[log] implement NewErrorLogger

New function allows simpler creation of logging function with arbitrary
loglevel.

Change-Id: Ic47f50f87daa4001112f7883ee7d672048311097

Author: xobotyi

logger/logger.go

@@ -3,6 +3,7 @@ package logger
 import (
 	"math"
 
+	"dev.gaijin.team/go/golib/e"
 	"dev.gaijin.team/go/golib/fields"
 )
 
@@ -171,3 +172,14 @@ func (l Logger) Flush() error {
 func (l Logger) IsZero() bool {
 	return l.adapter == nil && l.maxLevel == 0
 }
+
+// NewErrorLogger creates new [e.ErrorLogger] that allows to log errors with
+// given log-level.
+//
+// The function is most usesful for scenarios where loglevel is configured after
+// logger creation, such as in a middlewares.
+func NewErrorLogger(log Logger, level int) e.ErrorLogger {
+	return func(msg string, err error, fs ...fields.Field) {
+		log.Log(level, msg, err, fs...)
+	}
+}

logger/zapadapter/adapter_test.go

@@ -122,4 +122,20 @@ func TestAdapter(t *testing.T) {
 
 		assert.Equal(t, "test-logger", logs.All()[0].LoggerName)
 	})
+
+	t.Run("NewErrorLogger()", func(t *testing.T) {
+		t.Parallel()
+
+		adapter, logs := newAdapter()
+		lgr := logger.New(adapter, logger.LevelError)
+		errorLogger := logger.NewErrorLogger(lgr, logger.LevelError)
+
+		errorLogger("test", errors.New("test"))
+
+		require.Equal(t, 1, logs.Len())
+
+		assert.Equal(t, zapcore.ErrorLevel, logs.All()[0].Level)
+		assert.Equal(t, "test", logs.All()[0].Message)
+		assert.Equal(t, "test", logs.All()[0].ContextMap()["error"])
+	})
 }