[petsc-dev] [petsc-maint] circular dependency [nightlybuilds did not catch]

[Jed Brown]

"Smith, Barry F." <bsmith at mcs.anl.gov> writes:

>> When we are at it, why we sometimes have <class>types.h and sometimes not?
>
>   We add these "as needed"; Jed can explain better exactly when they are needed.

We did some of them to limit header dependencies.  For example:

https://bitbucket.org/petsc/petsc/commits/c619b03e9a39856418a9e23c79aa5be44c20f181

They've been used in other places without doing the follow-up work of
removing the dependency on petscxxx.h in favor of petscxxxtypes.h (which
would be a breaking change for some users, but improve incremental build
times).