examples don't run in the source tree anymore

I know this was done on purpose, but it doesn't make sense. Any examples which consist of just a plugin and some QML are now very hard to run, e.g.

$ cd ~/dev/qt59/qtdeclarative/examples/quick/imageprovider
$ qmake
Info: creating stash file /Users/rutledge/dev/qt59/qtdeclarative/.qmake.stash
Project ERROR: You cannot build examples inside the Qt source tree, except as part of a proper Qt build.

So what is a user supposed to do, copy the whole example to /tmp first, to be able to build in the same location where the source is?

It's a really heavy-handed, unfriendly rule. My guess is it is in place to prevent the build system from getting confused when some build artifacts are left behind in example dirs, on the assumption that everyone should be doing shadow builds by default, so the source dirs should always be clean. But some examples are not set up for shadow builds. And requiring every example to have a main.cpp is also wrong, IMO.