Feature merge request beyond 20 (#551)

* feat(choose_merge_request): add per_page option for merge request fetching

Allow users to configure the number of merge requests fetched via the
`per_page` setting in `choose_merge_request`. Defaults to 100.

* Remove the per_page option and now fetch all merge request internally

* Implement merge request pagination using gitlab api

---------

Co-authored-by: Clement Hue <clement.hue@thetrainline.com>

Author: Clement-Hue

cmd/app/merge_requests.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"net/http"
+	"slices"
 
 	gitlab "gitlab.com/gitlab-org/api/client-go"
 )
@@ -35,23 +36,18 @@ func (a mergeRequestListerService) ServeHTTP(w http.ResponseWriter, r *http.Requ
 		payload.Scope = gitlab.Ptr("all")
 	}
 
-	payload.PerPage = 100
-	var mergeRequests []*gitlab.BasicMergeRequest
-	for nextPage := int64(1); nextPage != 0; {
-		payload.Page = nextPage
-		mrs, res, err := a.client.ListProjectMergeRequests(a.projectInfo.ProjectId, payload)
-		if err != nil {
-			handleError(w, err, "Failed to list merge requests", http.StatusInternalServerError)
-			return
-		}
+	payload.ListOptions = gitlab.ListOptions{
+		PerPage: 100,
+	}
 
-		if res.StatusCode >= 300 {
-			handleError(w, GenericError{r.URL.Path}, "Failed to list merge requests", res.StatusCode)
-			return
-		}
+	it, hasErr := gitlab.Scan(func(p gitlab.PaginationOptionFunc) ([]*gitlab.BasicMergeRequest, *gitlab.Response, error) {
+		return a.client.ListProjectMergeRequests(a.projectInfo.ProjectId, payload, p)
+	})
+	mergeRequests := slices.Collect(it)
 
-		mergeRequests = append(mergeRequests, mrs...)
-		nextPage = res.NextPage
+	if err := hasErr(); err != nil {
+		handleError(w, err, "Failed to list merge requests", http.StatusInternalServerError)
+		return
 	}
 
 	if len(mergeRequests) == 0 {

cmd/app/merge_requests_test.go

@@ -56,13 +56,13 @@ func TestMergeRequestHandler(t *testing.T) {
 	t.Run("Handles non-200s from Gitlab client", func(t *testing.T) {
 		request := makeRequest(t, http.MethodPost, "/merge_requests", testListMergeRequestsRequest)
 		svc := middleware(
-			mergeRequestListerService{testProjectData, fakeMergeRequestLister{testBase: testBase{status: http.StatusSeeOther}}},
+			mergeRequestListerService{testProjectData, fakeMergeRequestLister{testBase: testBase{errFromGitlab: true}}},
 			withPayloadValidation(methodToPayload{http.MethodPost: newPayload[gitlab.ListProjectMergeRequestsOptions]}),
 			withMethodCheck(http.MethodPost),
 		)
 		data, status := getFailData(t, svc, request)
-		checkNon200(t, data, "Failed to list merge requests", "/merge_requests")
-		assert(t, status, http.StatusSeeOther)
+		checkErrorFromGitlab(t, data, "Failed to list merge requests")
+		assert(t, status, http.StatusInternalServerError)
 	})
 	t.Run("Should handle not having any merge requests with 404", func(t *testing.T) {
 		request := makeRequest(t, http.MethodPost, "/merge_requests", testListMergeRequestsRequest)