AddStacktrace: Use slog.Level, rename to AddStacktraceAt

Changes AddStacktrace to use a slog.Level instead of a Zap Level,
and renames it to AddStacktraceAt.
This leaves room for a LevelEnabler (as suggested in the PR)
to be specified with an AddStacktrace in the future.

exp/zapslog/handler.go

@@ -37,16 +37,16 @@ type Handler struct {
 	core       zapcore.Core
 	name       string // logger name
 	addCaller  bool
-	addStack   zapcore.LevelEnabler
+	addStackAt slog.Level
 	callerSkip int
 }
 
 // NewHandler builds a [Handler] that writes to the supplied [zapcore.Core]
 // with options.
 func NewHandler(core zapcore.Core, opts ...Option) *Handler {
 	h := &Handler{
-		core:     core,
-		addStack: zapcore.ErrorLevel,
+		core:       core,
+		addStackAt: slog.LevelError,
 	}
 	for _, v := range opts {
 		v.apply(h)
@@ -145,7 +145,7 @@ func (h *Handler) Handle(ctx context.Context, record slog.Record) error {
 		}
 	}
 
-	if h.addStack.Enabled(zapLevel) {
+	if record.Level >= h.addStackAt {
 		// Skipping 3:
 		// zapslog/handler log/slog.(*Logger).log
 		// slog/logger log/slog.(*Logger).log

exp/zapslog/handler_test.go

@@ -50,7 +50,7 @@ func TestAddCaller(t *testing.T) {
 func TestAddStack(t *testing.T) {
 	r := require.New(t)
 	fac, logs := observer.New(zapcore.DebugLevel)
-	sl := slog.New(NewHandler(fac, AddStacktrace(zapcore.DebugLevel)))
+	sl := slog.New(NewHandler(fac, AddStacktrace(slog.LevelDebug)))
 	sl.Info("msg")
 
 	r.Len(logs.AllUntimed(), 1, "Expected exactly one entry to be logged")

exp/zapslog/options.go

@@ -22,7 +22,7 @@
 
 package zapslog
 
-import "go.uber.org/zap/zapcore"
+import "log/slog"
 
 // An Option configures a slog Handler.
 type Option interface {
@@ -64,10 +64,10 @@ func WithCallerSkip(skip int) Option {
 	})
 }
 
-// AddStacktrace configures the Logger to record a stack trace for all messages at
-// or above a given level.
-func AddStacktrace(lvl zapcore.LevelEnabler) Option {
+// AddStacktraceAt configures the Logger to record a stack trace
+// for all messages at or above a given level.
+func AddStacktraceAt(lvl slog.Level) Option {
 	return optionFunc(func(log *Handler) {
-		log.addStack = lvl
+		log.addStackAt = lvl
 	})
 }