Allow derivations in meta

[Ekleog]

It looks like nix refuses to have derivations in meta for some operations (eg. exporting as JSON):

nix/src/libexpr/get-drvs.cc

Line 166 in 6924bdf

bool DrvInfo::checkMeta(Value & v)

This has caused NixOS/nixpkgs#50230, after the change in NixOS/nixpkgs#44439.

Currently, the solution appears to be to use passthru.tests instead of meta.tests, which is a possibility but appears semantically wrong.

Would it be possible to make Nix able to have derivations in meta? I think a legitimate display value for these would be the result of instantiating the derivation, without building it.

Alternatively, I think checkMeta should be called at each build, so that it's not possible to miss it like we did :)

[edolstra]

meta is really not intended for this. It's a list of name/value pairs for use by nix-env. Indeed passthru should be used instead.

[Ekleog]

It's indeed the workaround implemented in NixOS/nixpkgs#50233, but it feels (at least to me) semantically wrong.

Then, if meta is to stay a list of stringifyable things only, I guess it'd be useful to make sure such breakage can't fly under the radar again, eg. by making building a derivation run checkMeta on it?

[edolstra]

Doesn't make-tarball.nix in Nixpkgs already catch this?

[grahamc]

I’m also surprised ofborg did not catch this

…

On Nov 12, 2018, at 11:02, Eelco Dolstra ***@***.***> wrote: Doesn't make-tarball.nix in Nixpkgs already catch this? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

[Ekleog]

For make-tarball.nix I don't really know but it appears it passed. As for ofborg I think it passed because the check-meta.nix had been adapted to accept derivations, and ofborg didn't expect nix to perform additional checks on meta in some cases more than the people who had reviewed the original RFC?

[JohnAZoidberg]

Is the conclusion to use passthru instead or do we want to further discuss it?

[domenkozar]

The former :) It would be good to document this better though.

[stale]

I marked this as stale due to inactivity. → More info

[stale]

I closed this issue due to inactivity. → More info