ctx: store logger in context when missing or different that stored one

Current implementation stores a copy of the logger as a pointer and
update its content, which is now unecessary since the introduction of
WithContext.

The new WithContext now takes the pointer and store it in the context if
none is stored already or if the last one stored is a different pointer.
This way it is still possible to update the context of a logger stored
in the context, but it is also possible to store a copy of the logger in
a sub-context.

Fix #80

ctx.go

@@ -2,38 +2,39 @@ package zerolog
 
 import (
 	"context"
-	"io/ioutil"
 )
 
 var disabledLogger *Logger
 
 func init() {
-	l := New(ioutil.Discard).Level(Disabled)
+	l := Nop()
 	disabledLogger = &l
 }
 
 type ctxKey struct{}
 
 // WithContext returns a copy of ctx with l associated. If an instance of Logger
-// is already in the context, the pointer to this logger is updated with l.
+// is already in the context, the context is not updated.
 //
 // For instance, to add a field to an existing logger in the context, use this
 // notation:
 //
 //     ctx := r.Context()
 //     l := zerolog.Ctx(ctx)
-//     ctx = l.With().Str("foo", "bar").WithContext(ctx)
-func (l Logger) WithContext(ctx context.Context) context.Context {
+//     l.UpdateContext(func(c Context) Context {
+//         return c.Str("bar", "baz")
+//     })
+func (l *Logger) WithContext(ctx context.Context) context.Context {
 	if lp, ok := ctx.Value(ctxKey{}).(*Logger); ok {
-		// Update existing pointer.
-		*lp = l
+		if lp == l {
+			// Do not store same logger.
 			return ctx
 		}
-	if l.level == Disabled {
+	} else if l.level == Disabled {
 		// Do not store disabled logger.
 		return ctx
 	}
-	return context.WithValue(ctx, ctxKey{}, &l)
+	return context.WithValue(ctx, ctxKey{}, l)
 }
 
 // Ctx returns the Logger associated with the ctx. If no logger

ctx_test.go

@@ -30,18 +30,34 @@ func TestCtx(t *testing.T) {
 }
 
 func TestCtxDisabled(t *testing.T) {
-	ctx := disabledLogger.WithContext(context.Background())
+	dl := New(ioutil.Discard).Level(Disabled)
+	ctx := dl.WithContext(context.Background())
 	if ctx != context.Background() {
 		t.Error("WithContext stored a disabled logger")
 	}
 
-	ctx = New(ioutil.Discard).WithContext(ctx)
-	if reflect.DeepEqual(Ctx(ctx), disabledLogger) {
+	l := New(ioutil.Discard).With().Str("foo", "bar").Logger()
+	ctx = l.WithContext(ctx)
+	if Ctx(ctx) != &l {
 		t.Error("WithContext did not store logger")
 	}
 
-	ctx = disabledLogger.WithContext(ctx)
-	if !reflect.DeepEqual(Ctx(ctx), disabledLogger) {
-		t.Error("WithContext did not update logger pointer with disabled logger")
+	l.UpdateContext(func(c Context) Context {
+		return c.Str("bar", "baz")
+	})
+	ctx = l.WithContext(ctx)
+	if Ctx(ctx) != &l {
+		t.Error("WithContext did not store updated logger")
+	}
+
+	l = l.Level(DebugLevel)
+	ctx = l.WithContext(ctx)
+	if Ctx(ctx) != &l {
+		t.Error("WithContext did not store copied logger")
+	}
+
+	ctx = dl.WithContext(ctx)
+	if Ctx(ctx) != &dl {
+		t.Error("WithContext did not overide logger with a disabled logger")
 	}
 }