Add log line for error in segment.

segment.go

@@ -82,10 +82,17 @@ func (l Logger) Segment(pctx context.Context, message string, options ...Option)
 //      }
 //  }
 //
+//It is expected that errors in the returned function are actual problems, as it will log the error. It is not expected
+//that segments will be used where the error is unimportant.
 func (l Logger) SegmentFn(pctx context.Context, message string, options ...Option) func(func(ctx context.Context) error) error {
 	return func(f func(ctx context.Context) error) error {
 		c, done := l.Segment(pctx, message, options...)
+
 		err := f(c)
+		if err != nil {
+			l.Error(c, "segment errored", Err(err))
+		}
+
 		done()
 		return err
 	}

segment_test.go

@@ -81,7 +81,7 @@ func TestLogger_Segment(t *testing.T) {
 func TestLogger_SegmentFn(t *testing.T) {
 	t.Run("starting a segment outputs a message, and closing a segment also outputs a message with fields indicating begin/end, verifies function is called and error returned", func(t *testing.T) {
 		mockImpl := MockImpl{}
-		mockImpl.On("Impl", mock.Anything, mock.Anything).Times(3)
+		mockImpl.On("Impl", mock.Anything, mock.Anything).Times(4)
 
 		expectedMessage := "message"
 		expectedInnerMessage := "inner message"
@@ -97,10 +97,11 @@ func TestLogger_SegmentFn(t *testing.T) {
 		assert.True(t, mockImpl.AssertExpectations(t))
 		assert.Equal(t, io.ErrUnexpectedEOF, err)
 
-		var capturedMessage [3]Message
+		var capturedMessage [4]Message
 		capturedMessage[0] = mockImpl.Calls[0].Arguments.Get(1).(Message)
 		capturedMessage[1] = mockImpl.Calls[1].Arguments.Get(1).(Message)
 		capturedMessage[2] = mockImpl.Calls[2].Arguments.Get(1).(Message)
+		capturedMessage[3] = mockImpl.Calls[3].Arguments.Get(1).(Message)
 
 		assert.Equal(t, expectedMessage, capturedMessage[0].Message)
 		assert.Equal(t, SegmentStartValue, capturedMessage[0].Data[SegmentField])
@@ -109,8 +110,10 @@ func TestLogger_SegmentFn(t *testing.T) {
 		assert.Equal(t, expectedInnerMessage, capturedMessage[1].Message)
 		assert.Equal(t, expectedValue, capturedMessage[1].Data[expectedKey])
 
-		assert.Equal(t, expectedMessage, capturedMessage[2].Message)
-		assert.Equal(t, SegmentEndValue, capturedMessage[2].Data[SegmentField])
-		assert.Equal(t, expectedValue, capturedMessage[2].Data[expectedKey])
+		assert.Contains(t, capturedMessage[2].Message, "segment errored")
+
+		assert.Equal(t, expectedMessage, capturedMessage[3].Message)
+		assert.Equal(t, SegmentEndValue, capturedMessage[3].Data[SegmentField])
+		assert.Equal(t, expectedValue, capturedMessage[3].Data[expectedKey])
 	})
 }