Add option to increase the level of a logger (#775)

We've had a few requests on how to change the level of a logger. With
the current APIs, it's not possible to reduce the log level (e.g., go
from Info to Debug), but it is possible to increase the level using
`WrapCore` with a custom filtering core.

Since it's a common request, I think we should add an option to make
this easy to use.

I want to make sure "increase" is part of the API to avoid confusion on
whether it can reduce the log level.

Fixes #774.

increase_level_test.go

@@ -0,0 +1,85 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zap
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest/observer"
+)
+
+func newLoggedEntry(level zapcore.Level, msg string) observer.LoggedEntry {
+	return observer.LoggedEntry{
+		Entry:   zapcore.Entry{Level: level, Message: msg},
+		Context: []zapcore.Field{},
+	}
+}
+
+func TestIncreaseLevelTryDecrease(t *testing.T) {
+	errorOut := &bytes.Buffer{}
+	opts := []Option{
+		ErrorOutput(zapcore.AddSync(errorOut)),
+	}
+	withLogger(t, WarnLevel, opts, func(logger *Logger, logs *observer.ObservedLogs) {
+		logger.Warn("original warn log")
+
+		debugLogger := logger.WithOptions(IncreaseLevel(DebugLevel))
+		debugLogger.Debug("ignored debug log")
+		debugLogger.Warn("increase level warn log")
+		debugLogger.Error("increase level error log")
+
+		assert.Equal(t, []observer.LoggedEntry{
+			newLoggedEntry(WarnLevel, "original warn log"),
+			newLoggedEntry(WarnLevel, "increase level warn log"),
+			newLoggedEntry(ErrorLevel, "increase level error log"),
+		}, logs.AllUntimed(), "unexpected logs")
+		assert.Equal(t,
+			`failed to IncreaseLevel: invalid increase level, as level "info" is allowed by increased level, but not by existing core`,
+			errorOut.String(),
+			"unexpected error output",
+		)
+	})
+}
+
+func TestIncreaseLevel(t *testing.T) {
+	errorOut := &bytes.Buffer{}
+	opts := []Option{
+		ErrorOutput(zapcore.AddSync(errorOut)),
+	}
+	withLogger(t, WarnLevel, opts, func(logger *Logger, logs *observer.ObservedLogs) {
+		logger.Warn("original warn log")
+
+		errorLogger := logger.WithOptions(IncreaseLevel(ErrorLevel))
+		errorLogger.Debug("ignored debug log")
+		errorLogger.Warn("ignored warn log")
+		errorLogger.Error("increase level error log")
+
+		assert.Equal(t, []observer.LoggedEntry{
+			newLoggedEntry(WarnLevel, "original warn log"),
+			newLoggedEntry(ErrorLevel, "increase level error log"),
+		}, logs.AllUntimed(), "unexpected logs")
+
+		assert.Empty(t, errorOut.String(), "expect no error output")
+	})
+}

logger_test.go

@@ -392,6 +392,21 @@ func TestLoggerReplaceCore(t *testing.T) {
 	})
 }
 
+func TestLoggerIncreaseLevel(t *testing.T) {
+	withLogger(t, DebugLevel, opts(IncreaseLevel(WarnLevel)), func(logger *Logger, logs *observer.ObservedLogs) {
+		logger.Info("logger.Info")
+		logger.Warn("logger.Warn")
+		logger.Error("logger.Error")
+		require.Equal(t, 2, logs.Len(), "expected only warn + error logs due to IncreaseLevel.")
+		assert.Equal(
+			t,
+			logs.AllUntimed()[0].Entry.Message,
+			"logger.Warn",
+			"Expected first logged message to be warn level message",
+		)
+	})
+}
+
 func TestLoggerHooks(t *testing.T) {
 	hook, seen := makeCountingHook()
 	withLogger(t, DebugLevel, opts(Hooks(hook)), func(logger *Logger, logs *observer.ObservedLogs) {

options.go

@@ -20,7 +20,11 @@
 
 package zap
 
-import "go.uber.org/zap/zapcore"
+import (
+	"fmt"
+
+	"go.uber.org/zap/zapcore"
+)
 
