testremote: Fix crash when testing a freshly made external special remote.

Ignore exceptions when getting the cost and availability for the remote,
and return sane defaults. These defaults are not cached, so if a special
remote program has a transient problem, it will re-query it later.

CHANGELOG

@@ -5,6 +5,7 @@ git-annex (6.20160614) UNRELEASED; urgency=medium
     Thanks, Farhan Kathawala.
   * get: Add --batch and --json options.
   * New url for git-remote-gcrypt, now maintained by spwhitton.
+  * testremote: Fix crash when testing a freshly made external special remote.
 
  -- Joey Hess <id@joeyh.name>  Mon, 13 Jun 2016 21:52:24 -0400
 

Remote/External.hs

@@ -461,16 +461,17 @@ checkPrepared lck external =
  - external special remote every time time just to ask it what its
  - cost is. -}
 getCost :: External -> Git.Repo -> RemoteGitConfig -> Annex Cost
-getCost external r gc = go =<< remoteCost' gc
+getCost external r gc = catchNonAsync (go =<< remoteCost' gc) (const defcst)
   where
 	go (Just c) = return c
 	go Nothing = do
 		c <- handleRequest external GETCOST Nothing $ \req -> case req of
 			COST c -> Just $ return c
-			UNSUPPORTED_REQUEST -> Just $ return expensiveRemoteCost
+			UNSUPPORTED_REQUEST -> Just defcst
 			_ -> Nothing
 		setRemoteCost r c
 		return c
+	defcst = return expensiveRemoteCost
 
 {- Caches the availability in the git config to avoid needing to start up an
  - external special remote every time time just to ask it what its
@@ -480,15 +481,17 @@ getCost external r gc = go =<< remoteCost' gc
  - globally available is the default.
  -}
 getAvailability :: External -> Git.Repo -> RemoteGitConfig -> Annex Availability
-getAvailability external r gc = maybe query return (remoteAnnexAvailability gc)
+getAvailability external r gc = 
+	maybe (catchNonAsync query (const defavail)) return (remoteAnnexAvailability gc)
   where
 	query = do
 		avail <- handleRequest external GETAVAILABILITY Nothing $ \req -> case req of
 			AVAILABILITY avail -> Just $ return avail
-			UNSUPPORTED_REQUEST -> Just $ return GloballyAvailable
+			UNSUPPORTED_REQUEST -> Just defavail
 			_ -> Nothing
 		setRemoteAvailability r avail
 		return avail
+	defavail = return GloballyAvailable
 
 claimurl :: External -> URLString -> Annex Bool
 claimurl external url =

doc/bugs/race_condition_with___39____39__git-annex__58___Cannot_run_git-annex-remote-__33__dne__33___--_Make_sure_it__39__s_in_your_PATH_and_is_executable.__34__.mdwn

@@ -1,3 +1,5 @@
+[[!metatitle="testremote of external special remote fails with 'Cannot run git-annex-remote-!dne!'"]]
+
 ### Please describe the problem.
 
 When git-annex has not recently used a remote, there appears to be a race condition where sometimes it will fail with "git-annex: Cannot run git-annex-remote-!dne! -- Make sure it's in your PATH and is executable."
@@ -17,3 +19,4 @@ Output: https://gitlab.com/DanielDent/git-annex-remote-rclone/builds/2166902
 
 The 'git-annex copy test --to GA-rclone-CI' line prior to the 'testremote' invocation seems to warm caches and avoids having the bug trigger.
 
+> [[fixed|done]] --[[Joey]]

doc/bugs/race_condition_with___39____39__git-annex__58___Cannot_run_git-annex-remote-__33__dne__33___--_Make_sure_it__39__s_in_your_PATH_and_is_executable.__34__/comment_1_2960102ff86d8b0304d6fd8b83e34ba1._comment

@@ -0,0 +1,20 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2016-07-05T19:58:41Z"
+ content="""
+AFAICS this can only affect `git annex testremote` and not other commands; 
+to test behavior when the remote is not accessible, it uses
+mkUnavailable which substitutes "!dne!" for various values. 
+
+In the case of an external special remote, this causes it to run
+git-annex-remote-!dne! which is intentially not in the PATH. So, 
+testremote is testing the behavior when the external special remote
+program is missing.
+
+The bug is that in the remote warmup process it tries to run
+git-annex-remote-!dne! in order to query it for GETCOST, and this fails.
+
+It's not a race condition; it just fails the first time, and works
+the second time (since it has gotten the cost cached then).
+"""]]