otelzap: Implement With method (#5653)

Part of
#5191

Pre-work
#5279

This PR implements `With` method

---------

Co-authored-by: Robert Pająk <[email protected]>

bridges/otelzap/core.go

@@ -7,6 +7,7 @@ package otelzap // import "go.opentelemetry.io/contrib/bridges/otelzap"
 
 import (
 	"context"
+	"slices"
 
 	"go.uber.org/zap/zapcore"
 
@@ -88,6 +89,7 @@ func WithLoggerProvider(provider log.LoggerProvider) Option {
 // Core is a [zapcore.Core] that sends logging records to OpenTelemetry.
 type Core struct {
 	logger log.Logger
+	attr   []log.KeyValue
 }
 
 // Compile-time check *Core implements zapcore.Core.
@@ -108,10 +110,20 @@ func (o *Core) Enabled(level zapcore.Level) bool {
 	return o.logger.Enabled(context.Background(), r)
 }
 
-// TODO
 // With adds structured context to the Core.
 func (o *Core) With(fields []zapcore.Field) zapcore.Core {
-	return o
+	cloned := o.clone()
+	if len(fields) > 0 {
+		cloned.attr = append(cloned.attr, convertField(fields)...)
+	}
+	return cloned
+}
+
+func (o *Core) clone() *Core {
+	return &Core{
+		logger: o.logger,
+		attr:   slices.Clone(o.attr),
+	}
 }
 
 // TODO
@@ -143,9 +155,9 @@ func (o *Core) Write(ent zapcore.Entry, fields []zapcore.Field) error {
 	// TODO: Handle zap.Array.
 	// TODO: Handle ent.LoggerName.
 
+	r.AddAttributes(o.attr...)
 	if len(fields) > 0 {
-		attrbuf := convertField(fields)
-		r.AddAttributes(attrbuf...)
+		r.AddAttributes(convertField(fields)...)
 	}
 
 	o.logger.Emit(context.Background(), r)

bridges/otelzap/core_test.go

@@ -29,16 +29,61 @@ func TestCore(t *testing.T) {
 	zc := NewCore(loggerName, WithLoggerProvider(rec))
 	logger := zap.New(zc)
 
-	logger.Info(testMessage, zap.String(testKey, testValue))
+	t.Run("Write", func(t *testing.T) {
+		logger.Info(testMessage, zap.String(testKey, testValue))
+		got := rec.Result()[0].Records[0]
+		assert.Equal(t, testMessage, got.Body().AsString())
+		assert.Equal(t, log.SeverityInfo, got.Severity())
+		assert.Equal(t, 1, got.AttributesLen())
+		got.WalkAttributes(func(kv log.KeyValue) bool {
+			assert.Equal(t, testKey, string(kv.Key))
+			assert.Equal(t, testValue, value2Result(kv.Value))
+			return true
+		})
+	})
 
-	got := rec.Result()[0].Records[0]
-	assert.Equal(t, testMessage, got.Body().AsString())
-	assert.Equal(t, log.SeverityInfo, got.Severity())
-	assert.Equal(t, 1, got.AttributesLen())
-	got.WalkAttributes(func(kv log.KeyValue) bool {
-		assert.Equal(t, testKey, string(kv.Key))
-		assert.Equal(t, testValue, value2Result(kv.Value))
-		return true
+	rec.Reset()
+
+	// test child logger with accumulated fields
+	t.Run("With", func(t *testing.T) {
+		testCases := [][]string{{"test1", "value1"}, {"test2", "value2"}}
+		childlogger := logger.With(zap.String(testCases[0][0], testCases[0][1]))
+		childlogger.Info(testMessage, zap.String(testCases[1][0], testCases[1][1]))
+
+		got := rec.Result()[0].Records[0]
+		assert.Equal(t, testMessage, got.Body().AsString())
+		assert.Equal(t, log.SeverityInfo, got.Severity())
+		assert.Equal(t, 2, got.AttributesLen())
+
+		index := 0
+		got.WalkAttributes(func(kv log.KeyValue) bool {
+			assert.Equal(t, testCases[index][0], string(kv.Key))
+			assert.Equal(t, testCases[index][1], value2Result(kv.Value))
+			index++
+			return true
+		})
+	})
+
+	rec.Reset()
+
+	t.Run("WithMultiple", func(t *testing.T) {
+		testCases := [][]string{{"test1", "value1"}, {"test2", "value2"}, {"test3", "value3"}}
+		childlogger := logger.With(zap.String(testCases[0][0], testCases[0][1]))
+		childlogger2 := childlogger.With(zap.String(testCases[1][0], testCases[1][1]))
+		childlogger2.Info(testMessage, zap.String(testCases[2][0], testCases[2][1]))
+
+		got := rec.Result()[0].Records[0]
+		assert.Equal(t, testMessage, got.Body().AsString())
+		assert.Equal(t, log.SeverityInfo, got.Severity())
+		assert.Equal(t, 3, got.AttributesLen())
+
+		index := 0
+		got.WalkAttributes(func(kv log.KeyValue) bool {
+			assert.Equal(t, testCases[index][0], string(kv.Key))
+			assert.Equal(t, testCases[index][1], value2Result(kv.Value))
+			index++
+			return true
+		})
 	})
 }