feat(stdouttrace): generate counter implementation via templates (#7231)

Use templates to generate the counter implementation for `stdouttrace`,
so it can be easily reused in other modules.

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

exporters/stdout/stdouttrace/internal/counter/counter.go

@@ -1,3 +1,6 @@
+// Code generated by gotmpl. DO NOT MODIFY.
+// source: internal/shared/counter/counter.go.tmpl
+
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 

exporters/stdout/stdouttrace/internal/counter/counter_test.go

@@ -1,3 +1,6 @@
+// Code generated by gotmpl. DO NOT MODIFY.
+// source: internal/shared/counter/counter_test.go.tmpl
+
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
@@ -59,4 +62,4 @@ func TestNextExporterIDConcurrentSafe(t *testing.T) {
 	if id := NextExporterID(); id != expected {
 		t.Errorf("NextExporterID() = %d; want %d", id, expected)
 	}
-}
+}

exporters/stdout/stdouttrace/internal/gen.go

@@ -0,0 +1,9 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package internal provides internal functionality for the stdouttrace
+// package.
+package internal // import "go.opentelemetry.io/otel/exporters/stdout/stdouttrace/internal"
+
+//go:generate gotmpl --body=../../../../internal/shared/counter/counter.go.tmpl "--data={}" --out=counter/counter.go
+//go:generate gotmpl --body=../../../../internal/shared/counter/counter_test.go.tmpl "--data={}" --out=counter/counter_test.go

internal/shared/counter/counter.go.tmpl

@@ -0,0 +1,31 @@
+// Code generated by gotmpl. DO NOT MODIFY.
+// source: internal/shared/counter/counter.go.tmpl
+
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package counter provides a simple counter for generating unique IDs.
+//
+// This package is used to generate unique IDs while allowing testing packages
+// to reset the counter.
+package counter // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc/internal/counter"
+
+import "sync/atomic"
+
+// exporterN is a global 0-based count of the number of exporters created.
+var exporterN atomic.Int64
+
+// NextExporterID returns the next unique ID for an exporter.
+func NextExporterID() int64 {
+	const inc = 1
+	return exporterN.Add(inc) - inc
+}
+
+// SetExporterID sets the exporter ID counter to v and returns the previous
+// value.
+//
+// This function is useful for testing purposes, allowing you to reset the
+// counter. It should not be used in production code.
+func SetExporterID(v int64) int64 {
+	return exporterN.Swap(v)
+}

internal/shared/counter/counter_test.go.tmpl

@@ -0,0 +1,65 @@
+// Code generated by gotmpl. DO NOT MODIFY.
+// source: internal/shared/counter/counter_test.go.tmpl
+
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package counter
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestNextExporterID(t *testing.T) {
+	SetExporterID(0)
+
+	var expected int64
+	for range 10 {
+		id := NextExporterID()
+		if id != expected {
+			t.Errorf("NextExporterID() = %d; want %d", id, expected)
+		}
+		expected++
+	}
+}
+
+func TestSetExporterID(t *testing.T) {
+	SetExporterID(0)
+
+	prev := SetExporterID(42)
+	if prev != 0 {
+		t.Errorf("SetExporterID(42) returned %d; want 0", prev)
+	}
+
+	id := NextExporterID()
+	if id != 42 {
+		t.Errorf("NextExporterID() = %d; want 42", id)
+	}
+}
+
+func TestNextExporterIDConcurrentSafe(t *testing.T) {
+	SetExporterID(0)
+
+	const goroutines = 100
+	const increments = 10
+
+	var wg sync.WaitGroup
+	wg.Add(goroutines)
+
+	for range goroutines {
+		go func() {
+			defer wg.Done()
+			for range increments {
+				NextExporterID()
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	expected := int64(goroutines * increments)
+	if id := NextExporterID(); id != expected {
+		t.Errorf("NextExporterID() = %d; want %d", id, expected)
+	}
+}