annex.sshcaching warning improvement and allow overridding build time default

* When git-annex is built with a ssh that does not support ssh connection
  caching, default annex.sshcaching to false, but let the user override it.
* Improve warning messages further when ssh connection caching cannot
  be used, to clearly state why.

Annex/Ssh.hs

@@ -98,46 +98,31 @@ consumeStdinParams NoConsumeStdin = [Param "-n"]
 {- Returns a filename to use for a ssh connection caching socket, and
  - parameters to enable ssh connection caching. -}
 sshCachingInfo :: (SshHost, Maybe Integer) -> Annex (Maybe FilePath, [CommandParam])
-sshCachingInfo (host, port) = go =<< sshCacheDir
+sshCachingInfo (host, port) = go =<< sshCacheDir'
   where
-	go (Just dir) =
+	go (Right dir) =
 		liftIO (bestSocketPath $ dir </> hostport2socket host port) >>= return . \case
 			Nothing -> (Nothing, [])
 			Just socketfile -> (Just socketfile, sshConnectionCachingParams socketfile)
 	-- No connection caching with concurrency is not a good
 	-- combination, so warn the user.
-	go Nothing = do
+	go (Left whynocaching) = do
 		Annex.getState Annex.concurrency >>= \case
                 	NonConcurrent -> return ()
-			Concurrent {} -> warnnocaching
-			ConcurrentPerCpu -> warnnocaching
+			Concurrent {} -> warnnocaching whynocaching
+			ConcurrentPerCpu -> warnnocaching whynocaching
 		return (Nothing, [])
 	
-	warnnocaching = do
+	warnnocaching whynocaching = do
 		warning nocachingwarning
-		ifM (fromMaybe True . annexSshCaching <$> Annex.getGitConfig)
-			( whenM crippledFileSystem $
-				warning crippledfswarning
-			, warning enablecachingwarning
-			)
+		warning whynocaching
 	
 	nocachingwarning = unwords
-		[ "You have enabled concurrency, but ssh connection caching"
-		, "is not enabled. This may result in multiple ssh processes"
-		, "prompting for passwords at the same time."
+		[ "You have enabled concurrency, but git-annex is not able"
+		, "to use ssh connection caching. This may result in"
+		, "multiple ssh processes prompting for passwords at the"
+		, "same time."
 		]
-	
-	crippledfswarning = unwords
-		[ "This repository is on a crippled filesystem, so unix named"
-		, "pipes probably don't work, and ssh connection caching"
-		, "relies on those. One workaround is to set"
-		, sshSocketDirEnv
-		, "to point to a directory on a non-crippled filesystem."
-		, "(Or, disable concurrency.)"
-		]
-	
-	enablecachingwarning = 
-		"Enable annex.sshcaching (or disable concurrency) to avoid this problem."
 
 {- Given an absolute path to use for a socket file,
  - returns whichever is shorter of that or the relative path to the same
@@ -172,22 +157,37 @@ sshSocketDirEnv = "GIT_ANNEX_SSH_SOCKET_DIR"
 {- ssh connection caching creates sockets, so will not work on a
  - crippled filesystem. -}
 sshCacheDir :: Annex (Maybe FilePath)
-sshCacheDir
-	| BuildInfo.sshconnectioncaching = 
-		ifM (fromMaybe True . annexSshCaching <$> Annex.getGitConfig)
-			( ifM crippledFileSystem
-				( maybe (return Nothing) usetmpdir =<< gettmpdir
-				, Just <$> fromRepo gitAnnexSshDir 
-				)
-			, return Nothing
+sshCacheDir = eitherToMaybe <$> sshCacheDir'
+
+sshCacheDir' :: Annex (Either String FilePath)
+sshCacheDir' = 
+	ifM (fromMaybe BuildInfo.sshconnectioncaching . annexSshCaching <$> Annex.getGitConfig)
+		( ifM crippledFileSystem
+			( gettmpdir >>= \case
+				Nothing ->
+					return (Left crippledfswarning)
+				Just tmpdir -> 
+					liftIO $ catchMsgIO $
+						usetmpdir tmpdir
+			, Right <$> fromRepo gitAnnexSshDir 
 			)
-	| otherwise = return Nothing
+		, return (Left "annex.sshcaching is not set to true")
+		)
   where
 	gettmpdir = liftIO $ getEnv sshSocketDirEnv
-	usetmpdir tmpdir = liftIO $ catchMaybeIO $ do
+
+	usetmpdir tmpdir = do
 		let socktmp = tmpdir </> "ssh"
 		createDirectoryIfMissing True socktmp
 		return socktmp
+	
+	crippledfswarning = unwords
+		[ "This repository is on a crippled filesystem, so unix named"
+		, "pipes probably don't work, and ssh connection caching"
+		, "relies on those. One workaround is to set"
+		, sshSocketDirEnv
+		, "to point to a directory on a non-crippled filesystem."
+		]
 
 portParams :: Maybe Integer -> [CommandParam]
 portParams Nothing = []

CHANGELOG

@@ -1,3 +1,12 @@
+git-annex (7.20200205) UNRELEASED; urgency=medium
+
+  * When git-annex is built with a ssh that does not support ssh connection
+    caching, default annex.sshcaching to false, but let the user override it.
+  * Improve warning messages further when ssh connection caching cannot
+    be used, to clearly state why.
+
+ -- Joey Hess <id@joeyh.name>  Fri, 14 Feb 2020 14:12:25 -0400
+
 git-annex (7.20200204) upstream; urgency=medium
 
   * Fix build with persistent-template 2.8.0.

doc/bugs/warning_about_ssh_caching_keeps_showing.mdwn

@@ -55,3 +55,5 @@ local repository version: 7
 I've been using git-annex for 1.5 years to manage bioinformatics analyses.  It's a very versatile and well-designed tool.  I've been able to adapt it to many use cases;
 the ability to easily write your own external backends has been especially helpful for that.  The amount of work and thought that has gone into designing/building git-annex is
 enormous, and very much appreciated.
+
+> [[done]]; see comment --[[Joey]]

doc/bugs/warning_about_ssh_caching_keeps_showing/comment_1_711a8e784ba8fde0164469fa08176687._comment

@@ -0,0 +1,25 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2020-02-14T17:48:41Z"
+ content="""
+It seems you must have annex.jobs set to something, since concurrency
+is enabled without any -J option, so the easy fix is just to unset that.
+
+It kind of looks like your build of git-annex may have been made without
+ssh connection caching support, which would happen if its configure program
+detected at build time that ssh doesn't support it.
+
+That would be unusual if so, all the builds of git-annex that I'm aware of
+are made with ssh that does support it.
+
+There are a couple of even less likely scenarios, like
+`GIT_ANNEX_SSH_SOCKET_DIR` being set to a directory you can't write to.
+
+I've changed the code to always say explicitly why ssh caching can't be
+enabled. I also let annex.sshcaching override the build-time detection.
+
+I guess that's enough to close this, unless it turns out its
+reasons for not enabling it are not one of those I mentioned above, but
+something entirely bogus.
+"""]]