fsmonitor: handle version 2 of the hooks that will use opaque token

Some file monitors like watchman will use something other than a timestamp
to keep better track of what changes happen in between calls to query
the fsmonitor. The clockid in watchman is a string. Now that the index
is storing an opaque token for the last update the code needs to be
updated to pass that opaque token to a verion 2 of the fsmonitor hook.

Because there are repos that already have version 1 of the hook and we
want them to continue to work when git is updated, we need to handle
both version 1 and version 2 of the hook. In order to do that a
config value is being added core.fsmonitorHookVersion to force what
version of the hook should be used.  When this is not set it will default
to -1 and then the code will attempt to call version 2 of the hook first.
If that fails it will fallback to trying version 1.

Signed-off-by: Kevin Willford <Kevin.Willford@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 1 insertions, 3 deletions

diff --git a/t/t7519/fsmonitor-all b/t/t7519/fsmonitor-all
index 691bc94dc2..94ab66bd3d 100755
--- a/t/t7519/fsmonitor-all
+++ b/t/t7519/fsmonitor-all
@@ -17,7 +17,6 @@ fi
 
 if test "$1" != 1
 then
-	echo "Unsupported core.fsmonitor hook version." >&2
 	exit 1
 fi
 
diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
index d8e7a1e5ba..264b9daf83 100755
--- a/t/t7519/fsmonitor-watchman
+++ b/t/t7519/fsmonitor-watchman
@@ -26,8 +26,7 @@ if ($version == 1) {
 	# subtract one second to make sure watchman will return all changes
 	$time = int ($time / 1000000000) - 1;
 } else {
-	die "Unsupported query-fsmonitor hook version '$version'.\n" .
-	    "Falling back to scanning...\n";
+	exit 1;
 }
 
 my $git_work_tree;