pr merge: pull after switching branches (#4748)

git/git.go

@@ -307,6 +307,19 @@ func CheckoutBranch(branch string) error {
 	return run.PrepareCmd(configCmd).Run()
 }
 
+// pull changes from remote branch without version history
+func Pull(remote, branch string) error {
+	pullCmd, err := GitCommand("pull", "--ff-only", remote, branch)
+	if err != nil {
+		return err
+	}
+
+	pullCmd.Stdout = os.Stdout
+	pullCmd.Stderr = os.Stderr
+	pullCmd.Stdin = os.Stdin
+	return run.PrepareCmd(pullCmd).Run()
+}
+
 func parseCloneArgs(extraArgs []string) (args []string, target string) {
 	args = extraArgs
 

pkg/cmd/pr/merge/merge.go

@@ -8,8 +8,10 @@ import (
 	"github.com/AlecAivazis/survey/v2"
 	"github.com/MakeNowJust/heredoc"
 	"github.com/cli/cli/v2/api"
+	"github.com/cli/cli/v2/context"
 	"github.com/cli/cli/v2/git"
 	"github.com/cli/cli/v2/internal/config"
+	"github.com/cli/cli/v2/internal/ghrepo"
 	"github.com/cli/cli/v2/pkg/cmd/pr/shared"
 	"github.com/cli/cli/v2/pkg/cmdutil"
 	"github.com/cli/cli/v2/pkg/iostreams"
@@ -26,6 +28,7 @@ type MergeOptions struct {
 	HttpClient func() (*http.Client, error)
 	IO         *iostreams.IOStreams
 	Branch     func() (string, error)
+	Remotes    func() (context.Remotes, error)
 
 	Finder shared.PRFinder
 
@@ -51,6 +54,7 @@ func NewCmdMerge(f *cmdutil.Factory, runF func(*MergeOptions) error) *cobra.Comm
 		IO:         f.IOStreams,
 		HttpClient: f.HttpClient,
 		Branch:     f.Branch,
+		Remotes:    f.Remotes,
 	}
 
 	var (
@@ -333,10 +337,16 @@ func mergeRun(opts *MergeOptions) error {
 			if err != nil {
 				return err
 			}
+
 			err = git.CheckoutBranch(branchToSwitchTo)
 			if err != nil {
 				return err
 			}
+
+			err := pullLatestChanges(opts, baseRepo, branchToSwitchTo)
+			if err != nil {
+				fmt.Fprintf(opts.IO.ErrOut, "%s warning: not posible to fast-forward to: %q\n", cs.WarningIcon(), branchToSwitchTo)
+			}
 		}
 
 		if err := git.DeleteLocalBranch(pr.HeadRefName); err != nil {
@@ -365,6 +375,25 @@ func mergeRun(opts *MergeOptions) error {
 	return nil
 }
 
+func pullLatestChanges(opts *MergeOptions, repo ghrepo.Interface, branch string) error {
+	remotes, err := opts.Remotes()
+	if err != nil {
+		return err
+	}
+
+	baseRemote, err := remotes.FindByRepo(repo.RepoOwner(), repo.RepoName())
+	if err != nil {
+		return err
+	}
+
+	err = git.Pull(baseRemote.Name, branch)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func mergeMethodSurvey(baseRepo *api.Repository) (PullRequestMergeMethod, error) {
 	type mergeOption struct {
 		title  string

pkg/cmd/pr/merge/merge_test.go

@@ -13,6 +13,8 @@ import (
 
 	"github.com/MakeNowJust/heredoc"
 	"github.com/cli/cli/v2/api"
+	"github.com/cli/cli/v2/context"
+	"github.com/cli/cli/v2/git"
 	"github.com/cli/cli/v2/internal/ghrepo"
 	"github.com/cli/cli/v2/internal/run"
 	"github.com/cli/cli/v2/pkg/cmd/pr/shared"
@@ -223,6 +225,16 @@ func runCommand(rt http.RoundTripper, branch string, isTTY bool, cli string) (*t
 		Branch: func() (string, error) {
 			return branch, nil
 		},
+		Remotes: func() (context.Remotes, error) {
+			return []*context.Remote{
+				{
+					Remote: &git.Remote{
+						Name: "origin",
+					},
+					Repo: ghrepo.New("OWNER", "REPO"),
+				},
+			}, nil
+		},
 	}
 
 	cmd := NewCmdMerge(factory, nil)
@@ -432,6 +444,7 @@ func TestPrMerge_deleteBranch(t *testing.T) {
 	cs.Register(`git checkout master`, 0, "")
 	cs.Register(`git rev-parse --verify refs/heads/blueberries`, 0, "")
 	cs.Register(`git branch -D blueberries`, 0, "")
+	cs.Register(`git pull --ff-only`, 0, "")
 
 	output, err := runCommand(http, "blueberries", true, `pr merge --merge --delete-branch`)
 	if err != nil {
@@ -715,6 +728,7 @@ func TestPrMerge_alreadyMerged(t *testing.T) {
 	cs.Register(`git checkout master`, 0, "")
 	cs.Register(`git rev-parse --verify refs/heads/blueberries`, 0, "")
 	cs.Register(`git branch -D blueberries`, 0, "")
+	cs.Register(`git pull --ff-only`, 0, "")
 
 	as, surveyTeardown := prompt.InitAskStubber()
 	defer surveyTeardown()
@@ -850,6 +864,7 @@ func TestPRMerge_interactiveWithDeleteBranch(t *testing.T) {
 	cs.Register(`git checkout master`, 0, "")
 	cs.Register(`git rev-parse --verify refs/heads/blueberries`, 0, "")
 	cs.Register(`git branch -D blueberries`, 0, "")
+	cs.Register(`git pull --ff-only`, 0, "")
 
 	as, surveyTeardown := prompt.InitAskStubber()
 	defer surveyTeardown()