git-safe-push-to-checkout

#!/bin/bash

# Smarter push-to-checkout hook for when receive.denyCurrentBranch is
# set to updateInstead.  It's near-identical to git's default
# behaviour when no push-to-checkout hook is provided; however it
# additionally bails if we have emacs lockfiles indicating edits in
# progress for files which would be changed by the push-to-checkout.
#
# This means that push-to-checkout works more safely and doesn't rewrite
# files which are currently being edited in emacs with unsaved changes.

commit="$1"
#echo "push-to-checkout $commit"

die () {
    echo >&2 "$*"
    exit 1
}

if ! git cat-file -t HEAD >&/dev/null; then
    die "No history yet"
fi

# The below is a more-or-less exact translation to shell of the C code for
# the default behaviour for git's push-to-checkout hook defined in the
# push_to_deploy() function in builtin/receive-pack.c
#
# However it additionally bails if we have emacs lockfiles indicating
# edits in progress for files which would be changed by the push-to-checkout.


if ! git update-index -q --ignore-submodules --refresh; then
    die "Up-to-date check failed"
fi

if ! git diff-files --quiet --ignore-submodules --; then
    die "Working directory has unstaged changes"
fi

# This is a rough translation of:
#
#    head_has_history() ? "HEAD" : EMPTY_TREE_SHA1_HEX
if git cat-file -t HEAD >&/dev/null; then
    head=HEAD
else
    head=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

if ! git diff-index --quiet --cached --ignore-submodules $head --; then
    die "Working directory has staged changes"
fi

if [[ "`pwd`" == */.git ]]; then
    # Not a bare repo; check for emacs lockfiles
    #git diff-tree HEAD $commit --
    cd ..

    while read srcmode dstmode src dst status src dst; do
        if [ -L ".#$src" ]; then
            die "emacs lockfile present for $src; can't update"
        fi
        if [ -n "$dst" -a -L ".#$dst" ]; then
            die "emacs lockfile present for $dst; can't update"
        fi
    done < <(git diff-tree HEAD $commit --)
fi

if ! git read-tree -u -m $commit; then
    die "Could not update working tree to new HEAD"
fi