semigroup monoid change fallout; drop ghc 7 support

Fix build with ghc 8.4, which broke due to the Semigroup Monoid change.
See https://prime.haskell.org/wiki/Libraries/Proposals/SemigroupMonoid

Dropped support for building propellor with ghc 7 (as in debian
oldstable), to avoid needing to depend on the semigroups transitional
package, but also because it's just too old to be worth supporting.

If we indeed drop ghc 7 support entirely, some code to support "jessie"
can be removed; concurrent-output can be de-embedded, and the Singletons
code can be simplified.

This commit was sponsored by Jack Hill on Patreon.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/Propellor/Property/Conductor.hs b/src/Propellor/Property/Conductor.hs
index cfeb5aa7..1a67402a 100644
--- a/src/Propellor/Property/Conductor.hs
+++ b/src/Propellor/Property/Conductor.hs
@@ -81,6 +81,7 @@ import Propellor.Types.Info
 import qualified Propellor.Property.Ssh as Ssh
 
 import qualified Data.Set as S
+import qualified Data.Semigroup as Sem
 
 -- | Class of things that can be conducted.
 --
@@ -313,9 +314,9 @@ cdesc n = "conducting " ++ n
 -- A Host's Info indicates when it's a conductor for hosts, and when it's
 -- stopped being a conductor.
 newtype ConductorFor = ConductorFor [Host]
-	deriving (Typeable, Monoid)
+	deriving (Typeable, Sem.Semigroup, Monoid)
 newtype NotConductorFor = NotConductorFor [Host]
-	deriving (Typeable, Monoid)
+	deriving (Typeable, Sem.Semigroup, Monoid)
 
 instance Show ConductorFor where
 	show (ConductorFor l) = "ConductorFor " ++ show (map hostName l)
@@ -329,7 +330,7 @@ instance IsInfo NotConductorFor where
 
 -- Added to Info when a host has been orchestrated.
 newtype Orchestrated = Orchestrated Any
-	deriving (Typeable, Monoid, Show)
+	deriving (Typeable, Sem.Semigroup, Monoid, Show)
 instance IsInfo Orchestrated where
 	propagateInfo _ = PropagateInfo False