feat: Prevent Init without Setup

Author: heyvito

consistency/consistency_test.go

@@ -12,6 +12,7 @@ import (
 	ioprometheusclient "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/expfmt"
 	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/otel/metric/noop"
 
 	"github.com/ofeefo/em"
 )
@@ -44,8 +45,11 @@ func TestLabelConsistency(t *testing.T) {
 	// sample.txt is the raw payload of the complete_example /metrics endpoint.
 	data, err := os.ReadFile("./raw.txt")
 	require.NoError(t, err)
+	em.SetupWithMeter(noop.Meter{})
+	obj, err := em.Init[metrics]()
+	require.NoError(t, err)
 
-	ids := getAllIds(t, metrics{})
+	ids := getAllIds(t, obj)
 
 	p := &expfmt.TextParser{}
 	mfs, err := p.TextToMetricFamilies(bytes.NewBuffer(data))

initializer.go

@@ -16,6 +16,9 @@ func MustInit[T any](attrs ...attribute.KeyValue) *T {
 }
 
 func Init[T any](attrs ...attribute.KeyValue) (*T, error) {
+	if !p.ready {
+		return nil, fmt.Errorf("em.Init called before em.Setup")
+	}
 	base := new(T)
 	if err := initRef(base, attrs...); err != nil {
 		return nil, err
@@ -43,15 +46,24 @@ func initRef(base any, attrs ...attribute.KeyValue) error {
 			continue
 		}
 
-		fieldIface := fieldVal.Interface()
+		var fieldIface any
+		if fieldVal.Type().Kind() == reflect.Ptr {
+			fieldIface = reflect.New(fieldVal.Type().Elem()).Interface()
+		} else {
+			fieldIface = fieldVal.Addr().Interface()
+		}
 		builder, ok := fieldIface.(buildable)
 
 		switch {
 		case ok:
 			if err := builder.init(field, attrs...); err != nil {
 				return err
 			}
-			fieldVal.Set(reflect.ValueOf(builder))
+			if fieldVal.Kind() == reflect.Ptr {
+				fieldVal.Set(reflect.ValueOf(builder))
+			} else {
+				fieldVal.Set(reflect.ValueOf(builder).Elem())
+			}
 
 		case fieldVal.Kind() == reflect.Struct:
 			if fieldVal.CanAddr() {
@@ -71,6 +83,7 @@ func initRef(base any, attrs ...attribute.KeyValue) error {
 			if err := initNested(field, n, fieldVal, attrs...); err != nil {
 				return err
 			}
+			fieldVal.Set(n)
 		}
 	}
 	return nil

initializer_test.go

@@ -6,6 +6,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric/noop"
 )
 
 type metrics struct {
@@ -24,6 +25,7 @@ type nested struct {
 		Counter Counter[float64] `id:"example_more_nested_counter"`
 	}
 }
+
 type Embedded struct {
 	Histogram     Histogram[int64]     `id:"example_embedded_histogram"`
 	UpDownCounter UpDownCounter[int64] `id:"example_embedded_updowncounter"`
@@ -50,6 +52,7 @@ func mustSetup(t *testing.T, attrs ...attribute.KeyValue) {
 func initAndCall(t *testing.T) func() {
 	t.Helper()
 	return func() {
+		SetupWithMeter(noop.Meter{})
 		var m *metrics
 		require.NotPanics(t, func() { m = MustInit[metrics]() })
 		require.NotPanics(t, func() {

provider.go

@@ -1,19 +1,26 @@
 package em
 
 import (
+	"sync"
+
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/exporters/prometheus"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/noop"
 	m2 "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/resource"
 	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
 )
 
 type provider struct {
-	m metric.Meter
+	m     metric.Meter
+	ready bool
+	mu    sync.Mutex
 }
 
-var p *provider = nil
+var p = &provider{
+	m: noop.Meter{},
+}
 
 func MustSetup(name string, attrs ...attribute.KeyValue) {
 	if err := Setup(name, attrs...); err != nil {
@@ -22,15 +29,18 @@ func MustSetup(name string, attrs ...attribute.KeyValue) {
 }
 
 func SetupWithMeter(meter metric.Meter) {
-	if p != nil {
-		p.m = meter
-	} else {
-		p = &provider{m: meter}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if meter == nil {
+		panic("nil meter provided to SetupWithMeter")
 	}
+	p = &provider{m: meter, ready: true}
 }
 
 func Setup(name string, attrs ...attribute.KeyValue) error {
-	if p != nil {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.ready {
 		return nil
 	}
 
@@ -41,6 +51,7 @@ func Setup(name string, attrs ...attribute.KeyValue) error {
 
 	res := resource.NewWithAttributes(semconv.SchemaURL, attrs...)
 	exp := m2.NewMeterProvider(m2.WithReader(promEx), m2.WithResource(res))
-	p = &provider{m: exp.Meter(name)}
+	p.m = exp.Meter(name)
+	p.ready = true
 	return nil
 }