[petsc-dev] Undefined symbols for _kspfgmresmodifypcksp_ and _kspfgmresmodifypcnochange_ when rebuilding

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> Someone changes an interface, and you pull the change. The header changes
> will cause all the C files
> using that API to rebuild. However, the doc system (sowing) runs bfort on
> the C file to generate the Fortran
> binding. It runs on all headers at once, so there is no separately rule for
> bforting a C file when it changes.
> Things are now even worse, since we have Python code separate from bfort
> which create the Fortran
> modules, which also will not fire on updates to the C file.
>
> The simplest fix is that you know that every time you see this problem, you
> rerun 'make allfortranstubs'.
> The complicate fix is to rewrite bfort and the module generation into one
> program which respects the
> dependency information. 

A simpler solution that is not a sledgehammer would be for these
"generate everything" scripts write a temporary file, diff with the
(possibly stale) existing output, and only replaces when the content is
different.  We don't want to make allfortranstubs always because it
implies that every ftn-auto file will be recompiled even if it hasn't
changed.  That is faster with ccache, but still not fast enough (and
implies re-linking everything).

> Since there is literally no credit associated with this job, it is
> unlikely ever to happen.  We await the passing of the last Fortran
> programmer.