log/slog: built-in handler constructors take options as a second arg

There is now one constructor function for each built-in handler, with
signature

    NewXXXHandler(io.Writer, *HandlerOptions) *XXXHandler

Fixes #59339.

Change-Id: Ia02183c5ce0dc15c64e33ad05fd69bca09df2d2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/486415
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Jonathan Amsterdam <jba@google.com>

api/next/56345.txt

@@ -58,10 +58,8 @@ pkg log/slog, func IntValue(int) Value #56345
 pkg log/slog, func Log(context.Context, Level, string, ...interface{}) #56345
 pkg log/slog, func LogAttrs(context.Context, Level, string, ...Attr) #56345
 pkg log/slog, func New(Handler) *Logger #56345
-pkg log/slog, func NewJSONHandler(io.Writer) *JSONHandler #56345
 pkg log/slog, func NewLogLogger(Handler, Level) *log.Logger #56345
 pkg log/slog, func NewRecord(time.Time, Level, string, uintptr) Record #56345
-pkg log/slog, func NewTextHandler(io.Writer) *TextHandler #56345
 pkg log/slog, func SetDefault(*Logger) #56345
 pkg log/slog, func String(string, string) Attr #56345
 pkg log/slog, func StringValue(string) Value #56345
@@ -105,8 +103,6 @@ pkg log/slog, method (*TextHandler) WithAttrs([]Attr) Handler #56345
 pkg log/slog, method (*TextHandler) WithGroup(string) Handler #56345
 pkg log/slog, method (Attr) Equal(Attr) bool #56345
 pkg log/slog, method (Attr) String() string #56345
-pkg log/slog, method (HandlerOptions) NewJSONHandler(io.Writer) *JSONHandler #56345
-pkg log/slog, method (HandlerOptions) NewTextHandler(io.Writer) *TextHandler #56345
 pkg log/slog, method (Kind) String() string #56345
 pkg log/slog, method (Level) Level() Level #56345
 pkg log/slog, method (Level) MarshalJSON() ([]uint8, error) #56345

api/next/59339.txt

@@ -0,0 +1,2 @@
+pkg log/slog, func NewJSONHandler(io.Writer, *HandlerOptions) *JSONHandler #59339
+pkg log/slog, func NewTextHandler(io.Writer, *HandlerOptions) *TextHandler #59339

src/log/slog/doc.go

@@ -44,7 +44,7 @@ For more control over the output format, create a logger with a different handle
 This statement uses [New] to create a new logger with a TextHandler
 that writes structured records in text form to standard error:
 
-	logger := slog.New(slog.NewTextHandler(os.Stderr))
+	logger := slog.New(slog.NewTextHandler(os.Stderr, nil))
 
 [TextHandler] output is a sequence of key=value pairs, easily and unambiguously
 parsed by machine. This statement:
@@ -57,7 +57,7 @@ produces this output:
 
 The package also provides [JSONHandler], whose output is line-delimited JSON:
 
-	logger := slog.New(slog.NewJSONHandler(os.Stdout))
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
 	logger.Info("hello", "count", 3)
 
 produces this output:
@@ -149,7 +149,7 @@ a global LevelVar:
 
 Then use the LevelVar to construct a handler, and make it the default:
 
-	h := slog.HandlerOptions{Level: programLevel}.NewJSONHandler(os.Stderr)
+	h := slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{Level: programLevel})
 	slog.SetDefault(slog.New(h))
 
 Now the program can change its logging level with a single statement:

src/log/slog/example_custom_levels_test.go

@@ -25,7 +25,7 @@ func ExampleHandlerOptions_customLevels() {
 		LevelEmergency = slog.Level(12)
 	)
 
