SudokuBlocks.app from one year ago will not run on macOS Sierra. Aggravating, but there it is. So I decided to upgrade the app to Swift3.
This was a bit of a challenge. The biggest thing is that automatic code migration didn't appear to work well at first, and also Xcode was complaining about some project settings, which I didn't know how to make right.
I made a brand new project, set up new xib files, and then added the old Swift files to it. I did this in two phases, in the first one there was just enough of the code to load a puzzle and draw it on the screen.
I tried to build the project and then fixed the errors one by one. I probably had 50 errors in phase 1 and 100 in phase 2. Xcode was really good at telling me what was wrong and often making the fix as simple as a double-click.
I ran into an additional bug where the view would not update properly, but I solved that.
[Since then I have tried again with letting Xcode try to fix the project, and it worked a lot better. I got the app to the state where it would run in about 20 minutes versus most of a day to rebuild it from scratch.]