squash commits checkbox on merge page does nothing

Summary

Changing the status of the Squash commits checkbox while performing a merge is ignored.

Steps to reproduce

Scenario 1:

  1. Create a MR with several commits. Check both remove source branch and squash commits.
  2. When doing the MR, uncheck squash commits and proceed with the merge.

Scenario 2:

  1. Create a MR with several commits. Check remove source branch, leave squash commits unchecked.
  2. When doing the MR, check squash commits and proceed with the merge.

What is the current bug behavior?

The merge is performed with the status of the checkbox saved while creating the MR.

What is the expected correct behavior?

The merge should be performed with the status of the checkbox on the merge page, where the merge button is clicked.

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:         Ubuntu 16.04
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.16.6
Rake Version:   12.3.1
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.3
Go Version:     unknown

GitLab information
Version:        11.6.5
Revision:       237bddc
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://gitlab.tesagon.com
HTTP Clone URL: https://gitlab.tesagon.com/some-group/some-project.git
SSH Clone URL:  git@gitlab.tesagon.com:some-group/some-project.git
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers:


GitLab Shell
Version:        8.4.3
Repository storage paths:
  • default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check 
Checking GitLab subtasks ...

Checking GitLab Shell ...


GitLab Shell: ... GitLab Shell version >= 8.4.3 ? ... OK (8.4.3)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK


Access to /var/opt/gitlab/.ssh/authorized_keys: 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 ... 1


Checking Sidekiq ... Finished


Checking Incoming Email ...


Incoming Email: ... Checking Reply by email ...


IMAP server credentials are correct? ... yes
Init.d configured correctly? ... skipped
MailRoom running? ... skipped


Checking Reply by email ... Finished


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? ... yes
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: ...
4/1 ... yes
6/2 ... yes
6/3 ... yes
6/4 ... yes
6/5 ... yes
6/6 ... yes
6/7 ... yes
4/8 ... yes
6/9 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.5.3)
Git version >= 2.18.0 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 8


Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished