Server hook custom error messages not displayed when merge fails

Summary

Merge requests that fail to merge due to a server hook rejecting the change do not display the custom error message in the UI.

Steps to reproduce

  1. Create a repository with a single file such as README.md.
  2. Clone the repository.
  3. Edit the file and push the change to a new branch.
  4. Create a server hook on the filesystem using the listed example hook:
#!/bin/sh
echo "GL-HOOK-ERR: My custom error message.";
exit 1
  1. Ensure the file is owned by the git user and has execute permissions.
  2. Create a merge request for the branch.
  3. Attempt to merge the branch.
  4. The merge request fails to merge.

As a follow-up, change the hook to exit 0 and verify the merge can succeed which indicates the hook is being executed.

Example Project

This is reproduced by an empty repository with only a single file required to produce a non-empty merge request.

What is the current bug behavior?

The merge box says "Something went wrong during merge pre-receive hook..." but does not contain the custom error message. See screenshot.

basic-hook-no-details

What is the expected correct behavior?

The merge box should include the custom error message which provides necessary details to the user.

Relevant logs and/or screenshots

2021-11-19T16:07:06.246Z: root/test!2 - Git merge started on JID b04e14b7949db710c5c1340c
2021-11-19T16:07:06.562Z: MergeService ERROR: root/test!2 - Something went wrong during merge pre-receive hook.
2021-11-19T16:08:37.651Z: root/test!2 - Git merge started on JID 51be18dd9b46db21fdea536b
2021-11-19T16:08:37.961Z: MergeService ERROR: root/test!2 - Something went wrong during merge pre-receive hook.
2021-11-19T16:08:53.837Z: root/test!2 - Git merge started on JID c912066f1bf7dea1ab1778a2
2021-11-19T16:08:54.185Z: root/test!2 - Git merge finished on JID c912066f1bf7dea1ab1778a2 commit c6b559e3a2fb25f85cd49c882ef2ce2a3174a302
2021-11-19T16:08:54.227Z: Updating statistics for project 2
2021-11-19T16:08:54.604Z: root/test!2 - Post merge started on JID c912066f1bf7dea1ab1778a2 with state locked
2021-11-19T16:08:55.448Z: root/test!2 - Post merge finished on JID c912066f1bf7dea1ab1778a2 with state merged
2021-11-19T16:08:55.456Z: root/test!2 - Merge process finished on JID  with state merged
2021-11-19T16:21:56.217Z: ActiveRecord connection established

Output of checks

Results of GitLab environment info

This was reproduced using the GitLab docker images 14.3.3-ee.0 and persisted after upgrading to latest which at time of writing is 14.4.2-ee. I was logged in as the root user.

Expand for output related to GitLab environment info 
root@gitlab:/var/log/gitlab# gitlab-rake gitlab:env:info

System information
System:
Proxy:          no
Current User:   git
Using RVM:      no
Ruby Version:   2.7.4p191
Gem Version:    3.1.4
Bundler Version:2.1.4
Rake Version:   13.0.6
Redis Version:  6.0.16
Git Version:    2.33.0.
Sidekiq Version:6.2.2
Go Version:     unknown

GitLab information
Version:        14.4.2-ee
Revision:       84aa6daaffd
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     12.7
URL:            http://gitlab.example.com:8929
HTTP Clone URL: http://gitlab.example.com:8929/some-group/some-project.git
SSH Clone URL:  ssh://git@gitlab.example.com:2224/some-group/some-project.git
Elasticsearch:  no
Geo:            no
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers: 

GitLab Shell
Version:        13.21.1
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
GitLab Shell path:              /opt/gitlab/embedded/service/gitlab-shell
Git:            /opt/gitlab/embedded/bin/git
root@gitlab:/var/log/gitlab#

Results of GitLab application Check

Expand for output related to the GitLab application check 
root@gitlab:/var/log/gitlab# gitlab-rake gitlab:check SANITIZE=true
Checking GitLab subtasks ...                   

Checking GitLab Shell ...


GitLab Shell: ... GitLab Shell version >= 13.21.1 ? ... OK (13.21.1)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check

Internal API available: OK
Redis available via internal API: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Gitaly ...


Gitaly: ... default ... OK


Checking Gitaly ... Finished


Checking Sidekiq ...


Sidekiq: ... Running? ... yes
Number of Sidekiq processes (cluster/worker) ... 1/1


Checking Sidekiq ... Finished


Checking Incoming Email ...


Incoming Email: ... Reply by email is disabled in config/gitlab.yml


Checking Incoming Email ... Finished


Checking LDAP ...


LDAP: ... LDAP is disabled in config/gitlab.yml


Checking LDAP ... Finished


Checking GitLab App ...


Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet)
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
2/1 ... yes
1/2 ... yes
Redis version >= 5.0.0? ... yes
Ruby version >= 2.7.2 ? ... yes (2.7.4)
Git version >= 2.33.0 ? ... yes (2.33.0)
Git user has default SSH configuration? ... yes
Active users: ... 1
Is authorized keys file accessible? ... yes
GitLab configured to store new projects in hashed storage? ... yes
All projects are in hashed storage? ... yes
Elasticsearch version 7.x (6.4 - 6.x deprecated to be removed in 13.8)? ... skipped (elasticsearch is disabled)


Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished


root@gitlab:/var/log/gitlab#

Possible fixes