Store each branch's push destination in the branch model

To push a branch other than the checked-out one, lazygit has to name the
remote and the remote branch in the push command; a bare `git push` only
works for the current branch. The upstream isn't always the right
destination. In a triangular workflow the branch is pushed to a
different remote than it pulls from, and with push.default set to
"current" it goes to a branch of the same name whatever the upstream is
called.

Read the destination from git instead of working it out from the config.
The %(push) field of for-each-ref names the remote-tracking ref that a
push would update, taking push.default, remote.pushDefault and
branch.<name>.pushRemote into account. It is also the ref that the
push:track counts are computed against, so the force-push detection and
the destination agree. The field is available since git 2.5, well before
the oldest version lazygit supports.

Nothing uses the new fields yet.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

pkg/commands/git_commands/branch_loader.go

@@ -349,6 +349,7 @@ var branchFields = []string{
 	"upstream:short",
 	"upstream:track",
 	"push:track",
+	"push",
 	"subject",
 	"objectname",
 	"committerdate:unix",
@@ -361,13 +362,15 @@ func obtainBranch(split []string, storeCommitDateAsRecency bool) (*models.Branch
 	upstreamName := split[2]
 	track := split[3]
 	pushTrack := split[4]
-	subject := split[5]
-	commitHash := split[6]
-	commitDate := split[7]
+	pushRef := split[5]
+	subject := split[6]
+	commitHash := split[7]
+	commitDate := split[8]
 
 	name := strings.TrimPrefix(fullName, "heads/")
 	aheadForPull, behindForPull, gone := parseUpstreamInfo(upstreamName, track)
 	aheadForPush, behindForPush, _ := parseUpstreamInfo(upstreamName, pushTrack)
+	pushRemote, pushBranch := parsePushDestination(pushRef)
 
 	recency := ""
 	if storeCommitDateAsRecency {
@@ -383,6 +386,8 @@ func obtainBranch(split []string, storeCommitDateAsRecency bool) (*models.Branch
 		BehindForPull: behindForPull,
 		AheadForPush:  aheadForPush,
 		BehindForPush: behindForPush,
+		PushRemote:    pushRemote,
+		PushBranch:    pushBranch,
 		UpstreamGone:  gone,
 		Head:          headMarker == "*",
 		Subject:       subject,
@@ -410,6 +415,25 @@ func parseUpstreamInfo(upstreamName string, track string) (string, string, bool)
 	return ahead, behind, false
 }
 
+// Splits the remote-tracking ref that the %(push) field names, e.g.
+// refs/remotes/origin/main, into the remote and the remote branch. Returns
+// empty strings if the field is empty because git has no push destination for
+// the branch, or if the ref isn't under refs/remotes/.
+func parsePushDestination(pushRef string) (string, string) {
+	remoteAndBranch, ok := strings.CutPrefix(pushRef, "refs/remotes/")
+	if !ok {
+		return "", ""
+	}
+
+	// Remote names can't contain slashes, so the first one ends the remote name
+	remote, branch, ok := strings.Cut(remoteAndBranch, "/")
+	if !ok {
+		return "", ""
+	}
+
+	return remote, branch
+}
+
 func parseDifference(track string, regexStr string) string {
 	re := regexp.MustCompile(regexStr)
 	match := re.FindStringSubmatch(track)

