Submodule commit checker pre-receive server-side git hook

pre-receive

#!/bin/bash

# Service side git pre-receive hook
# Written by Gautier Pelloux-Prayer <gautier+git@damsy.net>, 2014
#
# Public domain
#
# Simply put this script in server git bare repository <your-git-folder>/hooks and
# apply 'chmod +x pre-receive'.
#
# Prevent pushing invalid submodule reference in a git repository:
# - reference to non-yet-pushed submodule commit "reference is not a tree" error
# by forcing user to push submodules first.  This is based on the following information:
# http://stackoverflow.com/questions/3418674/bash-shell-script-function-to-verify-git-tag-or-commit-exists-and-has-been-pushe
# - unwanted submodule downgrading or branch switching, mainly caused by previously
# forgot call to 'git submodule pull'. User can still do that if the commit message specify it.

ENABLE_DEBUG=0

function ECHO_DEBUG { [ $ENABLE_DEBUG = 1 ] && echo "$@" }

# get the previous commit ID, new commit ID, and ref
read oldoldrev newrev ref

# creating or deleting branch, no need to check
if [ ${oldoldrev:0:8} = "00000000" ] || [ ${newrev:0:8} = "00000000" ]; then
	exit 0
fi
commit_msg=$(git log --format=%s -n 1 $newrev)

ECHO_DEBUG "$oldoldrev $newrev $ref msg='$commit_msg'"

# Get a list of submodules
git config --file <(git show $ref:.gitmodules) --get-regexp 'submodule..*.path' |
while read key path; do
    url=$(git config --file <(git show $ref:.gitmodules) --get "${key/.path/.url}")

    # submodules URL are (mainly) absolute URLs: eg git://some.random.url.org/a-repository
    # hook can only check for local repositories stored on the same filesystem, so we assume that
    # if this is our submodule, it will be located at ../a-repository.git
    url=$(echo $url | sed -nE 's|.*/(.*)$|../\1.git|p')
    if [ ! -d "$url" ]; then
        ECHO_DEBUG "Modified submodule $url but could not find it locally! Canceling check..."
        continue
    fi
    # get absolute URL
    url=$(cd $url && pwd)

    # foreach commit being pushed, check if this one has been modified
    git diff "$ref..$newrev" -- "$path" | grep '^-Subproject commit' -A1 | cut -d' ' -f3 |
    while read sub_old_rev && read sub_new_rev; do
        ECHO_DEBUG        echo "Checking submodule update: old=$sub_old_rev -> $sub_new_rev"
        ECHO_DEBUG        echo "$commit_msg | $url"
        # for each submodule updated, check if the commit exists
        LINES=$(GIT_DIR="$url" git branch --contains "$sub_new_rev" 2>/dev/null | wc -l)
        if [ $LINES == 0 ]; then
            echo "*****************************************"
            echo "Error in ${newrev:0:8}($commit_msg):"
            echo "  Subcommit '${sub_new_rev:0:8}' not found in submodule '$path' ($url)." >&2
            echo "  Please push that submodule first!" >&2
            echo "*****************************************"
            exit 1
        else
            # and also check that the new reference is NOT parent of the old reference (submodule downgrade)
            if GIT_DIR="$url" git rev-list "$sub_old_rev" | grep -q "$sub_new_rev"; then
                expc_pattern="[Outgrade submodule]"
                if grep -Fq "$expc_pattern" <<< "$commit_msg"; then
                    echo "*****************************************"
                    echo "Warning! You are going to out-grade submodule '$path' from ${sub_old_rev:0:8} to ${sub_new_rev:0:8}, but since your commit message contains '$expc_pattern', I'll let you do that."
                    echo "*****************************************"
                else
                    echo "*****************************************"
                    echo "Error in ${newrev:0:8}($commit_msg):"
                    echo "    Error! You are trying to out-grade submodule '$path' from ${sub_old_rev:0:8} to ${sub_new_rev:0:8}, which usually means you forgot to execute 'git submodule update'. Did you?"
                    echo "    If you REALLY want to OUTGRADE submodule '$path', please add '$expc_pattern' in your commit message (id='${newrev:0:8}') using 'git commit --amend'. Current message is: '$commit_msg'".
                    echo "*****************************************"
                    exit 1
                fi
            # finally check that old reference IS reference of new reference (submodule branch switch)
            elif ! GIT_DIR="$url" git rev-list "$sub_new_rev" | grep -q "$sub_old_rev"; then
                expc_pattern="[Switch submodule branch]"
                if grep -Fq "$expc_pattern" <<< "$commit_msg"; then
                    echo "*****************************************"
                    echo "Warning! You are going to switch submodule branch '$path' from ${sub_old_rev:0:8} to ${sub_new_rev:0:8}, but since your commit message contains '$expc_pattern', I'll let you do that."
                    echo "*****************************************"
                else
                    echo "*****************************************"
                    echo "Error in ${newrev:0:8}($commit_msg):"
                    echo "    Error! You are trying to switch submodule branch '$path' from ${sub_old_rev:0:8} to ${sub_new_rev:0:8}, which usually means you forgot to execute 'git submodule update'. Did you?"
                    echo "    If you REALLY want to SWITCH BRANCH submodule '$path', please add '$expc_pattern' in your commit message (id='${newrev:0:8}') using 'git commit --amend'. Current message is: '$commit_msg'".
                    echo "*****************************************"
                    exit 1
                fi
            fi
        fi
    done || exit 1
done || exit 1

exit 0