Build with the git-lfs library when available

Otherwise use the vendored copy as before.

The library is in Debian testing but not stable. Once it reaches
stable, the vendored copy can be removed.

Did not add it to debian/control because IIRC that's used to build
git-annex on stable too, possibly. However, the Debian maintainer will
probably want to make the package depend on libghc-git-lfs-dev.

This commit was sponsored by Ilya Shlyakhter on Patreon.

CHANGELOG

@@ -3,6 +3,8 @@ git-annex (8.20200618) UNRELEASED; urgency=medium
   * Fix a deadlock that could occur after git-annex got an unlocked
     file, causing the command to hang indefinitely. Known to happen on 
     vfat filesystems, possibly others.
+  * Build with the git-lfs library when available, otherwise use the
+    vendored copy as before.
 
  -- Joey Hess <id@joeyh.name>  Thu, 18 Jun 2020 12:21:14 -0400
 

Remote/GitLFS.hs

@@ -6,6 +6,7 @@
  -}
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP #-}
 
 module Remote.GitLFS (remote, gen, configKnownUrl) where
 
@@ -39,9 +40,14 @@ import Utility.SshHost
 import Utility.Url
 import Logs.Remote
 import Logs.RemoteState
-import qualified Utility.GitLFS as LFS
 import qualified Git.Config
 
+#ifdef WITH_GIT_LFS
+import qualified Network.GitLFS as LFS
+#else
+import qualified Utility.GitLFS as LFS
+#endif
+
 import Control.Concurrent.STM
 import Data.String
 import Network.HTTP.Types

Utility/GitLFS.hs

@@ -21,6 +21,9 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE LambdaCase #-}
 
+-- This is a vendored copy of Network.GitLFS from the git-lfs package,
+-- and will be removed once that package is available in all build
+-- environments.
 module Utility.GitLFS (
 	-- * Transfer requests
 	TransferRequest(..),

git-annex.cabal

@@ -289,6 +289,10 @@ Flag NetworkBSD
   Description: Build with network-3.0 which split out network-bsd
   Default: True
 
+Flag GitLfs
+  Description: Build with git-lfs library (rather than vendored copy)
+  Default: True
+
 source-repository head
   type: git
   location: git://git-annex.branchable.com/
@@ -407,6 +411,12 @@ Executable git-annex
   else
     Build-Depends: network (< 3.0.0.0), network (>= 2.6.3.0)
 
+  if flag(GitLfs)
+    Build-Depends: git-lfs (>= 1.1.0)
+    CPP-Options: -DWITH_GIT_LFS
+  else
+    Other-Modules: Utility.GitLFS
+
   if flag(S3)
     Build-Depends: aws (>= 0.20)
     CPP-Options: -DWITH_S3
@@ -418,6 +428,7 @@ Executable git-annex
     Other-Modules:
       Remote.WebDAV
       Remote.WebDAV.DavLocation
+
   if flag(S3) || flag(WebDAV)
     Other-Modules:
       Remote.Helper.Http
@@ -1059,7 +1070,6 @@ Executable git-annex
     Utility.FileSystemEncoding
     Utility.Format
     Utility.FreeDesktop
-    Utility.GitLFS
     Utility.Glob
     Utility.Gpg
     Utility.Hash

stack-lts-12.14.yaml

@@ -12,6 +12,7 @@ flags:
     debuglocks: false
     benchmark: false
     networkbsd: false
+    gitlfs: true
 packages:
 - '.'
 extra-deps:

stack.yaml

@@ -12,6 +12,7 @@ flags:
     debuglocks: false
     benchmark: false
     networkbsd: false
+    gitlfs: true
 packages:
 - '.'
 extra-deps: