From 242a2ed6f6b17b3f93bde8196723abb879fc1711 Mon Sep 17 00:00:00 2001
From: Gary Holtz <gholtz@gitlab.com>
Date: Mon, 25 Mar 2024 08:14:44 +0000
Subject: [PATCH] feat(checkout): Fixing bug with private forks

---
 commands/mr/checkout/mr_checkout.go      | 19 ++++++--
 commands/mr/checkout/mr_checkout_test.go | 58 ++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 3 deletions(-)

diff --git a/commands/mr/checkout/mr_checkout.go b/commands/mr/checkout/mr_checkout.go
index 97c582ce..a83da626 100644
--- a/commands/mr/checkout/mr_checkout.go
+++ b/commands/mr/checkout/mr_checkout.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/MakeNowJust/heredoc"
 	"github.com/spf13/cobra"
+	"github.com/xanzy/go-gitlab"
 	"gitlab.com/gitlab-org/cli/api"
 	"gitlab.com/gitlab-org/cli/commands/cmdutils"
 	"gitlab.com/gitlab-org/cli/commands/mr/mrutils"
@@ -67,12 +68,24 @@ func NewCmdCheckout(f *cmdutils.Factory) *cobra.Command {
 				mrCheckoutCfg.branch = mr.SourceBranch
 			}
 
-			mrProject, err := api.GetProject(apiClient, mr.SourceProjectID)
+			var mrRef string
+			var mrProject *gitlab.Project
+
+			mrProject, err = api.GetProject(apiClient, mr.SourceProjectID)
 			if err != nil {
-				return err
+				// If we don't have access to the source project, let's try the target project
+				mrProject, err = api.GetProject(apiClient, mr.TargetProjectID)
+				if err != nil {
+					return err
+				} else {
+					// We found the target project, let's find the ref another way
+					mrRef = fmt.Sprintf("refs/merge-requests/%d/head", mr.IID)
+				}
+
+			} else {
+				mrRef = fmt.Sprintf("refs/heads/%s", mr.SourceBranch)
 			}
 
-			mrRef := fmt.Sprintf("refs/heads/%s", mr.SourceBranch)
 			fetchRefSpec := fmt.Sprintf("%s:%s", mrRef, mrCheckoutCfg.branch)
 			if err := git.RunCmd([]string{"fetch", mrProject.SSHURLToRepo, fetchRefSpec}); err != nil {
 				return err
diff --git a/commands/mr/checkout/mr_checkout_test.go b/commands/mr/checkout/mr_checkout_test.go
index a20ba9a7..74828d8e 100644
--- a/commands/mr/checkout/mr_checkout_test.go
+++ b/commands/mr/checkout/mr_checkout_test.go
@@ -122,6 +122,64 @@ func TestMrCheckout(t *testing.T) {
 				"git checkout feat-new-mr",
 			},
 		},
+		{
+			name:        "when a valid MR comes from a forked private project",
+			commandArgs: "123",
+			branch:      "main",
+			httpMocks: []httpMock{
+				{
+					http.MethodGet,
+					"/api/v4/projects/OWNER/REPO/merge_requests/123",
+					http.StatusOK,
+					`{
+							"id": 123,
+							"iid": 123,
+							"project_id": 3,
+							"source_project_id": 3,
+							"target_project_id": 4,
+							"title": "test mr title",
+							"description": "test mr description",
+							"allow_collaboration": false,
+							"state": "opened",
+							"source_branch":"feat-new-mr"
+							}`,
+				},
+				{
+					http.MethodGet,
+					"/api/v4/projects/4",
+					http.StatusOK,
+					`{
+							"id": 4,
+							"ssh_url_to_repo": "git@gitlab.com:OWNER/REPO.git"
+						}`,
+				},
+				{
+					http.MethodGet,
+					"/api/v4/projects/3",
+					http.StatusNotFound,
+					`{
+						"message":"404 Project Not Found"
+					}`,
+				},
+			},
+			shelloutStubs: []string{
+				"HEAD branch: master\n",
+				"\n",
+				"\n",
+				heredoc.Doc(`
+				deadbeef HEAD
+				deadb00f refs/remotes/upstream/feat-new-mr
+				deadbeef refs/remotes/origin/feat-new-mr
+				`),
+			},
+
+			expectedShellouts: []string{
+				"git fetch git@gitlab.com:OWNER/REPO.git refs/merge-requests/123/head:feat-new-mr",
+				"git config branch.feat-new-mr.remote git@gitlab.com:OWNER/REPO.git",
+				"git config branch.feat-new-mr.merge refs/merge-requests/123/head",
+				"git checkout feat-new-mr",
+			},
+		},
 		{
 			name:        "when a valid MR is checked out using MR id and specifying branch",
 			commandArgs: "123 --branch foo",