watch for multiple errors

sugar.go

@@ -31,6 +31,7 @@ import (
 const (
 	_oddNumberErrMsg    = "Ignored key without a value."
 	_nonStringKeyErrMsg = "Ignored key-value pairs with non-string keys."
+	_multipleErrMsg     = "Multiple errors without a key."
 )
 
 // A SugaredLogger wraps the base Logger functionality in a slower, but less
@@ -340,6 +341,7 @@ func (s *SugaredLogger) sweetenFields(args []interface{}) []Field {
 	// fields, we shouldn't penalize them with extra allocations.
 	fields := make([]Field, 0, len(args))
 	var invalid invalidPairs
+	var seenError bool
 
 	for i := 0; i < len(args); {
 		// This is a strongly-typed field. Consume it and move on.
@@ -351,7 +353,12 @@ func (s *SugaredLogger) sweetenFields(args []interface{}) []Field {
 
 		// If it is an error, consume it and move on.
 		if err, ok := args[i].(error); ok {
-			fields = append(fields, Error(err))
+			if !seenError {
+				seenError = true
+				fields = append(fields, Error(err))
+			} else {
+				s.base.Error(_multipleErrMsg, Error(err))
+			}
 			i++
 			continue
 		}

sugar_test.go

@@ -47,6 +47,12 @@ func TestSugarWith(t *testing.T) {
 			Context: []Field{Array("invalid", invalidPairs(pairs))},
 		}
 	}
+	ignoredError := func(err error) observer.LoggedEntry {
+		return observer.LoggedEntry{
+			Entry:   zapcore.Entry{Level: ErrorLevel, Message: _multipleErrMsg},
+			Context: []Field{Error(err)},
+		}
+	}
 
 	tests := []struct {
 		desc     string
@@ -123,6 +129,15 @@ func TestSugarWith(t *testing.T) {
 				nonString(invalidPair{2, true, "bar"}, invalidPair{5, 42, "reversed"}),
 			},
 		},
+		{
+			desc:     "multiple errors",
+			args:     []interface{}{errors.New("first"), errors.New("second"), errors.New("third")},
+			expected: []Field{Error(errors.New("first"))},
+			errLogs: []observer.LoggedEntry{
+				ignoredError(errors.New("second")),
+				ignoredError(errors.New("third")),
+			},
+		},
 	}
 
 	for _, tt := range tests {