bug#36207: Circular dependency in gnu/services: mcron -> base -> admin -> mcron

bug#36207: Circular dependency in gnu/services: mcron -> base -> admin -> mcron

[Jack Hill]

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Hi Guix,

As discussed on IRC with Ludo’ and Ricardo, 
4252dace19945f56192477e8cb07973c20a526ba introduced a circular dependency 
among gnu/services modules, by adding a dependency between from base -> 
admin, resulting in the full dependency chain:

  mcron -> base -> admin -> mcron

I ran into this when building a channel. The error reported by guix pull 
was:

```
(repl-version 0 0)
(exception misc-error (value #f) (value "Unbound variable: ~s") (value (mcron-service-type)) (value #f))
```

Ludo’ determined the full error was:

```
gnu/services/admin.scm:161:21: Unbound variable: mcron-service-type
```

by running the repl directly:

```
echo '(primitive-load "/gnu/store/vf892np8mnh2zx9dppcv9k25xk648n2d-inferior-script.scm")' \
| "/gnu/store/j7vxgnaqwimrzsnd8zhq9x1jdp7afl0s-guix-ca45da9fc/bin/guix" "repl"
```

Options for solving this problem include moving the guix-publish service 
into another module. However, this would break the API of (gnu service base),
so we should be careful when doing that.

It doesn't look like guix-publish is used elsewhere in the Guix code 
proper currently.

For now, we might want to revert 4252dace19945f56192477e8cb07973c20a526ba.

Best,
Jack

bug#36207: Circular dependency in gnu/services: mcron -> base -> admin -> mcron

[Ludovic Courtès]

Hi Jack,

Jack Hill <jackhill@jackhill.us> skribis:

> As discussed on IRC with Ludo’ and Ricardo,
> 4252dace19945f56192477e8cb07973c20a526ba introduced a circular
> dependency among gnu/services modules, by adding a dependency between
> from base -> 
> admin, resulting in the full dependency chain:
>
>  mcron -> base -> admin -> mcron
>
> I ran into this when building a channel. The error reported by guix
> pull was:
>
> ```
> (repl-version 0 0)
> (exception misc-error (value #f) (value "Unbound variable: ~s") (value (mcron-service-type)) (value #f))
> ```

This is fixed (surprisingly easily!) by commit
f3d797005374e5333c7596fe86b4a524ab1b9b11.

Let me know if you notice anything wrong!

Thanks for the bug report,
Ludo’.

bug#36207: Circular dependency in gnu/services: mcron -> base -> admin -> mcron

[Jack Hill]

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On Sat, 15 Jun 2019, Ludovic Courtès wrote:

> This is fixed (surprisingly easily!) by commit
> f3d797005374e5333c7596fe86b4a524ab1b9b11.

Neat!

> Let me know if you notice anything wrong!

Everything looks good and works well for me.

> Thanks for the bug report,

Thanks for the quick fix.

Best,
Jack