feat(otelslog): add WithSource option

Add a slogbridge option to include the source file location in the log attributes

bridges/otelslog/handler.go

@@ -48,6 +48,7 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"runtime"
 	"slices"
 
 	"go.opentelemetry.io/otel/log"
@@ -64,6 +65,7 @@ type config struct {
 	provider  log.LoggerProvider
 	version   string
 	schemaURL string
+	source    bool
 }
 
 func newConfig(options []Option) config {
@@ -131,6 +133,15 @@ func WithLoggerProvider(provider log.LoggerProvider) Option {
 	})
 }
 
+// WithSource returns an [Option] that configures the [log.Logger] to include
+// the source location of the log record in log attributes.
+func WithSource(source bool) Option {
+	return optFunc(func(c config) config {
+		c.source = source
+		return c
+	})
+}
+
 // Handler is an [slog.Handler] that sends all logging records it receives to
 // OpenTelemetry. See package documentation for how conversions are made.
 type Handler struct {
@@ -140,6 +151,8 @@ type Handler struct {
 	attrs  *kvBuffer
 	group  *group
 	logger log.Logger
+
+	source bool
 }
 
 // Compile-time check *Handler implements slog.Handler.
@@ -155,7 +168,10 @@ var _ slog.Handler = (*Handler)(nil)
 // [log.Logger] implementation may override this value with a default.
 func NewHandler(name string, options ...Option) *Handler {
 	cfg := newConfig(options)
-	return &Handler{logger: cfg.logger(name)}
+	return &Handler{
+		logger: cfg.logger(name),
+		source: cfg.source,
+	}
 }
 
 // Handle handles the passed record.
@@ -172,6 +188,16 @@ func (h *Handler) convertRecord(r slog.Record) log.Record {
 	const sevOffset = slog.Level(log.SeverityDebug) - slog.LevelDebug
 	record.SetSeverity(log.Severity(r.Level + sevOffset))
 
+	if h.source {
+		fs := runtime.CallersFrames([]uintptr{r.PC})
+		f, _ := fs.Next()
+		record.AddAttributes(log.Map("source",
+			log.String("function", f.Function),
+			log.String("file", f.File),
+			log.Int("line", f.Line)),
+		)
+	}
+
 	if h.attrs.Len() > 0 {
 		record.AddAttributes(h.attrs.KeyValues()...)
 	}

bridges/otelslog/handler_test.go

@@ -455,6 +455,7 @@ func TestNewHandlerConfiguration(t *testing.T) {
 				WithLoggerProvider(r),
 				WithVersion("ver"),
 				WithSchemaURL("url"),
+				WithSource(true),
 			)
 		})
 		require.NotNil(t, h.logger)
@@ -611,3 +612,57 @@ func BenchmarkHandler(b *testing.B) {
 
 	_, _ = h, err
 }
+
+func TestHandler_convertRecord(t *testing.T) {
+	// Capture the PC of this line
+	pc, file, line, _ := runtime.Caller(0)
+	funcName := runtime.FuncForPC(pc).Name()
+
+	tests := []struct {
+		name      string
+		handler   Handler
+		wantAttrs []log.KeyValue
+	}{
+		{
+			name:      "empty",
+			handler:   Handler{},
+			wantAttrs: []log.KeyValue{},
+		},
+		{
+			name:    "with source",
+			handler: Handler{source: true},
+			wantAttrs: []log.KeyValue{
+				{Key: "source", Value: log.MapValue(
+					log.String("function", funcName),
+					log.String("file", file),
+					log.Int("line", line),
+				)},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			slogRecord := slog.NewRecord(time.Now(), slog.LevelInfo, "body", pc)
+			record := tt.handler.convertRecord(slogRecord)
+
+			// Validate attributes
+			attrMap := make(map[string]bool)
+			for _, attr := range tt.wantAttrs {
+				attrMap[attr.String()] = true
+			}
+
+			record.WalkAttributes(func(kv log.KeyValue) bool {
+				if !attrMap[kv.String()] {
+					t.Errorf("Unexpected attribute: %v", kv)
+					return false
+				}
+				delete(attrMap, kv.String())
+				return true
+			})
+
+			if len(attrMap) > 0 {
+				t.Errorf("Missing expected attributes: %v", attrMap)
+			}
+		})
+	}
+}