Fix wrong sorting of remotes when using -J

It was sorting by uuid, rather than cost!

Avoid future bugs of this kind by changing the Ord to primarily compare
by cost, with uuid only used when the cost is the same.

This commit was supported by the NSF-funded DataLad project.

Annex/Transfer.hs

@@ -279,4 +279,4 @@ pickRemote l a = go l =<< Annex.getState Annex.concurrency
 lessActiveFirst :: M.Map Remote Integer -> Remote -> Remote -> Ordering
 lessActiveFirst active a b
 	| Remote.cost a == Remote.cost b = comparing (`M.lookup` active) a b
-	| otherwise = compare a b
+	| otherwise = comparing Remote.cost a b

CHANGELOG

@@ -8,6 +8,8 @@ git-annex (6.20180720) UNRELEASED; urgency=medium
   * Added --accessedwithin matching option.
   * Added annex.commitmessage config that can specify a commit message
     for the git-annex branch instead of the usual "update".
+  * Fix wrong sorting of remotes when using -J, it was sorting by uuid,
+    rather than cost.
 
  -- Joey Hess <id@joeyh.name>  Tue, 31 Jul 2018 12:14:11 -0400
 

Types/Remote.hs

@@ -146,8 +146,13 @@ instance Show (RemoteA a) where
 instance Eq (RemoteA a) where
 	x == y = uuid x == uuid y
 
+-- Order by cost since that is the important order of remotes
+-- when deciding which to use. But since remotes often have the same cost
+-- and Ord must be total, do a secondary ordering by uuid.
 instance Ord (RemoteA a) where
-	compare = comparing uuid
+	compare a b
+		| cost a == cost b = comparing uuid a b
+		| otherwise = comparing cost a b
 
 instance ToUUID (RemoteA a) where
 	toUUID = uuid

doc/tips/local_caching_of_annexed_files/comment_9_7db7787a306c70ba3c1687c1d103608d._comment

@@ -0,0 +1,9 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 9"""
+ date="2018-08-03T16:30:35Z"
+ content="""
+The -J2 web bug was not related to caching remotes at all
+but was an accidental sort by remote uuid rather than cost.
+I've fixed it.
+"""]]