 // An Option configures a Logger.
 type Option interface {
@@ -107,3 +111,16 @@ func AddStacktrace(lvl zapcore.LevelEnabler) Option {
 		log.addStack = lvl
 	})
 }
+
+// IncreaseLevel increase the level of the logger. It has no effect if
+// the passed in level tries to decrease the level of the logger.
+func IncreaseLevel(lvl zapcore.LevelEnabler) Option {
+	return optionFunc(func(log *Logger) {
+		core, err := zapcore.NewIncreaseLevelCore(log.core, lvl)
+		if err != nil {
+			fmt.Fprintf(log.errorOutput, "failed to IncreaseLevel: %v", err)
+		} else {
+			log.core = core
+		}
+	})
+}

zapcore/increase_level.go

@@ -0,0 +1,55 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zapcore
+
+import "fmt"
+
+type levelFilterCore struct {
+	Core
+
+	level LevelEnabler
+}
+
+// NewIncreaseLevelCore creates a core that can be used to increase the level of
+// an existing Core. It cannot be used to decrease the logging level, as it acts
+// as a filter before calling the underlying core. If level decreases the log level,
+// an error is returned.
+func NewIncreaseLevelCore(core Core, level LevelEnabler) (Core, error) {
+	for l := _maxLevel; l >= _minLevel; l-- {
+		if !core.Enabled(l) && level.Enabled(l) {
+			return nil, fmt.Errorf("invalid increase level, as level %q is allowed by increased level, but not by existing core", l)
+		}
+	}
+
+	return &levelFilterCore{core, level}, nil
+}
+
+func (c *levelFilterCore) Enabled(lvl Level) bool {
+	return c.level.Enabled(lvl)
+}
+
+func (c *levelFilterCore) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
+	if !c.Enabled(ent.Level) {
+		return ce
+	}
+
+	return c.Core.Check(ent, ce)
+}

zapcore/increase_level_test.go

@@ -0,0 +1,101 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zapcore_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	. "go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest/observer"
+)
+
+func TestIncreaseLevel(t *testing.T) {
+	tests := []struct {
+		coreLevel     Level
+		increaseLevel Level
+		wantErr       bool
+	}{
+		{
+			coreLevel:     InfoLevel,
+			increaseLevel: DebugLevel,
+			wantErr:       true,
+		},
+		{
+			coreLevel:     InfoLevel,
+			increaseLevel: InfoLevel,
+		},
+		{
+			coreLevel:     InfoLevel,
+			increaseLevel: ErrorLevel,
+		},
+		{
+			coreLevel:     ErrorLevel,
+			increaseLevel: DebugLevel,
+			wantErr:       true,
+		},
+		{
+			coreLevel:     ErrorLevel,
+			increaseLevel: InfoLevel,
+			wantErr:       true,
+		},
+		{
+			coreLevel:     ErrorLevel,
+			increaseLevel: WarnLevel,
+			wantErr:       true,
+		},
+		{
+			coreLevel:     ErrorLevel,
+			increaseLevel: PanicLevel,
+		},
+	}
+
+	for _, tt := range tests {
+		msg := fmt.Sprintf("increase %v to %v", tt.coreLevel, tt.increaseLevel)
+		t.Run(msg, func(t *testing.T) {
+			logger, _ := observer.New(tt.coreLevel)
+
+			filteredLogger, err := NewIncreaseLevelCore(logger, tt.increaseLevel)
+			if tt.wantErr {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), "invalid increase level")
+				return
+			}
+
+			require.NoError(t, err)
+
+			for l := DebugLevel; l <= FatalLevel; l++ {
+				enabled := filteredLogger.Enabled(l)
+				ce := filteredLogger.Check(Entry{Level: l}, nil)
+
+				if l >= tt.increaseLevel {
+					assert.True(t, enabled, "expect %v to be enabled", l)
+					assert.NotNil(t, ce, "expect non-nil Check")
+				} else {
+					assert.False(t, enabled, "expect %v to be disabled", l)
+					assert.Nil(t, ce, "expect nil Check")
+				}
+			}
+		})
+	}
+}