[PATCH v2] devtools: check for supported git version

[Ali Alnubani <alialnu@nvidia.com>]

The script devtools/parse-flow-support.sh uses the git-grep
option (-o, --only-matching), which is only supported from
git version 2.19 and onwards.[1]

The script now exits early providing a clear message to the user
about the required git version instead of showing the following
error messages multiple times:
  error: unknown switch `o'
  usage: git grep [<options>] [-e] <pattern> [<rev>...] [[--] <path>...]
  [..]

[1] https://github.com/git/git/blob/v2.19.0/Documentation/RelNotes/2.19.0.txt

Signed-off-by: Ali Alnubani <alialnu@nvidia.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
---
Changes in v2:
- Refer to filename by $0 (Suggested by David Marchand).

 devtools/parse-flow-support.sh | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/devtools/parse-flow-support.sh b/devtools/parse-flow-support.sh
index 63c0b20e23..9811c7881c 100755
--- a/devtools/parse-flow-support.sh
+++ b/devtools/parse-flow-support.sh
@@ -13,6 +13,12 @@ if [ -z "$dir" ]; then
 	exit 1
 fi
 
+# test git-grep for -o (--only-matching) option
+if ! git grep -qo git -- $0 >/dev/null 2>&1; then
+	echo "git version >= 2.19 is required" >&2
+	exit 1
+fi
+
 # sorting order
 export LC_COLLATE=C
 
-- 
2.25.1