Merge branch '2489-soft-delete-issues' into 'master'

Soft delete issuables

Fixes #2489 

What still needs to happen: research on the indexes, the gem suggests a [lot of changes](https://github.com/rubysherpas/paranoia#about-indexes) though this is probably a good idea to discuss and I'm unsure on the impact of an omnibus upgrade as I suspect creating about 10 new indexes has a large impact on the downtime.

TODO: 
- [x] Also group owners can ***soft*** delete
- [x] Button should be hidden

See merge request !2982

2 files changed, 32 insertions, 5 deletions

diff --git a/doc/api/issues.md b/doc/api/issues.md
index 9e704648b25..18d64c41986 100644
--- a/doc/api/issues.md
+++ b/doc/api/issues.md
@@ -326,17 +326,25 @@ Example response:
 }
 ```
 
-## Delete existing issue (**Deprecated**)
+## Delete an issue
 
-This call is deprecated and returns a `405 Method Not Allowed` error if called.
-An issue gets now closed and is done by calling
-`PUT /projects/:id/issues/:issue_id` with the parameter `state_event` set to
-`close`. See [edit issue](#edit-issue) for more details.
+Only for admins and project owners. Soft deletes the issue in question.
+If the operation is successful, a status code `200` is returned. In case you cannot
+destroy this issue, or it is not present, code `404` is given.
 
 ```
 DELETE /projects/:id/issues/:issue_id
 ```
 
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`            | integer | yes | The ID of a project |
+| `issue_id`      | integer | yes | The ID of a project's issue |
+
+```bash
+curl -X DELETE -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/4/issues/85
+```
+
 ## Comments on issues
 
 Comments are done via the [notes](notes.md) resource.
diff --git a/doc/api/merge_requests.md b/doc/api/merge_requests.md
index 5c527d55481..b20a6300b7a 100644
--- a/doc/api/merge_requests.md
+++ b/doc/api/merge_requests.md
@@ -380,6 +380,25 @@ Parameters:
 If the operation is successful, 200 and the updated merge request is returned.
 If an error occurs, an error number and a message explaining the reason is returned.
 
+## Delete a merge request
+
+Only for admins and project owners. Soft deletes the merge request in question.
+If the operation is successful, a status code `200` is returned. In case you cannot
+destroy this merge request, or it is not present, code `404` is given.
+
+```
+DELETE /projects/:id/merge_requests/:merge_request_id
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`            | integer | yes | The ID of a project |
+| `merge_request_id` | integer | yes | The ID of a project's merge request |
+
+```bash
+curl -X DELETE -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/4/merge_request/85
+```
+
 ## Accept MR
 
 Merge changes submitted with MR using this API.