Review updates and cleanupce-57402-add-issues-statistics-api-endpoints

* Cleaned issues and issues_statistics docs
* Renamed param with_labels_data to with_labels_details
* Added spec for N+1 check when retrieving labels from issue
* Refactoed CheckAssigneesCount validation class

2 files changed, 28 insertions, 41 deletions

diff --git a/doc/api/issues.md b/doc/api/issues.md
index 936caef7601..4fb3626f637 100644
--- a/doc/api/issues.md
+++ b/doc/api/issues.md
@@ -39,7 +39,7 @@ GET /issues?confidential=true
 | ------------------- | ---------------- | ---------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `state`             | string           | no         | Return `all` issues or just those that are `opened` or `closed`                                                                                       |
 | `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
-| `with_labels_data`  | Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
+| `with_labels_details`| Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.                             |
 | `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `created_by_me`<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
 | `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. _([Introduced][ce-13004] in GitLab 9.5)_ |
@@ -170,7 +170,7 @@ GET /groups/:id/issues?confidential=true
 | `id`                | integer/string   | yes        | The ID or [URL-encoded path of the group](README.md#namespaced-path-encoding) owned by the authenticated user                 |
 | `state`             | string           | no         | Return all issues or just those that are `opened` or `closed`                                                                 |
 | `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
-| `with_labels_data`  | Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
+| `with_labels_details`| Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
 | `iids[]`            | Array[integer]   | no         | Return only the issues having the given `iid`                                                                                 |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.       |
 | `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
@@ -301,7 +301,7 @@ GET /projects/:id/issues?confidential=true
 | `iids[]`            | Array[integer]   | no         | Return only the milestone having the given `iid`                                                                              |
 | `state`             | string           | no         | Return all issues or just those that are `opened` or `closed`                                                                 |
 | `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
-| `with_labels_data`  | Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
+| `with_labels_details`| Boolean          | no         | If `true`, response will return more details for each label in labels field: `:name`, `:color`, `:description`, `:text_color`. Default is `false`. |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.       |
 | `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
 | `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. _([Introduced][ce-13004] in GitLab 9.5)_ |
diff --git a/doc/api/issues_statistics.md b/doc/api/issues_statistics.md
index 1eeb1338104..82bc9c142cc 100644
--- a/doc/api/issues_statistics.md
+++ b/doc/api/issues_statistics.md
@@ -28,14 +28,14 @@ GET /issues_statistics?confidential=true
 
 | Attribute           | Type             | Required   | Description                                                                                                                                         |
 | ------------------- | ---------------- | ---------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
+| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.                             |
-| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `created_by_me`<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
-| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `author_username`   | string           | no         | Return issues created by the given `username`. Simillar to `author_id` and mutually exclusive with `author_id`. |
-| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Simillar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
-| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. _([Introduced][ce-14016] in GitLab 10.0)_ |
+| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `created_by_me` |
+| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. |
+| `author_username`   | string           | no         | Return issues created by the given `username`. Similar to `author_id` and mutually exclusive with `author_id`. |
+| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. |
+| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Similar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
+| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. |
 | `iids[]`            | Array[integer]   | no         | Return only the issues having the given `iid`                                                                                                       |
 | `search`            | string           | no         | Search issues against their `title` and `description`                                                                                               |
 | `in`                | string           | no         | Modify the scope of the `search` attribute. `title`, `description`, or a string joining them with comma. Default is `title,description`             |
@@ -63,13 +63,9 @@ Example response:
 }
 ```
 
-**Note**: `assignee` column is deprecated, now we show it as a single-sized array `assignees` to conform to the GitLab EE API.
+## Get group issues statistics
 
-**Note**: The `closed_by` attribute was [introduced in GitLab 10.6][ce-17042]. This value will only be present for issues which were closed after GitLab 10.6 and when the user account that closed the issue still exists.
-
-## List group issues
-
-Get a list of a group's issues.
+Gets issues count statistics for given group.
 
