Make install_hooks check if git hook is available

When git hook isn't available, we can still have
install_hooks.sh copy the commands to .git/hooks. However, this means
that the hooks will not remain up-to-date as this repository is updated,
so the user is warned.

Bug: b/187094215
Change-Id: I7401b78d7e6afa12fec691efed7c21b62d987422

install_hooks.sh

diff --git a/install_hooks.sh b/install_hooks.sh
index 822a324..681e1a1 100755
--- a/install_hooks.sh
+++ b/install_hooks.sh
@@ -6,20 +6,32 @@
 # Space separated list of hooks to install
 declare -a HOOKS=("pre-commit" "commit-msg")
 
+hookConfigExists="$(git hook list pre-commit 2>/dev/null >> /dev/null ; echo $?)"
+
 for hook in ${HOOKS[@]}; do
     if [ ! -f "${dir}/${hook}" ]; then
         continue
     fi
-
     # Soft remove the old script in .git/hooks so that git doesn't try to run
     # multiple hooks.
     if [ -f "${githookdir}/${hook}" ]; then
         mv "${githookdir}/${hook}" "${githookdir}/${hook}.old"
     fi
+    if [ "$hookConfigExists" -eq "0" ]; then
+        git config --unset-all hook.${hook}.command
+        git config --add hook.${hook}.command "${dir}/${hook}"
+        # There should be a single hook per line and it should point to the
+        # git-hooks repository.
+        git hook list "${hook}"
+    else
+        cp ${dir}/${hook} ${githookdir}/${hook}
+    fi
+done
 
-    git config --unset-all hook.${hook}.command
-    git config --add hook.${hook}.command "${dir}/${hook}"
-    # Sanity check: there should be a single hook per line and it should point to the
-    # git-hooks repository.
-    git hook list "${hook}"
+if [ "$hookConfigExists" -eq "0" ]; then
+    echo "If a single command is listed per hook, then this script was succesful."
+    echo "Checks will be run at pre-submit."
+else
+    echo "The 'git hook' command is not available on this device."
+    echo "The hooks will be copied to ${githookdir}, but will not automatically remain up-to-date with the git-hooks repository"
 done