Find PRs using @{push}

When using a triangular workflow with push.default = current and
upstream being set to the target branch [1], or a similar but simpler
central workflow [2], we should use @{push} instead to locate the remote
branch.

In fact, @{push} covers most cases in push.default = upstream too. The
branch.<name>.merge is probably only needed when using RemoteURL and
different remote / local branch names.

[1] cli#575 (comment)
[2] tpope/vim-fugitive#1172 (comment)

git/client.go

@@ -355,6 +355,9 @@ func (c *Client) ReadBranchConfig(ctx context.Context, branch string) (cfg Branc
 			cfg.MergeRef = parts[1]
 		}
 	}
+	if out, err = c.revParse(ctx, "--verify", "--quiet", "--abbrev-ref", branch+"@{push}"); err == nil {
+		cfg.Push = strings.TrimSuffix(string(out), "\n")
+	}
 	return
 }
 

git/objects.go

@@ -74,4 +74,5 @@ type BranchConfig struct {
 	RemoteName string
 	RemoteURL  *url.URL
 	MergeRef   string
+	Push       string
 }

pkg/cmd/pr/shared/finder.go

@@ -261,7 +261,9 @@ func (f *finder) parseCurrentBranch() (string, int, error) {
 	}
 
 	if branchOwner != "" {
-		if strings.HasPrefix(branchConfig.MergeRef, "refs/heads/") {
+		if branchConfig.Push != "" {
+			prHeadRef = strings.TrimPrefix(branchConfig.Push, branchConfig.RemoteName+"/")
+		} else if strings.HasPrefix(branchConfig.MergeRef, "refs/heads/") {
 			prHeadRef = strings.TrimPrefix(branchConfig.MergeRef, "refs/heads/")
 		}
 		// prepend `OWNER:` if this branch is pushed to a fork

pkg/cmd/pr/shared/finder_test.go

@@ -232,8 +232,17 @@ func TestFind(t *testing.T) {
 					return "blueberries", nil
 				},
 				branchConfig: func(branch string) (c git.BranchConfig) {
+					c.MergeRef = "refs/heads/blueberries"
+					c.RemoteName = "origin"
+					c.Push = "origin/blueberries"
 					return
 				},
+				remotesFn: func() (context.Remotes, error) {
+					return context.Remotes{{
+						Remote: &git.Remote{Name: "origin"},
+						Repo:   ghrepo.New("OWNER", "REPO"),
+					}}, nil
+				},
 			},
 			httpStub: func(r *httpmock.Registry) {
 				r.Register(
@@ -318,6 +327,7 @@ func TestFind(t *testing.T) {
 				branchConfig: func(branch string) (c git.BranchConfig) {
 					c.MergeRef = "refs/heads/blue-upstream-berries"
 					c.RemoteName = "origin"
+					c.Push = "origin/blue-upstream-berries"
 					return
 				},
 				remotesFn: func() (context.Remotes, error) {

pkg/cmd/pr/status/status.go

@@ -209,7 +209,9 @@ func prSelectorForCurrentBranch(gitClient *git.Client, baseRepo ghrepo.Interface
 	}
 
 	if branchOwner != "" {
-		if strings.HasPrefix(branchConfig.MergeRef, "refs/heads/") {
+		if branchConfig.Push != "" {
+			selector = strings.TrimPrefix(branchConfig.Push, branchConfig.RemoteName+"/")
+		} else if strings.HasPrefix(branchConfig.MergeRef, "refs/heads/") {
 			selector = strings.TrimPrefix(branchConfig.MergeRef, "refs/heads/")
 		}
 		// prepend `OWNER:` if this branch is pushed to a fork