log/slog: replace nil contexts with context.Background()

Passing nil for a context is discouraged. We should avoid it.

Fixes #61219.

Change-Id: I664387070aacb56af580b6b0791ca40982d2a711
Reviewed-on: https://go-review.googlesource.com/c/go/+/508437
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/log/slog/doc.go

@@ -206,7 +206,7 @@ keys and values; this allows it, too, to avoid allocation.
 
 The call
 
-	logger.LogAttrs(nil, slog.LevelInfo, "hello", slog.Int("count", 3))
+	logger.LogAttrs(ctx, slog.LevelInfo, "hello", slog.Int("count", 3))
 
 is the most efficient way to achieve the same output as
 

src/log/slog/example_custom_levels_test.go

@@ -5,6 +5,7 @@
 package slog_test
 
 import (
+	"context"
 	"log/slog"
 	"os"
 )
@@ -72,13 +73,14 @@ func ExampleHandlerOptions_customLevels() {
 	})
 
 	logger := slog.New(th)
-	logger.Log(nil, LevelEmergency, "missing pilots")
+	ctx := context.Background()
+	logger.Log(ctx, LevelEmergency, "missing pilots")
 	logger.Error("failed to start engines", "err", "missing fuel")
 	logger.Warn("falling back to default value")
-	logger.Log(nil, LevelNotice, "all systems are running")
+	logger.Log(ctx, LevelNotice, "all systems are running")
 	logger.Info("initiating launch")
 	logger.Debug("starting background job")
-	logger.Log(nil, LevelTrace, "button clicked")
+	logger.Log(ctx, LevelTrace, "button clicked")
 
 	// Output:
 	// sev=EMERGENCY msg="missing pilots"

src/log/slog/handler_test.go

@@ -108,8 +108,6 @@ func TestDefaultHandle(t *testing.T) {
 
 // Verify the common parts of TextHandler and JSONHandler.
 func TestJSONAndTextHandlers(t *testing.T) {
-	ctx := context.Background()
-
 	// remove all Attrs
 	removeAll := func(_ []string, a Attr) Attr { return Attr{} }
 
@@ -412,7 +410,7 @@ func TestJSONAndTextHandlers(t *testing.T) {
 						h = test.with(h)
 					}
 					buf.Reset()
-					if err := h.Handle(ctx, r); err != nil {
+					if err := h.Handle(nil, r); err != nil {
 						t.Fatal(err)
 					}
 					want := strings.ReplaceAll(handler.want, "$LINE", line)

src/log/slog/json_handler_test.go

@@ -174,6 +174,7 @@ func BenchmarkJSONHandler(b *testing.B) {
 		}},
 	} {
 		b.Run(bench.name, func(b *testing.B) {
+			ctx := context.Background()
 			l := New(NewJSONHandler(io.Discard, &bench.opts)).With(
 				String("program", "my-test-program"),
 				String("package", "log/slog"),
@@ -182,7 +183,7 @@ func BenchmarkJSONHandler(b *testing.B) {
 			b.ReportAllocs()
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				l.LogAttrs(nil, LevelInfo, "this is a typical log message",
+				l.LogAttrs(ctx, LevelInfo, "this is a typical log message",
 					String("module", "github.com/google/go-cmp"),
 					String("version", "v1.23.4"),
 					Int("count", 23),
@@ -238,12 +239,13 @@ func BenchmarkPreformatting(b *testing.B) {
 		{"struct", io.Discard, structAttrs},
 		{"struct file", outFile, structAttrs},
 	} {
+		ctx := context.Background()
 		b.Run(bench.name, func(b *testing.B) {
 			l := New(NewJSONHandler(bench.wc, nil)).With(bench.attrs...)
 			b.ReportAllocs()
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				l.LogAttrs(nil, LevelInfo, "this is a typical log message",
+				l.LogAttrs(ctx, LevelInfo, "this is a typical log message",
 					String("module", "github.com/google/go-cmp"),
 					String("version", "v1.23.4"),
 					Int("count", 23),

src/log/slog/logger.go

@@ -165,7 +165,7 @@ func (l *Logger) LogAttrs(ctx context.Context, level Level, msg string, attrs ..
 
 // Debug logs at LevelDebug.
 func (l *Logger) Debug(msg string, args ...any) {
-	l.log(nil, LevelDebug, msg, args...)
+	l.log(context.Background(), LevelDebug, msg, args...)
 }
 
 // DebugContext logs at LevelDebug with the given context.
@@ -175,7 +175,7 @@ func (l *Logger) DebugContext(ctx context.Context, msg string, args ...any) {
 
 // Info logs at LevelInfo.
 func (l *Logger) Info(msg string, args ...any) {
-	l.log(nil, LevelInfo, msg, args...)
+	l.log(context.Background(), LevelInfo, msg, args...)
 }
 
 // InfoContext logs at LevelInfo with the given context.
@@ -185,7 +185,7 @@ func (l *Logger) InfoContext(ctx context.Context, msg string, args ...any) {
 
 // Warn logs at LevelWarn.
 func (l *Logger) Warn(msg string, args ...any) {
-	l.log(nil, LevelWarn, msg, args...)
+	l.log(context.Background(), LevelWarn, msg, args...)
 }
 
 // WarnContext logs at LevelWarn with the given context.
@@ -195,7 +195,7 @@ func (l *Logger) WarnContext(ctx context.Context, msg string, args ...any) {
 
 // Error logs at LevelError.
 func (l *Logger) Error(msg string, args ...any) {
-	l.log(nil, LevelError, msg, args...)
+	l.log(context.Background(), LevelError, msg, args...)
 }
 
 // ErrorContext logs at LevelError with the given context.
@@ -247,7 +247,7 @@ func (l *Logger) logAttrs(ctx context.Context, level Level, msg string, attrs ..
 
 // Debug calls Logger.Debug on the default logger.
 func Debug(msg string, args ...any) {
-	Default().log(nil, LevelDebug, msg, args...)
+	Default().log(context.Background(), LevelDebug, msg, args...)
 }
 
 // DebugContext calls Logger.DebugContext on the default logger.
@@ -257,7 +257,7 @@ func DebugContext(ctx context.Context, msg string, args ...any) {
 
 // Info calls Logger.Info on the default logger.
 func Info(msg string, args ...any) {
-	Default().log(nil, LevelInfo, msg, args...)
+	Default().log(context.Background(), LevelInfo, msg, args...)
 }
 
 // InfoContext calls Logger.InfoContext on the default logger.
@@ -267,7 +267,7 @@ func InfoContext(ctx context.Context, msg string, args ...any) {
 
 // Warn calls Logger.Warn on the default logger.
 func Warn(msg string, args ...any) {
-	Default().log(nil, LevelWarn, msg, args...)
+	Default().log(context.Background(), LevelWarn, msg, args...)
 }
 
 // WarnContext calls Logger.WarnContext on the default logger.
@@ -277,7 +277,7 @@ func WarnContext(ctx context.Context, msg string, args ...any) {
 
 // Error calls Logger.Error on the default logger.
 func Error(msg string, args ...any) {
-	Default().log(nil, LevelError, msg, args...)
+	Default().log(context.Background(), LevelError, msg, args...)
 }
 
 // ErrorContext calls Logger.ErrorContext on the default logger.

src/log/slog/logger_test.go

@@ -25,6 +25,7 @@ import (
 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) {
+	ctx := context.Background()
 	var buf bytes.Buffer
 
 	l := New(NewTextHandler(&buf, nil))
@@ -51,10 +52,10 @@ func TestLogTextHandler(t *testing.T) {
 	l.Error("bad", "a", 1)
 	check(`level=ERROR msg=bad a=1`)
 
-	l.Log(nil, LevelWarn+1, "w", Int("a", 1), String("b", "two"))
+	l.Log(ctx, LevelWarn+1, "w", Int("a", 1), String("b", "two"))
 	check(`level=WARN\+1 msg=w a=1 b=two`)
 
-	l.LogAttrs(nil, LevelInfo+1, "a b c", Int("a", 1), String("b", "two"))
+	l.LogAttrs(ctx, LevelInfo+1, "a b c", Int("a", 1), String("b", "two"))
 	check(`level=INFO\+1 msg="a b c" a=1 b=two`)
 
 	l.Info("info", "a", []Attr{Int("i", 1)})
@@ -156,6 +157,7 @@ func TestAttrs(t *testing.T) {
 }
 
 func TestCallDepth(t *testing.T) {
+	ctx := context.Background()
 	h := &captureHandler{}
 	var startLine int
 
@@ -181,9 +183,9 @@ func TestCallDepth(t *testing.T) {
 	startLine = f.Line + 4
 	// Do not change the number of lines between here and the call to check(0).
 
-	logger.Log(nil, LevelInfo, "")
+	logger.Log(ctx, LevelInfo, "")
 	check(0)
-	logger.LogAttrs(nil, LevelInfo, "")
+	logger.LogAttrs(ctx, LevelInfo, "")
 	check(1)
 	logger.Debug("")
 	check(2)
@@ -201,13 +203,14 @@ func TestCallDepth(t *testing.T) {
 	check(8)
 	Error("")
 	check(9)
-	Log(nil, LevelInfo, "")
+	Log(ctx, LevelInfo, "")
 	check(10)
-	LogAttrs(nil, LevelInfo, "")
+	LogAttrs(ctx, LevelInfo, "")
 	check(11)
 }
 
