From 40478befe06126b867565dc4e84d23760fb2af57 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20Paj=C4=85k?= <pellared@hotmail.com>
Date: Mon, 11 Mar 2024 12:52:27 +0100
Subject: [PATCH 1/4] Add zero alloc tests to TestSpanFromContext

---
 trace/context_test.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/trace/context_test.go b/trace/context_test.go
index d9378e1c430..828338259f4 100644
--- a/trace/context_test.go
+++ b/trace/context_test.go
@@ -77,6 +77,16 @@ func TestSpanFromContext(t *testing.T) {
 			// Ensure SpanContextFromContext is just
 			// SpanFromContext(…).SpanContext().
 			assert.Equal(t, tc.expectedSpan.SpanContext(), SpanContextFromContext(tc.context))
+
+			// Check that SpanFromContext does not produce any heap allocation.
+			assert.Equal(t, 0.0, testing.AllocsPerRun(5, func() {
+				SpanFromContext(tc.context)
+			}), "SpanFromContext allocs")
+
+			// Check that SpanContextFromContext does not produce any heap allocation.
+			assert.Equal(t, 0.0, testing.AllocsPerRun(5, func() {
+				SpanContextFromContext(tc.context)
+			}), "SpanFromContext allocs")
 		})
 	}
 }

From d2b832b5b00b228f5e803eee759848bae2cb6ffb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20Paj=C4=85k?= <pellared@hotmail.com>
Date: Mon, 11 Mar 2024 12:53:14 +0100
Subject: [PATCH 2/4] trace: SpanFromContext has no allocs

---
 trace/context.go | 4 ++--
 trace/noop.go    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/trace/context.go b/trace/context.go
index 5074bb44557..5650a174b4a 100644
--- a/trace/context.go
+++ b/trace/context.go
@@ -36,12 +36,12 @@ func ContextWithRemoteSpanContext(parent context.Context, rsc SpanContext) conte
 // performs no operations is returned.
 func SpanFromContext(ctx context.Context) Span {
 	if ctx == nil {
-		return noopSpan{}
+		return noopSpanInstance
 	}
 	if span, ok := ctx.Value(currentSpanKey).(Span); ok {
 		return span
 	}
-	return noopSpan{}
+	return noopSpanInstance
 }
 
 // SpanContextFromContext returns the current Span's SpanContext.
diff --git a/trace/noop.go b/trace/noop.go
index 583f109b064..84c775492ba 100644
--- a/trace/noop.go
+++ b/trace/noop.go
@@ -41,7 +41,7 @@ func (t noopTracer) Start(ctx context.Context, name string, _ ...SpanStartOption
 	span := SpanFromContext(ctx)
 	if _, ok := span.(nonRecordingSpan); !ok {
 		// span is likely already a noopSpan, but let's be sure
-		span = noopSpan{}
+		span = noopSpanInstance
 	}
 	return ContextWithSpan(ctx, span), span
 }
@@ -49,7 +49,7 @@ func (t noopTracer) Start(ctx context.Context, name string, _ ...SpanStartOption
 // noopSpan is an implementation of Span that performs no operations.
 type noopSpan struct{ embedded.Span }
 
-var _ Span = noopSpan{}
+var noopSpanInstance Span = noopSpan{}
 
 // SpanContext returns an empty span context.
 func (noopSpan) SpanContext() SpanContext { return SpanContext{} }

From 3a2dfbfc6cd576284e2956c37b43628eb6f36dab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20Paj=C4=85k?= <pellared@hotmail.com>
Date: Mon, 11 Mar 2024 12:56:19 +0100
Subject: [PATCH 3/4] Fix assertion failure name

---
 trace/context_test.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/trace/context_test.go b/trace/context_test.go
index 828338259f4..38deb0aee5f 100644
--- a/trace/context_test.go
+++ b/trace/context_test.go
@@ -86,7 +86,7 @@ func TestSpanFromContext(t *testing.T) {
 			// Check that SpanContextFromContext does not produce any heap allocation.
 			assert.Equal(t, 0.0, testing.AllocsPerRun(5, func() {
 				SpanContextFromContext(tc.context)
-			}), "SpanFromContext allocs")
+			}), "SpanContextFromContext allocs")
 		})
 	}
 }

From 447dd29a1e2f49c7e4d9304e14d0ffd3150d751e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20Paj=C4=85k?= <pellared@hotmail.com>
Date: Mon, 11 Mar 2024 13:00:52 +0100
Subject: [PATCH 4/4] Update changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04b1d584de0..1f23df31399 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Changed
+
+- `SpanFromContext` and `SpanContextFromContext` in `go.opentelemetry.io/otel/trace` no longer make a heap allocation when the passed context has no span. (#5049)
+
 ### Fixed
 
 - Clarify the documentation about equivalence guarantees for the `Set` and `Distinct` types in `go.opentelemetry.io/otel/attribute`. (#5027)