This is actually a little worse than I thought, the compute profile is not applied even if there is a compute profile in the host group.

Steps to reproduce:
1. Create a new host
2. Select a host group with a compute profile attached
3. Select a compute resource to deploy onto (VMware in our case)

Results: A compute profile is selected and greyed out, indicating it has been inherited and applied. However when you navigate to the "Virtual Machine" tab on the new host screen, it is apparent that the compute profile has not actually been applied.

Expected results: The compute profile field should be applied when it is inherited from the host group.

Expected results: The compute profile field should not be selected and left active for the user to make a selection

It appears that #9591 removed the "include_blank" attribute on the compute_profile field, so there's no longer any way to have no compute profile. Adding this back appears, on the surface, to fix it.

This is actually a little worse than I thought, the compute profile is not applied even if there is a compute profile in the host group.

I can't reproduce this aspect on a libvirt compute resource, at least. The selection of a compute resource should trigger this AJAX request:

Started POST "/hosts/compute_resource_selected"

If you can enable SQL debugging (http://theforeman.org/manuals/1.10/index.html#7.2Debugging) then you should also see lookups of compute_attributes, e.g.

ComputeAttribute Load (0.1ms)  SELECT "compute_attributes".* FROM "compute_attributes" WHERE "compute_attributes"."compute_resource_id" = 1 AND "compute_attributes"."compute_profile_id" = 4 LIMIT 1

There is a workaround for the issue for the meantime:

Select the hostgroup first, then the fields will be set to "inherit", and the system will behave as expected.

Problems that I have found in code:

1. AJAX requests are passing empty values for inherited fields (environment, compute_profile, puppet_proxy e.t.c), which interferes with the normal flow of hostgroup selection.
2. Hostgroup selection changes only the compute_profile, but does not affect the actual values of the "Virtual machine" tab.

Test cases:

1. With locations organizations enabled: * go to /hosts/new * Select organization (AJAX will be fired) * Select a hostgroup
Expected: Environment field disabled with a value from the hostgroup shown
Actual: Environment field enabled, the value remains empty.

Didn't check it actually, but selection of compute resource in step 2 should lead to the same result.

2. * Create a hostgroup with a compute profile that is not the first one (if you have 1-Small, 2-Medium, 3-Large use large or medium) * Go to /hosts/new * Select a compute resource * Ensure that properties in "Virtual machine" tab are from the first compute profile * Select the hostgroup from the first step * Go to "Virtual machine" tab
Expected: properties are set according to large/medium profile.
Actual: properties are set according to small (first) profile.