anchor.diff:          valueBuildBuild = pkgsBuildBuild.${name} or {};
           valueBuildHost = pkgsBuildHost.${name} or {};
           valueBuildTarget = pkgsBuildTarget.${name} or {};
  -        valueHostHost = throw "`valueHostHost` unimplemented: pass manually rather than relying on splice.";
  +        valueHostHost = pkgsHostHost.${name} or {};
           valueHostTarget = pkgsHostTarget.${name} or {};
           valueTargetTarget = pkgsTargetTarget.${name} or {};
           augmentedValue = defaultValue
  
positive.code:           pkgsBuildBuild = valueBuildBuild;
            pkgsBuildHost = valueBuildHost;
            pkgsBuildTarget = valueBuildTarget;
            pkgsHostHost = {};
            pkgsHostTarget = valueHostTarget;
            pkgsTargetTarget = valueTargetTarget;
          # Don't be fancy about non-derivations. But we could have used used
  
negative.code:             __spliced =
                   (lib.optionalAttrs (pkgsBuildBuild ? ${name}) { buildBuild = valueBuildBuild; })
                // (lib.optionalAttrs (pkgsBuildTarget ? ${name}) { buildTarget = valueBuildTarget; })
                // (lib.optionalAttrs (pkgsHostHost ? ${name}) { hostHost = valueHostHost; })
                // (lib.optionalAttrs (pkgsTargetTarget ? ${name}) { targetTarget = valueTargetTarget;
            });
          };
  