 ```
 GET /groups/:id/issues_statistics
@@ -89,15 +85,15 @@ GET /groups/:id/issues_statistics?confidential=true
 | Attribute           | Type             | Required   | Description                                                                                                                   |
 | ------------------- | ---------------- | ---------- | ----------------------------------------------------------------------------------------------------------------------------- |
 | `id`                | integer/string   | yes        | The ID or [URL-encoded path of the group](README.md#namespaced-path-encoding) owned by the authenticated user                 |
-| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
+| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. |
 | `iids[]`            | Array[integer]   | no         | Return only the issues having the given `iid`                                                                                 |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.       |
-| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
-| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `author_username`   | string           | no         | Return issues created by the given `username`. Simillar to `author_id` and mutually exclusive with `author_id`. |
-| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Simillar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
-| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. _([Introduced][ce-14016] in GitLab 10.0)_ |
+| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. |
+| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. |
+| `author_username`   | string           | no         | Return issues created by the given `username`. Similar to `author_id` and mutually exclusive with `author_id`. |
+| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. |
+| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Similar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
+| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. |
 | `search`            | string           | no         | Search group issues against their `title` and `description`                                                                   |
 | `created_after`     | datetime         | no         | Return issues created on or after the given time                                                                              |
 | `created_before`    | datetime         | no         | Return issues created on or before the given time                                                                             |
@@ -123,13 +119,9 @@ Example response:
 }
 ```
 
-**Note**: `assignee` column is deprecated, now we show it as a single-sized array `assignees` to conform to the GitLab EE API.
-
-**Note**: The `closed_by` attribute was [introduced in GitLab 10.6][ce-17042]. This value will only be present for issues which were closed after GitLab 10.6 and when the user account that closed the issue still exists.
-
-## List project issues
+## Get project issues statistics
 
-Get a list of a project's issues.
+Gets issues count statistics for given project.
 
 ```
 GET /projects/:id/issues_statistics
@@ -150,14 +142,14 @@ GET /projects/:id/issues_statistics?confidential=true
 | ------------------- | ---------------- | ---------- | ----------------------------------------------------------------------------------------------------------------------------- |
 | `id`                | integer/string   | yes        | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user               |
 | `iids[]`            | Array[integer]   | no         | Return only the milestone having the given `iid`                                                                              |
-| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. `No+Label` (Deprecated) lists all issues with no labels. Predefined names are case-insensitive. |
+| `labels`            | string           | no         | Comma-separated list of label names, issues must have all labels to be returned. `None` lists all issues with no labels. `Any` lists all issues with at least one label. |
 | `milestone`         | string           | no         | The milestone title. `None` lists all issues with no milestone. `Any` lists all issues that have an assigned milestone.       |
-| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13004] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
-| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `author_username`   | string           | no         | Return issues created by the given `username`. Simillar to `author_id` and mutually exclusive with `author_id`. |
-| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. _([Introduced][ce-13004] in GitLab 9.5)_ |
-| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Simillar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
-| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. _([Introduced][ce-14016] in GitLab 10.0)_ |
+| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. |
+| `author_id`         | integer          | no         | Return issues created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`. |
+| `author_username`   | string           | no         | Return issues created by the given `username`. Similar to `author_id` and mutually exclusive with `author_id`. |
+| `assignee_id`       | integer          | no         | Return issues assigned to the given user `id`. Mutually exclusive with `assignee_username`. `None` returns unassigned issues. `Any` returns issues with an assignee. |
+| `assignee_username` | Array[String]    | no         | Return issues assigned to the given `username`. Similar to `assignee_id` and mutually exclusive with `assignee_id`. In CE version `assignee_username` array should only contain a single value or an invalid param error will be returned otherwise. |
+| `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. |
 | `search`            | string           | no         | Search project issues against their `title` and `description`                                                                 |
 | `created_after`     | datetime         | no         | Return issues created on or after the given time                                                                              |
 | `created_before`    | datetime         | no         | Return issues created on or before the given time                                                                             |
@@ -183,8 +175,3 @@ Example response:
   }
 }
 ```
-
-**Note**: `assignee` column is deprecated, now we show it as a single-sized array `assignees` to conform to the GitLab EE API.
-
-**Note**: The `closed_by` attribute was [introduced in GitLab 10.6][ce-17042]. This value will only be present for issues which were closed after GitLab 10.6 and when the user account that closed the issue still exists.
-