Use upstream branch when opening pull requests (#2693)

- **PR Description**

Should probably solve #2691

- **Please check if the PR fulfills these requirements**

* [x] Cheatsheets are up-to-date (run `go run scripts/cheatsheet/main.go
generate`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [x] Docs (specifically `docs/Config.md`) have been updated if
necessary
* [x] You've read through your own file changes for silly mistakes etc

pkg/gui/controllers/branches_controller.go

@@ -318,7 +318,10 @@ func (self *BranchesController) promptToCheckoutWorktree(worktree *models.Worktr
 }
 
 func (self *BranchesController) handleCreatePullRequest(selectedBranch *models.Branch) error {
-	return self.createPullRequest(selectedBranch.Name, "")
+	if !selectedBranch.IsTrackingRemote() {
+		return self.c.ErrorMsg(self.c.Tr.PullRequestNoUpstream)
+	}
+	return self.createPullRequest(selectedBranch.UpstreamBranch, "")
 }
 
 func (self *BranchesController) handleCreatePullRequestMenu(selectedBranch *models.Branch) error {
@@ -678,7 +681,7 @@ func (self *BranchesController) createPullRequestMenu(selectedBranch *models.Bra
 			{
 				LabelColumns: fromToLabelColumns(branch.Name, self.c.Tr.DefaultBranch),
 				OnPress: func() error {
-					return self.createPullRequest(branch.Name, "")
+					return self.handleCreatePullRequest(branch)
 				},
 			},
 			{
@@ -686,7 +689,7 @@ func (self *BranchesController) createPullRequestMenu(selectedBranch *models.Bra
 				OnPress: func() error {
 					return self.c.Prompt(types.PromptOpts{
 						Title:               branch.Name + " →",
-						FindSuggestionsFunc: self.c.Helpers().Suggestions.GetBranchNameSuggestionsFunc(),
+						FindSuggestionsFunc: self.c.Helpers().Suggestions.GetRemoteBranchesSuggestionsFunc("/"),
 						HandleConfirm: func(targetBranchName string) error {
 							return self.createPullRequest(branch.Name, targetBranchName)
 						},
@@ -701,7 +704,10 @@ func (self *BranchesController) createPullRequestMenu(selectedBranch *models.Bra
 			&types.MenuItem{
 				LabelColumns: fromToLabelColumns(checkedOutBranch.Name, selectedBranch.Name),
 				OnPress: func() error {
-					return self.createPullRequest(checkedOutBranch.Name, selectedBranch.Name)
+					if !checkedOutBranch.IsTrackingRemote() || !selectedBranch.IsTrackingRemote() {
+						return self.c.ErrorMsg(self.c.Tr.PullRequestNoUpstream)
+					}
+					return self.createPullRequest(checkedOutBranch.UpstreamBranch, selectedBranch.UpstreamBranch)
 				},
 			},
 		)

pkg/i18n/english.go

@@ -221,6 +221,7 @@ type TranslationSet struct {
 	FwdNoUpstream                       string
 	FwdNoLocalUpstream                  string
 	FwdCommitsToPush                    string
+	PullRequestNoUpstream               string
 	ErrorOccurred                       string
 	NoRoom                              string
 	YouAreHere                          string
@@ -1019,6 +1020,7 @@ func EnglishTranslationSet() TranslationSet {
 		FwdNoUpstream:                       "Cannot fast-forward a branch with no upstream",
 		FwdNoLocalUpstream:                  "Cannot fast-forward a branch whose remote is not registered locally",
 		FwdCommitsToPush:                    "Cannot fast-forward a branch with commits to push",
+		PullRequestNoUpstream:               "Cannot open a pull request for a branch with no upstream",
 		ErrorOccurred:                       "An error occurred! Please create an issue at",
 		NoRoom:                              "Not enough room",
 		YouAreHere:                          "YOU ARE HERE",

pkg/integration/tests/branch/open_pull_request_no_upstream.go

@@ -0,0 +1,25 @@
+package branch
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var OpenPullRequestNoUpstream = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Open up a pull request with a missing upstream branch",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo:    func(shell *Shell) {},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().
+			Branches().
+			Focus().
+			Press(keys.Branches.CreatePullRequest)
+
+		t.ExpectPopup().Alert().
+			Title(Equals("Error")).
+			Content(Contains("Cannot open a pull request for a branch with no upstream")).
+			Confirm()
+	},
+})

pkg/integration/tests/test_list.go

@@ -40,6 +40,7 @@ var tests = []*components.IntegrationTest{
 	branch.Delete,
 	branch.DeleteRemoteBranchWithCredentialPrompt,
 	branch.DetachedHead,
+	branch.OpenPullRequestNoUpstream,
 	branch.OpenWithCliArg,
 	branch.Rebase,
 	branch.RebaseAbortOnConflict,