
+
 func BenchmarkStartEndSpan(b *testing.B) {
 	traceBenchmark(b, "Benchmark StartEndSpan", func(b *testing.B, t trace.Tracer) {
 		ctx := context.Background()