otelslog: Split code attributes (open-telemetry#6415)

Follow semantic conventions more strictly. See the following thread:
open-telemetry/semantic-conventions#1624 (comment)

Follows
open-telemetry#6253

There is no noticeable performance overhead:

```
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/contrib/bridges/otelslog
cpu: Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
                               │   old.txt    │               new.txt               │
                               │    sec/op    │   sec/op     vs base                │
Handler/(WithSource).Handle-16   260.4n ± 21%   234.0n ± 5%  -10.14% (p=0.035 n=10)

                               │  old.txt   │            new.txt             │
                               │    B/op    │    B/op     vs base            │
Handler/(WithSource).Handle-16   248.0 ± 0%   248.0 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal

                               │  old.txt   │            new.txt             │
                               │ allocs/op  │ allocs/op   vs base            │
Handler/(WithSource).Handle-16   2.000 ± 0%   2.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal
```

CHANGELOG.md

@@ -28,6 +28,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Fixed the value for configuring the OTLP exporter to use `grpc` instead of `grpc/protobuf` in `go.opentelemetry.io/contrib/config`. (#6338)
 - Allow marshaling types in `go.opentelemetry.io/contrib/config`. (#6347)
 - Removed the redundant handling of panic from the `HTML` function in `go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin`. (#6373)
+- The `code.function` attribute emitted by `go.opentelemetry.io/contrib/bridges/otelslog` now stores just the function name instead the package path-qualified function name. The `code.namespace` attribute now stores the package path. (#6415)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

bridges/otelslog/handler.go

@@ -50,6 +50,7 @@ import (
 	"log/slog"
 	"runtime"
 	"slices"
+	"strings"
 
 	"go.opentelemetry.io/otel/log"
 	"go.opentelemetry.io/otel/log/global"
@@ -192,9 +193,11 @@ func (h *Handler) convertRecord(r slog.Record) log.Record {
 	if h.source {
 		fs := runtime.CallersFrames([]uintptr{r.PC})
 		f, _ := fs.Next()
+		funcName, namespace := splitFuncName(f.Function)
 		record.AddAttributes(
 			log.String(string(semconv.CodeFilepathKey), f.File),
-			log.String(string(semconv.CodeFunctionKey), f.Function),
+			log.String(string(semconv.CodeFunctionKey), funcName),
+			log.String(string(semconv.CodeNamespaceKey), namespace),
 			log.Int(string(semconv.CodeLineNumberKey), f.Line),
 		)
 	}
@@ -476,3 +479,15 @@ func convert(v slog.Value) log.Value {
 		return log.StringValue(fmt.Sprintf("unhandled: (%s) %+v", v.Kind(), v.Any()))
 	}
 }
+
+// splitFuncName splits package path-qualified function name into
+// function name and package full name (namespace). E.g. it splits
+// "github.com/my/repo/pkg.foo" into
+// "foo" and "github.com/my/repo/pkg".
+func splitFuncName(f string) (string, string) {
+	i := strings.LastIndexByte(f, '.')
+	if i < 0 {
+		return "", ""
+	}
+	return f[i+1:], f[:i]
+}

bridges/otelslog/handler_test.go

@@ -230,7 +230,7 @@ func (h *wrapper) Handle(ctx context.Context, r slog.Record) error {
 func TestSLogHandler(t *testing.T) {
 	// Capture the PC of this line
 	pc, file, line, _ := runtime.Caller(0)
-	funcName := runtime.FuncForPC(pc).Name()
+	funcName, namespace := splitFuncName(runtime.FuncForPC(pc).Name())
 
 	cases := []testCase{
 		{
@@ -414,6 +414,7 @@ func TestSLogHandler(t *testing.T) {
 			checks: [][]check{{
 				hasAttr(string(semconv.CodeFilepathKey), file),
 				hasAttr(string(semconv.CodeFunctionKey), funcName),
+				hasAttr(string(semconv.CodeNamespaceKey), namespace),
 				hasAttr(string(semconv.CodeLineNumberKey), int64(line)),
 			}},
 			options: []Option{WithSource(true)},
@@ -510,6 +511,42 @@ func TestHandlerEnabled(t *testing.T) {
 	assert.True(t, h.Enabled(ctx, slog.LevelDebug), "context not passed")
 }
 
+func TestSplitFuncName(t *testing.T) {
+	testCases := []struct {
+		fullFuncName  string
+		wantFuncName  string
+		wantNamespace string
+	}{
+		{
+			fullFuncName:  "github.com/my/repo/pkg.foo",
+			wantFuncName:  "foo",
+			wantNamespace: "github.com/my/repo/pkg",
+		},
+		{
+			fullFuncName:  "net/http.Get",
+			wantFuncName:  "Get",
+			wantNamespace: "net/http",
+		},
+		{
+			fullFuncName:  "invalid",
+			wantFuncName:  "",
+			wantNamespace: "",
+		},
+		{
+			fullFuncName:  ".",
+			wantFuncName:  "",
+			wantNamespace: "",
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.fullFuncName, func(t *testing.T) {
+			gotFuncName, gotNamespace := splitFuncName(tc.fullFuncName)
+			assert.Equal(t, tc.wantFuncName, gotFuncName)
+			assert.Equal(t, tc.wantNamespace, gotNamespace)
+		})
+	}
+}
+
 func BenchmarkHandler(b *testing.B) {
 	var (
 		h   slog.Handler
@@ -639,5 +676,18 @@ func BenchmarkHandler(b *testing.B) {
 		})
 	})
 
+	b.Run("(WithSource).Handle", func(b *testing.B) {
+		handlers := make([]*Handler, b.N)
+		for i := range handlers {
+			handlers[i] = NewHandler("", WithSource(true))
+		}
+
+		b.ReportAllocs()
+		b.ResetTimer()
+		for n := 0; n < b.N; n++ {
+			err = handlers[n].Handle(ctx, record)
+		}
+	})
+
 	_, _ = h, err
 }