proposal: make build failures explicit results in the store

[Florian Paul Schmidt]

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Hi,

currently I'm trying my hands on building _all_ available packages on
the x86_64 platform in a qemu-vm (with the intended aim to later
publish them to maybe take some load off hydra), but I came across an
issue that might have an easy solution but I'm not sure exactly what's
the right way to proceed.

Basically what I did right now was this:

for n in `guix package -A | cut -f1`; do guix build --no-substitutes\
- --max-silent-time=10 "$n" || true; done

Watching it run I noticed something though: Some package, let's call
it "foo1", seemed to have package "bar" as depencency (the concrete
example for bar was Qt5 which is probably why I noticed ;)), but the
bar build failed. So building foo1 failed, too. So far so good, aside
from foo1's and bar's failure everything is fine.

Now another package, foo2, comes along and it, too, depends on bar.
Since bar failed to build previously guix thinks it's a swell idea to
retry building bar. This, of course, is silly, and in this concrete
example, Qt5, a massive waste of cpu cycles and the only good thing it
does is to bring the universe closer to the heat death.

Afaict the real problem is that the functional approach is slightly
broken here (being functional is fine, just the implementation is
broken). The attempt to build bar _had_ a result. That result was a
build failure and as such it should be explicitly represented in the
store such that when another attempt to build bar comes along, the
result is already known: build failure. And this should make the build
of foo2 fail immediately, too, since one of its dependencies failed to
build.

Once the package definition of bar changes, there's a new store path
for its result and the build will be retried.

Do I miss something here? What do you think?

Have fun,
Flo

- -- 
https://fps.io
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