-	th := slog.HandlerOptions{
+	th := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
 		// Set a custom level to show all log output. The default value is
 		// LevelInfo, which would drop Debug and Trace logs.
 		Level: LevelTrace,
@@ -69,7 +69,7 @@ func ExampleHandlerOptions_customLevels() {
 
 			return a
 		},
-	}.NewTextHandler(os.Stdout)
+	})
 
 	logger := slog.New(th)
 	logger.Log(nil, LevelEmergency, "missing pilots")

src/log/slog/example_level_handler_test.go

@@ -63,7 +63,7 @@ func (h *LevelHandler) Handler() slog.Handler {
 // Another typical use would be to decrease the log level (to LevelDebug, say)
 // during a part of the program that was suspected of containing a bug.
 func ExampleHandler_levelHandler() {
-	th := slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime}.NewTextHandler(os.Stdout)
+	th := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime})
 	logger := slog.New(NewLevelHandler(slog.LevelWarn, th))
 	logger.Info("not printed")
 	logger.Warn("printed")

src/log/slog/example_logvaluer_secret_test.go

@@ -23,8 +23,7 @@ func (Token) LogValue() slog.Value {
 // with an alternative representation to avoid revealing secrets.
 func ExampleLogValuer_secret() {
 	t := Token("shhhh!")
-	logger := slog.New(slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime}.
+	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime}))
-		NewTextHandler(os.Stdout))
 	logger.Info("permission granted", "user", "Perry", "token", t)
 
 	// Output:

src/log/slog/example_test.go

@@ -16,7 +16,7 @@ func ExampleGroup() {
 	r, _ := http.NewRequest("GET", "localhost", nil)
 	// ...
 
-	logger := slog.New(slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime}.NewTextHandler(os.Stdout))
+	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{ReplaceAttr: slogtest.RemoveTime}))
 	logger.Info("finished",
 		slog.Group("req",
 			slog.String("method", r.Method),

src/log/slog/example_wrap_test.go

@@ -39,7 +39,7 @@ func Example_wrapping() {
 		}
 		return a
 	}
-	logger := slog.New(slog.HandlerOptions{AddSource: true, ReplaceAttr: replace}.NewTextHandler(os.Stdout))
+	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{AddSource: true, ReplaceAttr: replace}))
 	Infof(logger, "message, %s", "formatted")
 
 	// Output:

src/log/slog/handler_test.go

@@ -338,8 +338,8 @@ func TestJSONAndTextHandlers(t *testing.T) {
 				h    Handler
 				want string
 			}{
-				{"text", opts.NewTextHandler(&buf), test.wantText},
+				{"text", NewTextHandler(&buf, &opts), test.wantText},
-				{"json", opts.NewJSONHandler(&buf), test.wantJSON},
+				{"json", NewJSONHandler(&buf, &opts), test.wantJSON},
 			} {
 				t.Run(handler.name, func(t *testing.T) {
 					h := handler.h
@@ -419,7 +419,7 @@ func TestSecondWith(t *testing.T) {
 	// Verify that a second call to Logger.With does not corrupt
 	// the original.
 	var buf bytes.Buffer
-	h := HandlerOptions{ReplaceAttr: removeKeys(TimeKey)}.NewTextHandler(&buf)
+	h := NewTextHandler(&buf, &HandlerOptions{ReplaceAttr: removeKeys(TimeKey)})
 	logger := New(h).With(
 		String("app", "playground"),
 		String("role", "tester"),
@@ -445,14 +445,14 @@ func TestReplaceAttrGroups(t *testing.T) {
 
 	var got []ga
 
-	h := HandlerOptions{ReplaceAttr: func(gs []string, a Attr) Attr {
+	h := NewTextHandler(io.Discard, &HandlerOptions{ReplaceAttr: func(gs []string, a Attr) Attr {
 		v := a.Value.String()
 		if a.Key == TimeKey {
 			v = "<now>"
 		}
 		got = append(got, ga{strings.Join(gs, ","), a.Key, v})
 		return a
-	}}.NewTextHandler(io.Discard)
+	}})
 	New(h).
 		With(Int("a", 1)).
 		WithGroup("g1").

