installer media can be used on top of existing host configs. In such
scenarions, root fs types will already be defined.
Before this change, this will inevitably lead to the following error:
```console
error: The option `fileSystems./.fsType' has conflicting definition values:
- In `/nix/store/2nl5cl4mf6vnldpbxhrbzfh0n8rsv9fm-source/DevOS/os/hardware/common.nix': "ext4"
- In `/nix/store/jbch90yqx6gg1h3fq30jjj2b6h6jfjgs-source/nixos/modules/installer/cd-dvd/iso-image.nix': "tmpfs"
```
With this patch, the installers will override those values according to
their own local requirement.
Use `mkOverride 60` so that conscientious overriding specially targeted
at the installer, e.g. with `mkForce` is still straight forward.
(cherry picked from commit c219fdffad3fa76c43824bee34d5fb424ff95b87)
Without this, failure of nixBuild() and nixFlakeBuild() was ignored
(since bash doesn't inherit 'set -e' in subshells by default), so the
script would proceed with a bogus ./result link, e.g.
++ readlink -f /tmp/nixos-rebuild.NfHKxx/result
+ pathToConfig='/nix/store/m7dvk6an18cpr95qn5wnig2600qhv6w7-nix-2.4pre20210727_706777a/bin/nix
/tmp/nixos-rebuild.NfHKxx/result'
+ '[' test = switch -o test = boot ']'
+ copyToTarget '/nix/store/m7dvk6an18cpr95qn5wnig2600qhv6w7-nix-2.4pre20210727_706777a/bin/nix
/tmp/nixos-rebuild.NfHKxx/result'
+ '[' '' = '' ']'
+ '[' test = switch -o test = boot -o test = test -o test = dry-activate ']'
+ targetHostCmd /nix/store/m7dvk6an18cpr95qn5wnig2600qhv6w7-nix-2.4pre20210727_706777a/bin/nix /tmp/nixos-rebuild.NfHKxx/result/bin/switch-to-configuration test
+ '[' -z '' ']'
+ sudo -- /nix/store/m7dvk6an18cpr95qn5wnig2600qhv6w7-nix-2.4pre20210727_706777a/bin/nix /tmp/nixos-rebuild.NfHKxx/result/bin/switch-to-configuration test
error: '/tmp/nixos-rebuild.NfHKxx/result/bin/switch-to-configuration' is not a recognised command
Try '/nix/store/m7dvk6an18cpr95qn5wnig2600qhv6w7-nix-2.4pre20210727_706777a/bin/nix --help' for more information.
+ echo 'warning: error(s) occurred while switching to the new configuration'
warning: error(s) occurred while switching to the new configuration
(cherry picked from commit 0ad27c8653daaf59cf0fb2e0b30561a8d86303fa)
The conclusion is that Phabricator does not, in fact, generate stable
patch links. In any case, these have landed, so we can just use the
patches from Mercurial's hgweb instance instead, which should be more
stable.
(cherry picked from commit 67444f8a393846b1431cfeb936e83a9f24725e2d)