UnusedMustUse warnings are emitted after the toolchain ran

[anuejn]

The UnusedMustUse warnings rely on the garbage-collector and are therefore are emitted at the termination of the python script. This is quite unfortunate when one is using nmigen to execute the build plan because one has to wait for the (long-running) toolchain to finish before obvious bugs are pointed out.

[whitequark]

I'm not aware of any way to improve on this in general; in Migen you didn't even have late warnings, you were just left to wonder why your design is broken.

If you find that you stumble on this often, use do_build=False.

[anuejn]

Ok thanks anyways :)