src/log/slog/internal/benchmarks/benchmarks_test.go

@@ -32,8 +32,8 @@ func BenchmarkAttrs(b *testing.B) {
 		{"disabled", disabledHandler{}, false},
 		{"async discard", newAsyncHandler(), true},
 		{"fastText discard", newFastTextHandler(io.Discard), false},
-		{"Text discard", slog.NewTextHandler(io.Discard), false},
+		{"Text discard", slog.NewTextHandler(io.Discard, nil), false},
-		{"JSON discard", slog.NewJSONHandler(io.Discard), false},
+		{"JSON discard", slog.NewJSONHandler(io.Discard, nil), false},
 	} {
 		logger := slog.New(handler.h)
 		b.Run(handler.name, func(b *testing.B) {

src/log/slog/json_handler.go

@@ -25,18 +25,17 @@ type JSONHandler struct {
 }
 
 // NewJSONHandler creates a JSONHandler that writes to w,
-// using the default options.
+// using the given options.
-func NewJSONHandler(w io.Writer) *JSONHandler {
+// If opts is nil, the default options are used.
-	return (HandlerOptions{}).NewJSONHandler(w)
+func NewJSONHandler(w io.Writer, opts *HandlerOptions) *JSONHandler {
-}
+	if opts == nil {
-
+		opts = &HandlerOptions{}
-// NewJSONHandler creates a JSONHandler with the given options that writes to w.
+	}
-func (opts HandlerOptions) NewJSONHandler(w io.Writer) *JSONHandler {
 	return &JSONHandler{
 		&commonHandler{
 			json: true,
 			w:    w,
-			opts: opts,
+			opts: *opts,
 		},
 	}
 }

src/log/slog/json_handler_test.go

@@ -39,7 +39,7 @@ func TestJSONHandler(t *testing.T) {
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			var buf bytes.Buffer
-			h := test.opts.NewJSONHandler(&buf)
+			h := NewJSONHandler(&buf, &test.opts)
 			r := NewRecord(testTime, LevelInfo, "m", 0)
 			r.AddAttrs(Int("a", 1), Any("m", map[string]int{"b": 2}))
 			if err := h.Handle(context.Background(), r); err != nil {
@@ -171,7 +171,7 @@ func BenchmarkJSONHandler(b *testing.B) {
 		}},
 	} {
 		b.Run(bench.name, func(b *testing.B) {
-			l := New(bench.opts.NewJSONHandler(io.Discard)).With(
+			l := New(NewJSONHandler(io.Discard, &bench.opts)).With(
 				String("program", "my-test-program"),
 				String("package", "log/slog"),
 				String("traceID", "2039232309232309"),
@@ -236,7 +236,7 @@ func BenchmarkPreformatting(b *testing.B) {
 		{"struct file", outFile, structAttrs},
 	} {
 		b.Run(bench.name, func(b *testing.B) {
-			l := New(NewJSONHandler(bench.wc)).With(bench.attrs...)
+			l := New(NewJSONHandler(bench.wc, nil)).With(bench.attrs...)
 			b.ReportAllocs()
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {

src/log/slog/logger_test.go

@@ -27,7 +27,7 @@ const timeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}(Z|[+-]\d{2}:\d{2})`
 func TestLogTextHandler(t *testing.T) {
 	var buf bytes.Buffer
 
-	l := New(NewTextHandler(&buf))
+	l := New(NewTextHandler(&buf, nil))
 
 	check := func(want string) {
 		t.Helper()
@@ -104,13 +104,13 @@ func TestConnections(t *testing.T) {
 
 	// Once slog.SetDefault is called, the direction is reversed: the default
 	// log.Logger's output goes through the handler.
-	SetDefault(New(HandlerOptions{AddSource: true}.NewTextHandler(&slogbuf)))
+	SetDefault(New(NewTextHandler(&slogbuf, &HandlerOptions{AddSource: true})))
 	log.Print("msg2")
 	checkLogOutput(t, slogbuf.String(), "time="+timeRE+` level=INFO source=.*logger_test.go:\d{3} msg=msg2`)
 
