Property types changed to use a Maybe (Propellor Result). (API change)

* Property types changed to use a Maybe (Propellor Result). (API change)
* When Nothing needs to be done to ensure a property, propellor
  will avoid displaying its description at all. The doNothing property
  is an example of such a property.

This is mostly in preparation for Monoid instances for Property types, but
is's also nice that anything that uses doNothing will avoid printing out
any message at all. At least, I think it probably is. It might potentially
be confusing for something that sometimes takes an action and sometimes
resolves to doNothing and in either case has a description set to not
always show the description. If this did turn out to be confusing, the
change to doNothing could be reverted.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.

1 files changed, 7 insertions, 4 deletions

diff --git a/src/Propellor/Property/Concurrent.hs b/src/Propellor/Property/Concurrent.hs
index e69dc17d..e729d0cb 100644
--- a/src/Propellor/Property/Concurrent.hs
+++ b/src/Propellor/Property/Concurrent.hs
@@ -64,10 +64,13 @@ concurrently p1 p2 = (combineWith go go p1 p2)
 	-- Increase the number of capabilities right up to the number of
 	-- processors, so that A `concurrently` B `concurrently` C
 	-- runs all 3 properties on different processors when possible.
-	go a1 a2 = do
+	go (Just a1) (Just a2) = Just $ do
 		n <- liftIO getNumProcessors
 		withCapabilities n $
 			concurrentSatisfy a1 a2
+	go (Just a1) Nothing = Just a1
+	go Nothing (Just a2) = Just a2
+	go Nothing Nothing = Nothing
 
 -- | Ensures all the properties in the list, with a specified amount of
 -- concurrency.
@@ -101,9 +104,9 @@ concurrentList getn d (Props ps) = property d go `addChildren` ps
 			Nothing -> return r
 			Just p -> do
 				hn <- asks hostName
-				r' <- actionMessageOn hn
-					(getDesc p)
-					(getSatisfy p)
+				r' <- case getSatisfy p of
+					Nothing -> return NoChange
+					Just a -> actionMessageOn hn (getDesc p) a
 				worker q (r <> r')
 
 -- | Run an action with the number of capabiities increased as necessary to