Config: Validate Level and EncoderConfig (uber-go#791)

This adds validation for Level and EncoderConfig.EncoderTime when
building a logger from a zap.Config.

Resolves uber-go#777

Co-authored-by: Abhinav Gupta <abg@uber.com>

config.go

@@ -21,6 +21,7 @@
 package zap
 
 import (
+	"fmt"
 	"sort"
 	"time"
 
@@ -174,6 +175,10 @@ func (cfg Config) Build(opts ...Option) (*Logger, error) {
 		return nil, err
 	}
 
+	if cfg.Level == (AtomicLevel{}) {
+		return nil, fmt.Errorf("missing Level")
+	}
+
 	log := New(
 		zapcore.NewCore(enc, sink, cfg.Level),
 		cfg.buildOptions(errSink)...,

config_test.go

@@ -27,6 +27,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zapcore"
 )
 
 func TestConfig(t *testing.T) {
@@ -106,3 +107,40 @@ func TestConfigWithInvalidPaths(t *testing.T) {
 		})
 	}
 }
+
+func TestConfigWithMissingAttributes(t *testing.T) {
+	tests := []struct {
+		desc      string
+		cfg       Config
+		expectErr string
+	}{
+		{
+			desc: "missing level",
+			cfg: Config{
+				Encoding: "json",
+			},
+			expectErr: "missing Level",
+		},
+		{
+			desc: "missing encoder time in encoder config",
+			cfg: Config{
+				Level:    NewAtomicLevelAt(zapcore.InfoLevel),
+				Encoding: "json",
+				EncoderConfig: zapcore.EncoderConfig{
+					MessageKey: "msg",
+					TimeKey:    "ts",
+				},
+			},
+			expectErr: "missing EncodeTime in EncoderConfig",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			cfg := tt.cfg
+			_, err := cfg.Build()
+			require.Error(t, err)
+			assert.Equal(t, tt.expectErr, err.Error())
+		})
+	}
+}

encoder.go

@@ -62,6 +62,10 @@ func RegisterEncoder(name string, constructor func(zapcore.EncoderConfig) (zapco
 }
 
 func newEncoder(name string, encoderConfig zapcore.EncoderConfig) (zapcore.Encoder, error) {
+	if encoderConfig.TimeKey != "" && encoderConfig.EncodeTime == nil {
+		return nil, fmt.Errorf("missing EncodeTime in EncoderConfig")
+	}
+
 	_encoderMutex.RLock()
 	defer _encoderMutex.RUnlock()
 	if name == "" {