Thanks @regnat and @edolstra for catching this and comming up with the
solution.
They way I had generalized those is wrong, because local settings for
non-local stores is confusing default. And due to the nature of C++
inheritance, fixing the defaults is more annoying than it should be.
Additionally, I thought we might just drop the check in the substitution
logic since `Store::addToStore` is now streaming, but @regnat rightfully
pointed out that as it downloads dependencies first, that would still be
too late, and also waste effort on possibly unneeded/unwanted
dependencies.
The simple and correct thing to do is just make a store method for the
boolean logic, keeping all the setting and key stuff the way it was
before. That new method is both used by `LocalStore::addToStore` and the
substitution goal check. Perhaps we might eventually make it fancier,
e.g. sending the ValidPathInfo to remote stores for them to validate,
but this is good enough for now.
By default, once you enter x86_64 Rosetta 2, macOS will try to run
everything in x86_64. So an x86_64 Nix will still try to use x86_64
even when system = aarch64-darwin. To avoid this we can set
kern.curproc_arch_affinity sysctl. With kern.curproc_arch_affinity=0,
we ignore this preference.
This is based on how
https://opensource.apple.com/source/system_cmds/system_cmds-880.40.5/arch.tproj/arch.c.auto.html
works. Completely undocumented, but seems to work!
Note, you can verify this works with this impure Nix expression:
```
{
a = derivation {
name = "a";
system = "aarch64-darwin";
builder = "/bin/sh";
args = [ "-e" (builtins.toFile "builder" ''
[ "$(/usr/bin/arch)" = arm64 ]
[ "$(/usr/bin/arch -arch x86_64 /bin/sh -c /usr/bin/arch)" = i386 ]
[ "$(/usr/bin/arch -arch arm64 /bin/sh -c /usr/bin/arch)" = arm64 ]
/usr/bin/touch $out
'') ];
};
b = derivation {
name = "b";
system = "x86_64-darwin";
builder = "/bin/sh";
args = [ "-e" (builtins.toFile "builder" ''
[ "$(/usr/bin/arch)" = i386 ]
[ "$(/usr/bin/arch -arch x86_64 /bin/sh -c /usr/bin/arch)" = i386 ]
[ "$(/usr/bin/arch -arch arm64 /bin/sh -c /usr/bin/arch)" = arm64 ]
/usr/bin/touch $out
'') ];
};
}
```
This resolves#3810 by changing the behavior of `max-jobs = 0`, so
that specifying the option also avoids local building of derivations
with the attribute `preferLocalBuild = true`.
It appears as through the fetch attribute, which
is simply a variant with 3 elements, implicitly
converts boolean arguments to integers. One must
use Explicit<bool> to correctly populate it with
a boolean. This was missing from the implementation,
and resulted in clearly boolean JSON fields being
treated as numbers.
libc++10 seems to be stricter on what it allows in variant conversion.
I'm not sure what the rules are here, but this is the minimal change
needed to get through the compilation errors.
