About behavior changes for thumbnail/transformer that callback data is nil

[dreampiggy]

Background

In 5.14.0, SDWebImage change the behavior that if you use Transformer (via SDImageTransformer) or Thumbnail Decoding (via SDImageCoderThumbnailPixelSize), the SDWebImageManager's completedBlock will callback nil data.

In old version (5.13.2), this has the following behavior:

1. If image was from downloaded data, the thumbnail case will callback the downloaded data. The transformer case will callback the new encoded data (from transformed image)
2. If image was from disk cache, the thumbnail case will callback the full size data. The transformer case will callback the new encoded data (from transformed image)
3. If image was from memory cache, all the case that the callback data is nil (by defaults)

I think these 3 cases are so confusing, because as a user, when I use transformer, the callback data always match my transformed image. But when I use thumbnail decoding, the callback data is full size image data but not my smaller thumbnail size representation. Because we supports the ResizeTransformer to small down, why these similar things has different behavior ?

So during the changes #3423 to revert the old hack, I deceide to ignore the cache data at all. Because actually both thunbmail and transformer, there are 2 kind2 of image (processed one and original one) and 2 kinds of data (new image encoded data and original data).

Discussion

Is this change suitable for your real world Application ? Should I use some control option for this behavior changes, or need any feedback from your testing result ?