 	// The default log.Logger always outputs at Info level.
 	slogbuf.Reset()
-	SetDefault(New(HandlerOptions{Level: LevelWarn}.NewTextHandler(&slogbuf)))
+	SetDefault(New(NewTextHandler(&slogbuf, &HandlerOptions{Level: LevelWarn})))
 	log.Print("should not appear")
 	if got := slogbuf.String(); got != "" {
 		t.Errorf("got %q, want empty", got)
@@ -352,7 +352,7 @@ func TestLoggerError(t *testing.T) {
 		}
 		return a
 	}
-	l := New(HandlerOptions{ReplaceAttr: removeTime}.NewTextHandler(&buf))
+	l := New(NewTextHandler(&buf, &HandlerOptions{ReplaceAttr: removeTime}))
 	l.Error("msg", "err", io.EOF, "a", 1)
 	checkLogOutput(t, buf.String(), `level=ERROR msg=msg err=EOF a=1`)
 	buf.Reset()
@@ -362,7 +362,7 @@ func TestLoggerError(t *testing.T) {
 
 func TestNewLogLogger(t *testing.T) {
 	var buf bytes.Buffer
-	h := NewTextHandler(&buf)
+	h := NewTextHandler(&buf, nil)
 	ll := NewLogLogger(h, LevelWarn)
 	ll.Print("hello")
 	checkLogOutput(t, buf.String(), "time="+timeRE+` level=WARN msg=hello`)

src/log/slog/text_handler.go

@@ -22,18 +22,17 @@ type TextHandler struct {
 }
 
 // NewTextHandler creates a TextHandler that writes to w,
-// using the default options.
+// using the given options.
-func NewTextHandler(w io.Writer) *TextHandler {
+// If opts is nil, the default options are used.
-	return (HandlerOptions{}).NewTextHandler(w)
+func NewTextHandler(w io.Writer, opts *HandlerOptions) *TextHandler {
-}
+	if opts == nil {
-
+		opts = &HandlerOptions{}
-// NewTextHandler creates a TextHandler with the given options that writes to w.
+	}
-func (opts HandlerOptions) NewTextHandler(w io.Writer) *TextHandler {
 	return &TextHandler{
 		&commonHandler{
 			json: false,
 			w:    w,
-			opts: opts,
+			opts: *opts,
 		},
 	}
 }

src/log/slog/text_handler_test.go

@@ -82,7 +82,7 @@ func TestTextHandler(t *testing.T) {
 			} {
 				t.Run(opts.name, func(t *testing.T) {
 					var buf bytes.Buffer
-					h := opts.opts.NewTextHandler(&buf)
+					h := NewTextHandler(&buf, &opts.opts)
 					r := NewRecord(testTime, LevelInfo, "a message", 0)
 					r.AddAttrs(test.attr)
 					if err := h.Handle(context.Background(), r); err != nil {
@@ -124,7 +124,7 @@ func (t text) MarshalText() ([]byte, error) {
 
 func TestTextHandlerPreformatted(t *testing.T) {
 	var buf bytes.Buffer
-	var h Handler = NewTextHandler(&buf)
+	var h Handler = NewTextHandler(&buf, nil)
 	h = h.WithAttrs([]Attr{Duration("dur", time.Minute), Bool("b", true)})
 	// Also test omitting time.
 	r := NewRecord(time.Time{}, 0 /* 0 Level is INFO */, "m", 0)
@@ -145,7 +145,7 @@ func TestTextHandlerAlloc(t *testing.T) {
 	for i := 0; i < 10; i++ {
 		r.AddAttrs(Int("x = y", i))
 	}
-	var h Handler = NewTextHandler(io.Discard)
+	var h Handler = NewTextHandler(io.Discard, nil)
 	wantAllocs(t, 0, func() { h.Handle(context.Background(), r) })
 
 	h = h.WithGroup("s")

src/testing/slogtest/example_test.go

@@ -19,7 +19,7 @@ import (
 // format when given a pointer to a map[string]any.
 func Example_parsing() {
 	var buf bytes.Buffer
-	h := slog.NewJSONHandler(&buf)
+	h := slog.NewJSONHandler(&buf, nil)
 
 	results := func() []map[string]any {
 		var ms []map[string]any