Change type of a workitem

[DhritiShikhar]

As per discussion with @kwk and @jarifibrahim

Description

Implement the backend support for changing the type of a workitem.

Steps

1. To change workitemtype of a workitem, send a PATCH request to the workitem:

2. Check if the user is allowed to change the workitem. Only creator and space owner can change the type as of now.

3. Iterate over the fields of original workitem.

Case 1

Both original workitem and new workitem have the same field name and field type. In this case, the data is retained.

Case 2

New workitem has a field which original workitem does not have. In this case, the new workitem gets empty value (or default values; refer #2160).

Case 3

Original workitem has an extra field which the new workitem does not have. To preserve the data, we simply append the data to description field of workitem.

Audit Trail

Audit Trail should contain a record of change of work item type.

[sbose78]

Sounds like a plan!

[jarifibrahim]

Here's how the migration of workitem from Type A to Type B will be performed.

1. At the controller level, check if the update is a type update. If so, check if the user is space owner or workitem creator.
2. Perform Migration if user is authorized to do so at the repository level
   1. Find the diff of fields in Type A and Type B. Remove the diff from Type A.
   2. The resultant set of fields in Type A is a subset of fields in Type B. Update all matching fields in Type A and Type B with values of Type A.
   3. Append the diff (with field name and type) to the Description of the workitem

[jarifibrahim]

Consider the following topology
Epic -> Story -> Task
When the user changes Epic to Bug, we will have Bug -> Story -> Task .This is a possible side effect of the type change.

[kwk]

Consider the following topology
Epic -> Story -> Task
When the user changes Epic to Bug, we will have Bug -> Story -> Task .This is a possible side effect of the type change.

@jarifibrahim yes, this is expected.

[jarifibrahim]

Fixed via #2202