pre-receive: add prevent-foxtrot script

pre-receive.d/prevent-foxtrot-merge.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+# Copyright (c) 2016 G. Sylvie Davies. http://bit-booster.com/
+# Copyright (c) 2016 torek. http://stackoverflow.com/users/1256452/torek
+# Copyright (c) 2021 Alfred Melch. https://melch.pro
+# License: MIT license. https://opensource.org/licenses/MIT
+
+# From: https://blog.developer.atlassian.com/stop-foxtrots-now/
+
+NULL_REV="0000000000000000000000000000000000000000"
+
+# refname (e.g. refs/head/master) will be updated from oldrev (commit hash) to newrev (commit hash)
+while read oldrev newrev refname
+do
+  if [ $oldrev = $NULL_REV ]; then
+    # pushing a new branch
+    exit 0
+  fi
+  if [ $newrev = $NULL_REV ]; then
+    # deleting a branch 
+    exit 0
+  fi
+  if [ "$refname" = "refs/heads/master" ] || [ "$refname" = "refs/heads/main" ]; then
+    # Find the first parent of the commit where oldrev is a parent
+    # git log: list commits from newrev to oldrev
+    #   %H: commit hash
+    #   %P: parent hashes (list of parents)
+    # grep: filter for oldrev
+    #   Should appear once as a parent
+    # awk: print the second word 
+    #   The second word is the first parent. Third word would be second parent, ...
+    MATCH=`git log --first-parent --pretty='%H %P' $oldrev..$newrev |
+      grep $oldrev |
+      awk '{ print $2 }'`
+          # First parent should be the oldrev
+          if [ "$oldrev" = "$MATCH" ]; then
+            exit 0
+          else
+            echo >&2 "*** Push rejected! Foxtrot merge blocked! ***"
+            echo "See: https://blog.developer.atlassian.com/stop-foxtrots-now/"
+            exit 1
+          fi
+  fi
+done

use-hook-dir.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+# From: https://gist.github.com/mjackson/7e602a7aa357cfe37dadcc016710931b
+
+# Make a symlink per hook to this script you use e.g. .git/hooks/pre-receive.
+# It looks for scripts in the .git/hooks/pre-receive.d directory and executes them in order,
+# passing along stdin. If any script exits with a non-zero status, this script exits.
+
+script_dir=$(dirname $0)
+hook_name=$(basename $0)
+
+hook_dir="$script_dir/$hook_name.d"
+
+if [[ -d $hook_dir ]]; then
+  stdin=$(cat /dev/stdin)
+
+  for hook in $hook_dir/*; do
+    echo "$stdin" | $hook "$@"
+
+    exit_code=$?
+
+    if [ $exit_code != 0 ]; then
+      exit $exit_code
+    fi
+  done
+fi
+
+exit 0