Hi Chris, Christopher Baines writes: > This is part of the following builder script: > > (cons "--enable-mpi-java" #) > > from: /gnu/store/yngxnpcs4s6y8acxf4nwx5pcpj0j6q6i-java-openmpi-4.1.4-builder > > And when attempting to build that derivation, you get the following > error. > > ice-9/read.scm:126:4: In procedure read-expr*: > /gnu/store/yngxnpcs4s6y8acxf4nwx5pcpj0j6q6i-java-openmpi-4.1.4-builder:1:3820: Unknown # object: "#<" > > > It would be nice if Guix could detect this category of problems and > raise an error at the time the derivation is created, rather than the > error occuring only when you build the derivation. > > This would be helpful particularly for the Guix Data Service since > currently it ends up storing these useless derivations, often many times > since the builder includes some often changing string (7f366e0cd930 in > the example above), so this is a common cause of spurious changes > between revisions (as often noted on qa.guix.gnu.org). We could probably modify sexp->string, or the builder bind in gexp->derivation so that the sexp is sanity-checked for non-printable things (we could even work on a whitelist basis). However, the docstring of sexp->string talks about performance, and indeed "write" is pure C code and very fast. I'd be reluctant to introduce a performance hit that would be too heavy here. This particular example though was caused by non-gexp #:phase arguments, so another option could be to sanity check sexps given to sexp->gexp, but again, the docstring talks about performance, so I'm not sure what we should do here. In general, things written only with G-Exps should work well, because you can't insert random stuff into them, but S-Exps are more dangerous, hence why I think this option would be a better middle ground. Paging Ludo wrt. the performance cost of this (I can write a patch for it adding a whitelist of what is allowed in a sexp->gexp sexp). Best, -- Josselin Poiret