Two questions about building GHC from sources

[Norman Ramsey]

 > >  1. If my bootstrap compiler changes (e.g., from 8.10.5 to 9.0.1), is
 > >     Hadrian smart enough to rebuild everything?  If not, how do I
 > >     force it to start over?
 > 
 > (1), I would hope so. If not, that's a bug.

I have confirmed that when the bootstrap compiler changes, Hadrian
cannot successfully rebuild GHC.  Reproducing the fault takes 11
steps, one of which is a full GHC build, so it's a bit time-consuming.
The second build fails with an uncaught exception in Shake.

I've reported the bug as issue #20429.


Norman