This reminds me that PETSc's build system is tied to PETSC_ARCH, thus does not support a read-only source tree. To do this, we would have to make tests and Fortran stubs go into the build directory (we want that already) and to lessen our dependence on PETSC_ARCH. I think we should be able to make it possible to run /path/to/petsc/configure with no special arguments and have it set up a normal out-of-source build that would be independent of PETSC_DIR and PETSC_ARCH. If instead, you run configure from PETSC_DIR, it would continue to use PETSC_ARCH as the build directory. (To make these otherwise uniform, PETSC_ARCH would probably become just a hint to run make from the appropriate directory.) Any reason we should not do this once the testing and Fortran stuff works that way?