default_branch value is ignored when creating a project via API

Summary

default_branch value is ignored when creating a project via Projects API

Steps to reproduce

Create a project via API using the similar command:

curl --request POST --header "PRIVATE-TOKEN: ***" -d '{ "name": "project-test001", "initialize_with_readme": "true", "default_branch": "stable" }' -H "Content-Type: application/json" "https://gitlabhostname.tld/api/v4/projects/"

What is the current bug behavior?

Default branch defined via default_branch is not created and selected as default.

What is the expected correct behavior?

Default branch defined via default_branch should be created and selected as default.

Relevant logs and/or screenshots

n/a

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:     Debian 8.10
Proxy:      no
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:    11.6.3-ee
Revision:   76c33c6
Directory:  /opt/gitlab/embedded/service/gitlab-rails
DB Adapter: postgresql
DB Version: 9.6.11
URL:        https://gitlabhost.tld
HTTP Clone URL: https://gitlabhost.tld/some-group/some-project.git
SSH Clone URL:  git@gitlabhost.tld:some-group/some-project.git
Elasticsearch:  no
Geo:        no
Using LDAP: no
Using Omniauth: yes
Omniauth Providers: google_oauth2, gitlab
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 ...
...
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: ...
1/13 ... yes
1/15 ... yes
1/17 ... yes
1/19 ... yes
8/28 ... yes
1/33 ... yes
1/38 ... yes
1/48 ... yes
15/49 ... yes
1/50 ... yes
1/51 ... yes
27/52 ... yes
1/53 ... yes
1/57 ... yes
1/69 ... yes
15/71 ... yes
27/72 ... yes
2/73 ... yes
1/74 ... yes
1/75 ... yes
1/77 ... yes
15/78 ... yes
1/79 ... yes
1/80 ... yes
1/81 ... yes
1/82 ... yes
1/83 ... yes
1/84 ... 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: ... 7
Elasticsearch version 5.6 - 6.x? ... skipped (elasticsearch is disabled)
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished

Possible fixes

The workaround is to use 3 API requests:

• create a project:

curl --request POST --header "PRIVATE-TOKEN: ***" -d '{ "name": "project-test001", "initialize_with_readme": "true"}' -H "Content-Type: application/json" "https://gitlabhostname.tld/api/v4/projects/"
create a new branch:

• create a branch:

curl --request POST --header "PRIVATE-TOKEN: ***" -H "Content-Type: application/json" "https://gitlabhostname.tld/api/v4/projects/ID/repository/branches?branch=new-branch&ref=master"
change the default branch to the newly created branch:

• update default branch:

curl --request PUT --header "PRIVATE-TOKEN: ***" -H "Content-Type: application/json" "https://gitlabhostname.tld/api/v4/projects/ID?default_branch=new-branch"

Basically, it looks like a doc bug, and probably we should not specify default_branch in the list of allowed parameters for create project API as a new project does not have any branches expect the default master branch.