add SetSlogLogger

This is syntactic sugar, but it's still useful because it hides logr from
developers who only care about klog and slog.

contextual_slog.go

@@ -0,0 +1,31 @@
+//go:build go1.21
+// +build go1.21
+
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package klog
+
+import (
+	"log/slog"
+
+	"github.com/go-logr/logr"
+)
+
+// SetSlogLogger reconfigures klog to log through the slog logger. The logger must not be nil.
+func SetSlogLogger(logger *slog.Logger) {
+	SetLoggerWithOptions(logr.FromSlogHandler(logger.Handler()), ContextualLogger(true))
+}

contextual_slog_example_test.go

@@ -0,0 +1,48 @@
+//go:build go1.21
+// +build go1.21
+
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package klog_test
+
+import (
+	"log/slog"
+	"os"
+
+	"k8s.io/klog/v2"
+)
+
+func ExampleSetSlogLogger() {
+	state := klog.CaptureState()
+	defer state.Restore()
+
+	handler := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+		ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
+			if a.Key == slog.TimeKey {
+				// Avoid non-deterministic output.
+				return slog.Attr{}
+			}
+			return a
+		},
+	})
+	logger := slog.New(handler)
+	klog.SetSlogLogger(logger)
+	klog.Info("hello world")
+
+	// Output:
+	// level=INFO msg="hello world"
+}