add standard pre-push hook that runs basic gradle checks

hooks/pre-push

+#!/bin/sh
+
+# An hook script to verify what is about to be pushed.  Called by "git
+# push" after it has checked the remote status, but before anything has been
+# pushed.  If this script exits with a non-zero status nothing will be pushed.
+#
+# This hook is called with the following parameters:
+#
+# $1 -- Name of the remote to which the push is being done
+# $2 -- URL to which the push is being done
+#
+# If pushing without using a named remote those arguments will be equal.
+#
+# Information about the commits which are being pushed is supplied as lines to
+# the standard input in the form:
+#
+#   <local ref> <local sha1> <remote ref> <remote sha1>
+
+remote="$1"
+url="$2"
+
+z40=0000000000000000000000000000000000000000
+
+IFS=' '
+while read local_ref local_sha remote_ref remote_sha
+do
+    if [ ! "$local_sha" = $z40 ] # not deleting from remote
+    then
+        if [ "$remote_sha" = $z40 ]
+        then
+            # New branch, examine all commits
+            range="$local_sha"
+        else
+            # Update to existing branch, examine new commits
+            range="$remote_sha..$local_sha"
+        fi
+
+        if echo $url | grep 'gitlab.com[/:]fdroid/fdroidclient'; then
+            # Check for DO NOT MERGE commit
+            commit=`git rev-list -n 1 --grep 'DO NOT MERGE' "$range"`
+            if [ -n "$commit" ]
+            then
+                echo "Found DO NOT MERGE commit in $local_ref, not pushing"
+                exit 1
+            fi
+
+            # Check for WIP commit
+            commit=`git rev-list -n 1 --grep '^WIP' "$range"`
+            if [ -n "$commit" ]
+            then
+                echo "Found WIP commit in $local_ref, not pushing"
+                exit 1
+            fi
+        fi
+
+        gradle checkstyle pmd lint || exit 1
+    fi
+done
+
+exit 0