API: don't allow merged PRs to be reopened (#17271)

routers/api/v1/repo/issue.go

@@ -752,6 +752,15 @@ func EditIssue(ctx *context.APIContext) {
 		}
 	}
 	if form.State != nil {
+		if issue.IsPull {
+			if pr, err := issue.GetPullRequest(); err != nil {
+				ctx.Error(http.StatusInternalServerError, "GetPullRequest", err)
+				return
+			} else if pr.HasMerged {
+				ctx.Error(http.StatusPreconditionFailed, "MergedPRState", "cannot change state of this pull request, it was already merged")
+				return
+			}
+		}
 		issue.IsClosed = api.StateClosed == api.StateType(*form.State)
 	}
 	statusChangeComment, titleChanged, err := models.UpdateIssueByAPI(issue, ctx.User)

routers/api/v1/repo/pull.go

@@ -584,6 +584,10 @@ func EditPullRequest(ctx *context.APIContext) {
 	}
 
 	if form.State != nil {
+		if pr.HasMerged {
+			ctx.Error(http.StatusPreconditionFailed, "MergedPRState", "cannot change state of this pull request, it was already merged")
+			return
+		}
 		issue.IsClosed = api.StateClosed == api.StateType(*form.State)
 	}
 	statusChangeComment, titleChanged, err := models.UpdateIssueByAPI(issue, ctx.User)
@@ -605,7 +609,7 @@ func EditPullRequest(ctx *context.APIContext) {
 	}
 
 	// change pull target branch
-	if len(form.Base) != 0 && form.Base != pr.BaseBranch {
+	if !pr.HasMerged && len(form.Base) != 0 && form.Base != pr.BaseBranch {
 		if !ctx.Repo.GitRepo.IsBranchExist(form.Base) {
 			ctx.Error(http.StatusNotFound, "NewBaseBranchNotExist", fmt.Errorf("new base '%s' not exist", form.Base))
 			return