Request: maintain build time db

[wmertens]

For each attribute, maintain how long it takes to build.

Then, for builds, automatically do dependent attribute builds if they won't take too long (eg < 2 mins)

[Mic92]

I thought about having a black list in nix-review too.

[timokau]

It might even make sense to implement this on the nix level. I've already wanted to ask nix how long a build took several times.

ofBorg could then print something like

The following reverse dependencies were not tested because they exceed the current build capacity:

• chromium (estimated build-time: forever)
• gcc (estimated build-time: 42d)

And nag the contributor to at least test it locally.