Logger: Add Log method (#1118)

Adds a Logger.Log method which logs a message and fields at the
provided level.

    log.Log(zap.InfoLevel, msg, fields...)
    // is the same as
    log.Info(msg, fields...)

Resolve #1084

logger.go

@@ -190,6 +190,14 @@ func (log *Logger) Check(lvl zapcore.Level, msg string) *zapcore.CheckedEntry {
 	return log.check(lvl, msg)
 }
 
+// Log logs a message at the specified level. The message includes any fields
+// passed at the log site, as well as any fields accumulated on the logger.
+func (log *Logger) Log(lvl zapcore.Level, msg string, fields ...Field) {
+	if ce := log.check(lvl, msg); ce != nil {
+		ce.Write(fields...)
+	}
+}
+
 // Debug logs a message at DebugLevel. The message includes any fields passed
 // at the log site, as well as any fields accumulated on the logger.
 func (log *Logger) Debug(msg string, fields ...Field) {

logger_test.go

@@ -119,7 +119,8 @@ func TestLoggerLogPanic(t *testing.T) {
 		should   bool
 		expected string
 	}{
-		{func(logger *Logger) { logger.Check(PanicLevel, "bar").Write() }, true, "bar"},
+		{func(logger *Logger) { logger.Check(PanicLevel, "foo").Write() }, true, "foo"},
+		{func(logger *Logger) { logger.Log(PanicLevel, "bar") }, true, "bar"},
 		{func(logger *Logger) { logger.Panic("baz") }, true, "baz"},
 	} {
 		withLogger(t, DebugLevel, nil, func(logger *Logger, logs *observer.ObservedLogs) {
@@ -147,7 +148,8 @@ func TestLoggerLogFatal(t *testing.T) {
 		do       func(*Logger)
 		expected string
 	}{
-		{func(logger *Logger) { logger.Check(FatalLevel, "bar").Write() }, "bar"},
+		{func(logger *Logger) { logger.Check(FatalLevel, "foo").Write() }, "foo"},
+		{func(logger *Logger) { logger.Log(FatalLevel, "bar") }, "bar"},
 		{func(logger *Logger) { logger.Fatal("baz") }, "baz"},
 	} {
 		withLogger(t, DebugLevel, nil, func(logger *Logger, logs *observer.ObservedLogs) {
@@ -194,12 +196,36 @@ func TestLoggerLeveledMethods(t *testing.T) {
 	})
 }
 
+func TestLoggerLogLevels(t *testing.T) {
+	withLogger(t, DebugLevel, nil, func(logger *Logger, logs *observer.ObservedLogs) {
+		levels := []zapcore.Level{
+			DebugLevel,
+			InfoLevel,
+			WarnLevel,
+			ErrorLevel,
+			DPanicLevel,
+		}
+		for i, level := range levels {
+			logger.Log(level, "")
+			output := logs.AllUntimed()
+			assert.Equal(t, i+1, len(output), "Unexpected number of logs.")
+			assert.Equal(t, 0, len(output[i].Context), "Unexpected context on first log.")
+			assert.Equal(
+				t,
+				zapcore.Entry{Level: level},
+				output[i].Entry,
+				"Unexpected output from %s-level logger method.", level)
+		}
+	})
+}
+
 func TestLoggerAlwaysPanics(t *testing.T) {
 	// Users can disable writing out panic-level logs, but calls to logger.Panic()
 	// should still call panic().
 	withLogger(t, FatalLevel, nil, func(logger *Logger, logs *observer.ObservedLogs) {
 		msg := "Even if output is disabled, logger.Panic should always panic."
 		assert.Panics(t, func() { logger.Panic("foo") }, msg)
+		assert.Panics(t, func() { logger.Log(PanicLevel, "foo") }, msg)
 		assert.Panics(t, func() {
 			if ce := logger.Check(PanicLevel, "foo"); ce != nil {
 				ce.Write()
@@ -216,6 +242,9 @@ func TestLoggerAlwaysFatals(t *testing.T) {
 		stub := exit.WithStub(func() { logger.Fatal("") })
 		assert.True(t, stub.Exited, "Expected calls to logger.Fatal to terminate process.")
 
+		stub = exit.WithStub(func() { logger.Log(FatalLevel, "") })
+		assert.True(t, stub.Exited, "Expected calls to logger.Fatal to terminate process.")
+
 		stub = exit.WithStub(func() {
 			if ce := logger.Check(FatalLevel, ""); ce != nil {
 				ce.Write()