Handle Hydra evaluation errors gracefully

[domenkozar]

Currently there are two problems that occur if a package fails to evaluate (on purpose):

a) "broken" or "disabled" package is not propagated to reverse dependencies. If a package A depends on package B and B is marked as broken/disabled,
package A will still be evaluate-able and will result in an evaluation error

b) evaluation errors spams the hydra error tab page

---

Proposal to fix b)

• provide high-level throw function that prefixes the error message with something that will indicate the error is supposed to happen
• document the function
• make sure Python and meta.broken uses it
• handle such errors in pkgs/top-level/release-lib.nix by regexing them out from the output

Previous discussions:

• http://lists.science.uu.nl/pipermail/nix-dev/2015-February/016381.html
• b653e3f

[zimbatm]

It's still an issue right ?

[joachifm]

Looks like it

[zimbatm]

It's not the same but similar to madjar/nox#40. It would be nice to have a function that filters out all the invalid builds recursively from a set.

[Profpatsch]

@domenkozar iirc this discussion moved to other issues, would it bother you closing this instance?

[stale]

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