Add color-aware LevelEncoders

Use the internal package to add small, colored LevelEncoders. For safety (since
we don't check that the output is a TTY), keep the default uncolored.

zapcore/encoder.go

@@ -21,7 +21,6 @@
 package zapcore
 
 import (
-	"strings"
 	"time"
 
 	"go.uber.org/zap/buffer"
@@ -36,18 +35,44 @@ func LowercaseLevelEncoder(l Level, enc PrimitiveArrayEncoder) {
 	enc.AppendString(l.String())
 }
 
+// LowercaseColorLevelEncoder serializes a Level to a lowercase string and adds coloring.
+// For example, InfoLevel is serialized to "info" and colored blue.
+func LowercaseColorLevelEncoder(l Level, enc PrimitiveArrayEncoder) {
+	s, ok := _levelToLowercaseColorString[l]
+	if !ok {
+		s = _unknownLevelColor.Add(l.String())
+	}
+	enc.AppendString(s)
+}
+
 // CapitalLevelEncoder serializes a Level to an all-caps string. For example,
 // InfoLevel is serialized to "INFO".
 func CapitalLevelEncoder(l Level, enc PrimitiveArrayEncoder) {
-	enc.AppendString(strings.ToUpper(l.String()))
+	enc.AppendString(l.CapitalString())
+}
+
+// CapitalColorLevelEncoder serializes a Level to an all-caps string and adds color.
+// For example, InfoLevel is serialized to "INFO" and colored blue.
+func CapitalColorLevelEncoder(l Level, enc PrimitiveArrayEncoder) {
+	s, ok := _levelToCapitalColorString[l]
+	if !ok {
+		s = _unknownLevelColor.Add(l.CapitalString())
+	}
+	enc.AppendString(s)
 }
 
 // UnmarshalText unmarshals text to a LevelEncoder. "capital" is unmarshaled to
-// CapitalLevelEncoder, and anything else is unmarshaled to LowercaseLevelEncoder.
+// CapitalLevelEncoder, "coloredCapital" is unmarshaled to CapitalColorLevelEncoder,
+// "colored" is unmarshaled to LowercaseColorLevelEncoder, and anything else
+// is unmarshaled to LowercaseLevelEncoder.
 func (e *LevelEncoder) UnmarshalText(text []byte) error {
 	switch string(text) {
 	case "capital":
 		*e = CapitalLevelEncoder
+	case "capitalColor":
+		*e = CapitalColorLevelEncoder
+	case "color":
+		*e = LowercaseColorLevelEncoder
 	default:
 		*e = LowercaseLevelEncoder
 	}

zapcore/level.go

@@ -76,6 +76,30 @@ func (l Level) String() string {
 	}
 }
 
+// CapitalString returns an all-caps ASCII representation of the log level.
+func (l Level) CapitalString() string {
+	// Printing levels in all-caps is common enough that we should export this
+	// functionality.
+	switch l {
+	case DebugLevel:
+		return "DEBUG"
+	case InfoLevel:
+		return "INFO"
+	case WarnLevel:
+		return "WARN"
+	case ErrorLevel:
+		return "ERROR"
+	case DPanicLevel:
+		return "DPANIC"
+	case PanicLevel:
+		return "PANIC"
+	case FatalLevel:
+		return "FATAL"
+	default:
+		return fmt.Sprintf("LEVEL(%d)", l)
+	}
+}
+
 // MarshalText marshals the Level to text. Note that the text representation
 // drops the -Level suffix (see example).
 func (l *Level) MarshalText() ([]byte, error) {

zapcore/level_strings.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2016 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 "go.uber.org/zap/internal/color"
+
+var (
+	_levelToColor = map[Level]color.Color{
+		DebugLevel:  color.Magenta,
+		InfoLevel:   color.Blue,
+		WarnLevel:   color.Yellow,
+		ErrorLevel:  color.Red,
+		DPanicLevel: color.Red,
+		PanicLevel:  color.Red,
+		FatalLevel:  color.Red,
+	}
+	_unknownLevelColor = color.Red
+
+	_levelToLowercaseColorString = make(map[Level]string, len(_levelToColor))
+	_levelToCapitalColorString   = make(map[Level]string, len(_levelToColor))
+)
+
+func init() {
+	for level, color := range _levelToColor {
+		_levelToLowercaseColorString[level] = color.Add(level.String())
+		_levelToCapitalColorString[level] = color.Add(level.CapitalString())
+	}
+}

zapcore/level_strings_test.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2016 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 (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAllLevelsCoveredByLevelString(t *testing.T) {
+	numLevels := int((_maxLevel - _minLevel) + 1)
+
+	isComplete := func(m map[Level]string) bool {
+		return len(m) == numLevels
+	}
+
+	assert.True(t, isComplete(_levelToLowercaseColorString), "Colored lowercase strings don't cover all levels.")
+	assert.True(t, isComplete(_levelToCapitalColorString), "Colored capital strings don't cover all levels.")
+}

zapcore/level_test.go

@@ -42,7 +42,8 @@ func TestLevelString(t *testing.T) {
 	}
 
 	for lvl, stringLevel := range tests {
-		assert.Equal(t, stringLevel, lvl.String())
+		assert.Equal(t, stringLevel, lvl.String(), "Unexpected lowercase level string.")
+		assert.Equal(t, strings.ToUpper(stringLevel), lvl.CapitalString(), "Unexpected all-caps level string.")
 	}
 }