bug#25242: Cannot build source derivations with a custom TMPDIR

[Leo Famulari <leo@famulari.name>]

On Wed, Dec 21, 2016 at 10:20:20AM +0100, Ludovic Courtès wrote:
> AFAICS the flaw is that there’s one place where I wrote:
> 
>   if (useChroot && !isBuiltin(drv))
> 
> while several other places just do something like:
> 
>   if (useChroot)
> 
> Could the patch below solve the problem?
> 

> diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
> index e823001..38048ce 100644
> --- a/nix/libstore/build.cc
> +++ b/nix/libstore/build.cc
> @@ -1680,7 +1680,11 @@ void DerivationGoal::startBuilder()
>              % drv.platform % settings.thisSystem % drvPath);
>      }
>  
> -    useChroot = settings.useChroot;
> +    /* Note: built-in builders are *not* running in a chroot environment so
> +       that we can easily implement them in Guile without having it as a
> +       derivation input (they are running under a separate build user,
> +       though).  */
> +    useChroot = settings.useChroot && !isBuiltin(drv);
>  
>      /* Construct the environment passed to the builder. */
>      env.clear();
> @@ -2048,12 +2052,7 @@ void DerivationGoal::runChild()
>          commonChildInit(builderOut);
>  
>  #if CHROOT_ENABLED
> -	/* Note: built-in builders are *not* running in a chroot environment
> -	   so that we can easily implement them in Guile without having it as
> -	   a derivation input (they are running under a separate build user,
> -	   though).  */
> -
> -        if (useChroot && !isBuiltin(drv)) {
> +        if (useChroot) {
>              /* Initialise the loopback interface. */
>              AutoCloseFD fd(socket(PF_INET, SOCK_DGRAM, IPPROTO_IP));
>              if (fd == -1) throw SysError("cannot open IP socket");

Yes, this does fix the problem!

I wonder if I should commit this while Ludo is away?