Test push conflicts on git push via Pre-Receive Hook - bash

Question

I'm making a Pre-Receive Hook on BitBucket that is supposed to confirm that all pushes made in a branch are up-to-date with parent Branches.
I mean, in a temporal evolution, we have several branches creations:
Branch creation during time
With the above example os 3 branches, Dev, Feature1, and my Local, i want to, before making push of Local to remote/origins/Feature1, make git merge from the latest Feature1 with the recent on-push Local Code. In this way, i can confirm that, whoever is making the push, is using the latest version of feature1, and there will be no conflict.
If it were any conflict, i would return 1, to avoid making the push! and obligate the Developer to pull from Feature before push is code.
This is my script on Pre-Receive Hook.
while read from_ref to_ref ref_name; do
echo "Ref update:"
echo " Old value: $from_ref"
echo " New value: $to_ref"
echo " Ref name: $ref_name"
echo " Diff:"
git clone --progress -v $GIT_URL $CLONE_DIR1
cd $CLONE_DIR1
git checkout -b test remotes/origin/Feature1
git merge --no-commit -m "Merging feature with local on-push code" $ref_name
(....)
done
I've tried with ref_name, to_ref, and having no success.
Anyone can help me?
How can I access the recent pushed code, and merge by parent branch with this code?

Answer 1

This seems like a very odd thing to do, and it is probably doomed to failure. It will certainly be complicated and you will want to change your test behavior based on which ref(s) are being updated and whether these update add merge commit(s).
That said, there are some special rules for pre-receive and update hooks, and if you obey them you will get somewhat further:
Do not chdir or cd away from the current directory. Or, if you do, make sure you chdir back, but usually it's not too difficult to make sure that operations that must run in another directory, run as a separate process: either a sub-shell, or another script.
Remove $GIT_DIR from the environment before attempting git commands that need to use a different repository. The reason is that the hook is run in the top level directory with $GIT_DIR set to either .git (non-bare repo) or . (bare repository).
Putting those two together, you might move all your verifier code into a separate script and do something like this:
exitstatus=0
while read from_ref to_ref ref_name; do
... maybe some setup code here to see if $ref_name
is being created or destroyed ...'
case "$ref_name" in
... add cases as needed to choose action based on ref ...
if (unset GIT_DIR; /path/to/check_script arg1 arg2 ...); then
echo "push being rejected because ..."
exitstatus=1
fi
...
esac
...
done
exit $exitstatus
There is still one very big problem here. You want check_script to be able to access any proposed new commits that would become reachable from $ref_name if the hook script exits 0 so that the proposed update to it is allowed. That update has not yet occurred: $ref_name still points to the old SHA-1 $from_ref. Meanwhile, the new SHA-1 in $to_ref might not have any name pointing to it (though it does still exist in the underlying repository).
Among other things, if $to_ref points to new commits (the usual case), any clone you make at this point, via normal git operations, will not contain those commits, so you will not be able to use them.
There are two obvious ways to handle this:
Make a new (temporary) reference that points to $to_ref. You can then see the proposed commits in the clone.
Don't use a clone. Copy the repository some other way, or use the original repository itself directly, e.g., as an "alternate", or by creating a temporary work tree directory and pointing $GIT_WORK_TREE there, or using some of the new git worktree features that have appeared in git 2.6+. (If you choose the manual temporary work-tree method, be sure to think about the normal shared $GIT_INDEX_FILE as well.)
Remember also to check for forced pushes that remove commits from a branch, or even remove-some-and-add-others all in one push.

Answer 2

UPDATE:
This question is resolved for me.
The final code is this:
#!/bin/bash
DIR=xpto/external-hooks/code_review
CLONE_DIR=$DIR/test_conflict_push-$(date +%s)
GIT_URL=myGitUrl
exitStatus=0
read oldrev newrev refname
feature_branch=${refname##refs/heads/}
echo "Feature branch-> $feature_branch"
#Clone feature branch from remote repo to be update via merged.
git clone --progress -v $GIT_URL $CLONE_DIR
currentDir=$PWD
cd $CLONE_DIR
#create branch named 'latest' to put new and modify files
git checkout -b latest remotes/origin/$feature_branch
#go back to PWD otherwise cant make git diff
cd $currentDir
# Get the file names, without directory, of the files that have been modified
# between the new revision and the old revision
echo "Getting files"
files=`git diff --name-only ${oldrev} ${newrev}`
echo "Files -> $files"
# Get a list of all objects in the new revision
echo "Getting objects"
objects=`git ls-tree --full-name -r ${newrev}`
echo "objects -> $objects"
# Iterate over each of these files
for file in ${files}; do
# Search for the file name in the list of all objects
object=`echo -e "${objects}" | egrep "(\s)${file}\$" | awk '{ print $3 }'`
# If it's not present, then continue to the the next itteration
if [ -z ${object} ];
then
continue;
fi
# Otherwise, create all the necessary sub directories in the new temp directory
mkdir -p "${CLONE_DIR}/`dirname ${file}`" &>/dev/null
# and output the object content into it's original file name
git cat-file blob ${object} > ${CLONE_DIR}/${file}
done;
echo "Ready for start merging."
cd $CLONE_DIR
#add new files to branch
echo $(git add .)
#commit added and modify files to branch
echo $(git commit -a -m "Merge latest to original feature")
#get generated commit id
echo $(git log -1)
#create branch named 'merged' to merge above commited files
echo $(git checkout -b merged remotes/origin/$feature_branch)
#merge only occurs for madded and modify files!
echo "Merging committed files to 'merged' branch with from 'latest' branch."
mergeResult=$(git merge --no-commit latest)
echo "Merge Result -> $mergeResult"
##to lower case
if [[ "${mergeResult,,}" == *"conflict"* ]]
then
echo "Merge contains conflicts."
echo "Update your $feature_branch branch!"
exitStatus=1
else
echo "Merge don't contains conflict."
echo "Push to $feature_branch can proceed."
exitStatus=0
fi
#remove temporary branches
echo $(git checkout master)
echo $(git branch -D latest)
echo $(git branch -D merged)
#delete temporary clone dir
rm -rf $CLONE_DIR
exit $exitStatus
Many Thanks.