Add get-an-issue-comment API endpoint (#2536)

src/main/scala/gitbucket/core/controller/api/ApiIssueCommentControllerBase.scala

@@ -35,9 +35,19 @@ trait ApiIssueCommentControllerBase extends ControllerBase {
    */
 
   /*
-   * iii. Get a single comment
-   * https://developer.github.com/v3/issues/comments/#get-a-single-comment
+   * iii. Get an issue comment
+   * https://docs.github.com/en/rest/reference/issues#get-an-issue-comment
    */
+  get("/api/v3/repos/:owner/:repository/issues/comments/:id")(referrersOnly { repository =>
+    val commentId = params("id").toInt
+    getCommentForApi(repository.owner, repository.name, commentId) match {
+      case Some((issueComment, user, issue)) =>
+        JsonFormat(
+          ApiComment(issueComment, RepositoryName(repository), issue.issueId, ApiUser(user), issue.isPullRequest)
+        )
+      case _ => NotFound()
+    }
+  })
 
   /*
    * iv. Create a comment

src/main/scala/gitbucket/core/service/IssuesService.scala

@@ -71,6 +71,20 @@ trait IssuesService {
     else None
   }
 
+  def getCommentForApi(owner: String, repository: String, commentId: Int)(
+    implicit s: Session
+  ): Option[(IssueComment, Account, Issue)] =
+    IssueComments
+      .filter(_.byRepository(owner, repository))
+      .filter(_.commentId === commentId)
+      .filter(_.action inSetBind Set("comment", "close_comment", "reopen_comment"))
+      .join(Accounts)
+      .on { case t1 ~ t2 => t1.commentedUserName === t2.userName }
+      .join(Issues)
+      .on { case t1 ~ t2 ~ t3 => t3.byIssue(t1.userName, t1.repositoryName, t1.issueId) }
+      .map { case t1 ~ t2 ~ t3 => (t1, t2, t3) }
+      .firstOption
+
   def getIssueLabels(owner: String, repository: String, issueId: Int)(implicit s: Session): List[Label] = {
     IssueLabels
       .join(Labels)