Variable propagation fails with include_role

POC of a bug in ansible 2.7.1

A variable in a role propagates in transitively included roles (include_role) only until level 4. After that the variable becomes undefined

After executing the included playbook, role4 displays the default value propageted from role2, instead of the variable value "inherited" from role1

Expected behaviour: execution of role4's debug message should display value instead of role2 default

$ ansible-playbook playbook.yml
[...]

TASK [role1 : debug] ******************************************************************************************************************************************************************
ok: [127.0.0.1] => {
    "msg": "var: [value]"
}

TASK [include_role : role2] ***********************************************************************************************************************************************************

TASK [role2 : debug] ******************************************************************************************************************************************************************
ok: [127.0.0.1] => {
    "msg": "var: [value]"
}

TASK [include_role : role3] ***********************************************************************************************************************************************************

TASK [role3 : debug] ******************************************************************************************************************************************************************
ok: [127.0.0.1] => {
    "msg": "var: [value]"
}

TASK [include_role : role4] ***********************************************************************************************************************************************************

TASK [role4 : debug] ******************************************************************************************************************************************************************
ok: [127.0.0.1] => {
    "msg": "var: [role2 default]"
}

It works as intended if:

• the variable is in the playbook
• the variable in in hosts_vars or group_vars
• if the playbook uses import_role
• if the playbook uses roles: instead of tasks:

Update 2018.11.25

Marked as duplicate ansible/ansible#48371 (comment)