 func TestAlloc(t *testing.T) {
+	ctx := context.Background()
 	dl := New(discardHandler{})
 	defer SetDefault(Default()) // restore
 	SetDefault(dl)
@@ -222,7 +225,7 @@ func TestAlloc(t *testing.T) {
 		wantAllocs(t, 0, func() { dl.Info("hello") })
 	})
 	t.Run("logger.Log", func(t *testing.T) {
-		wantAllocs(t, 0, func() { dl.Log(nil, LevelDebug, "hello") })
+		wantAllocs(t, 0, func() { dl.Log(ctx, LevelDebug, "hello") })
 	})
 	t.Run("2 pairs", func(t *testing.T) {
 		s := "abc"
@@ -239,7 +242,7 @@ func TestAlloc(t *testing.T) {
 		s := "abc"
 		i := 2000
 		wantAllocs(t, 2, func() {
-			l.Log(nil, LevelInfo, "hello",
+			l.Log(ctx, LevelInfo, "hello",
 				"n", i,
 				"s", s,
 			)
@@ -250,8 +253,8 @@ func TestAlloc(t *testing.T) {
 		s := "abc"
 		i := 2000
 		wantAllocs(t, 0, func() {
-			if l.Enabled(nil, LevelInfo) {
+			if l.Enabled(ctx, LevelInfo) {
-				l.Log(nil, LevelInfo, "hello",
+				l.Log(ctx, LevelInfo, "hello",
 					"n", i,
 					"s", s,
 				)
@@ -273,30 +276,30 @@ func TestAlloc(t *testing.T) {
 		wantAllocs(t, 0, func() { dl.Info("", "error", io.EOF) })
 	})
 	t.Run("attrs1", func(t *testing.T) {
-		wantAllocs(t, 0, func() { dl.LogAttrs(nil, LevelInfo, "", Int("a", 1)) })
+		wantAllocs(t, 0, func() { dl.LogAttrs(ctx, LevelInfo, "", Int("a", 1)) })
-		wantAllocs(t, 0, func() { dl.LogAttrs(nil, LevelInfo, "", Any("error", io.EOF)) })
+		wantAllocs(t, 0, func() { dl.LogAttrs(ctx, LevelInfo, "", Any("error", io.EOF)) })
 	})
 	t.Run("attrs3", func(t *testing.T) {
 		wantAllocs(t, 0, func() {
-			dl.LogAttrs(nil, LevelInfo, "hello", Int("a", 1), String("b", "two"), Duration("c", time.Second))
+			dl.LogAttrs(ctx, LevelInfo, "hello", Int("a", 1), String("b", "two"), Duration("c", time.Second))
 		})
 	})
 	t.Run("attrs3 disabled", func(t *testing.T) {
 		logger := New(discardHandler{disabled: true})
 		wantAllocs(t, 0, func() {
-			logger.LogAttrs(nil, LevelInfo, "hello", Int("a", 1), String("b", "two"), Duration("c", time.Second))
+			logger.LogAttrs(ctx, LevelInfo, "hello", Int("a", 1), String("b", "two"), Duration("c", time.Second))
 		})
 	})
 	t.Run("attrs6", func(t *testing.T) {
 		wantAllocs(t, 1, func() {
-			dl.LogAttrs(nil, LevelInfo, "hello",
+			dl.LogAttrs(ctx, LevelInfo, "hello",
 				Int("a", 1), String("b", "two"), Duration("c", time.Second),
 				Int("d", 1), String("e", "two"), Duration("f", time.Second))
 		})
 	})
 	t.Run("attrs9", func(t *testing.T) {
 		wantAllocs(t, 1, func() {
-			dl.LogAttrs(nil, LevelInfo, "hello",
+			dl.LogAttrs(ctx, LevelInfo, "hello",
 				Int("a", 1), String("b", "two"), Duration("c", time.Second),
 				Int("d", 1), String("e", "two"), Duration("f", time.Second),
 				Int("d", 1), String("e", "two"), Duration("f", time.Second))
@@ -511,27 +514,27 @@ func BenchmarkNopLog(b *testing.B) {
 	b.Run("no attrs", func(b *testing.B) {
 		b.ReportAllocs()
 		for i := 0; i < b.N; i++ {
-			l.LogAttrs(nil, LevelInfo, "msg")
+			l.LogAttrs(ctx, LevelInfo, "msg")
 		}
 	})
 	b.Run("attrs", func(b *testing.B) {
 		b.ReportAllocs()
 		for i := 0; i < b.N; i++ {
-			l.LogAttrs(nil, LevelInfo, "msg", Int("a", 1), String("b", "two"), Bool("c", true))
+			l.LogAttrs(ctx, LevelInfo, "msg", Int("a", 1), String("b", "two"), Bool("c", true))
 		}
 	})
 	b.Run("attrs-parallel", func(b *testing.B) {
 		b.ReportAllocs()
 		b.RunParallel(func(pb *testing.PB) {
 			for pb.Next() {
-				l.LogAttrs(nil, LevelInfo, "msg", Int("a", 1), String("b", "two"), Bool("c", true))
+				l.LogAttrs(ctx, LevelInfo, "msg", Int("a", 1), String("b", "two"), Bool("c", true))
 			}
 		})
 	})
 	b.Run("keys-values", func(b *testing.B) {
 		b.ReportAllocs()
 		for i := 0; i < b.N; i++ {
-			l.Log(nil, LevelInfo, "msg", "a", 1, "b", "two", "c", true)
+			l.Log(ctx, LevelInfo, "msg", "a", 1, "b", "two", "c", true)
 		}
 	})
 	b.Run("WithContext", func(b *testing.B) {