pkg/commands/git_commands/branch_loader_test.go

@@ -26,7 +26,7 @@ func TestObtainBranch(t *testing.T) {
 	scenarios := []scenario{
 		{
 			testName:                 "TrimHeads",
-			input:                    []string{"", "heads/a_branch", "", "", "", "subject", "123", timeStamp},
+			input:                    []string{"", "heads/a_branch", "", "", "", "", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: false,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",
@@ -41,7 +41,7 @@ func TestObtainBranch(t *testing.T) {
 		},
 		{
 			testName:                 "NoUpstream",
-			input:                    []string{"", "a_branch", "", "", "", "subject", "123", timeStamp},
+			input:                    []string{"", "a_branch", "", "", "", "", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: false,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",
@@ -56,7 +56,7 @@ func TestObtainBranch(t *testing.T) {
 		},
 		{
 			testName:                 "IsHead",
-			input:                    []string{"*", "a_branch", "", "", "", "subject", "123", timeStamp},
+			input:                    []string{"*", "a_branch", "", "", "", "", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: false,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",
@@ -71,7 +71,7 @@ func TestObtainBranch(t *testing.T) {
 		},
 		{
 			testName:                 "IsBehindAndAhead",
-			input:                    []string{"", "a_branch", "a_remote/a_branch", "[behind 2, ahead 3]", "[behind 2, ahead 3]", "subject", "123", timeStamp},
+			input:                    []string{"", "a_branch", "a_remote/a_branch", "[behind 2, ahead 3]", "[behind 2, ahead 3]", "refs/remotes/a_remote/a_branch", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: false,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",
@@ -79,6 +79,40 @@ func TestObtainBranch(t *testing.T) {
 				BehindForPull: "2",
 				AheadForPush:  "3",
 				BehindForPush: "2",
+				PushRemote:    "a_remote",
+				PushBranch:    "a_branch",
+				Head:          false,
+				Subject:       "subject",
+				CommitHash:    "123",
+			},
+		},
+		{
+			testName:                 "PushDestinationDiffersFromUpstream",
+			input:                    []string{"", "a_branch", "a_remote/a_branch", "[ahead 3]", "[ahead 5]", "refs/remotes/my_fork/feature/a_branch", "subject", "123", timeStamp},
+			storeCommitDateAsRecency: false,
+			expectedBranch: &models.Branch{
+				Name:          "a_branch",
+				AheadForPull:  "3",
+				BehindForPull: "0",
+				AheadForPush:  "5",
+				BehindForPush: "0",
+				PushRemote:    "my_fork",
+				PushBranch:    "feature/a_branch",
+				Head:          false,
+				Subject:       "subject",
+				CommitHash:    "123",
+			},
+		},
+		{
+			testName:                 "PushDestinationNotARemoteTrackingRef",
+			input:                    []string{"", "a_branch", "a_remote/a_branch", "", "", "refs/published/a_branch", "subject", "123", timeStamp},
+			storeCommitDateAsRecency: false,
+			expectedBranch: &models.Branch{
+				Name:          "a_branch",
+				AheadForPull:  "0",
+				BehindForPull: "0",
+				AheadForPush:  "0",
+				BehindForPush: "0",
 				Head:          false,
 				Subject:       "subject",
 				CommitHash:    "123",
@@ -86,7 +120,7 @@ func TestObtainBranch(t *testing.T) {
 		},
 		{
 			testName:                 "RemoteBranchIsGone",
-			input:                    []string{"", "a_branch", "a_remote/a_branch", "[gone]", "[gone]", "subject", "123", timeStamp},
+			input:                    []string{"", "a_branch", "a_remote/a_branch", "[gone]", "[gone]", "refs/remotes/a_remote/a_branch", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: false,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",
@@ -95,6 +129,8 @@ func TestObtainBranch(t *testing.T) {
 				BehindForPull: "?",
 				AheadForPush:  "?",
 				BehindForPush: "?",
+				PushRemote:    "a_remote",
+				PushBranch:    "a_branch",
 				Head:          false,
 				Subject:       "subject",
 				CommitHash:    "123",
@@ -102,7 +138,7 @@ func TestObtainBranch(t *testing.T) {
 		},
 		{
 			testName:                 "WithCommitDateAsRecency",
-			input:                    []string{"", "a_branch", "", "", "", "subject", "123", timeStamp},
+			input:                    []string{"", "a_branch", "", "", "", "", "subject", "123", timeStamp},
 			storeCommitDateAsRecency: true,
 			expectedBranch: &models.Branch{
 				Name:          "a_branch",

pkg/commands/models/branch.go

@@ -31,6 +31,13 @@ type Branch struct {
 	// 'git@github.com:tiwood/lazygit.git'
 	UpstreamRemote string
 	UpstreamBranch string
+	// The remote and the remote branch that `git push` would push this branch
+	// to, as git determines them from push.default, remote.pushDefault and
+	// branch.<name>.pushRemote. In a triangular workflow these differ from the
+	// upstream. Both are empty if git has no push destination for the branch,
+	// e.g. because push.default is "upstream" and the branch has no upstream.
+	PushRemote string
+	PushBranch string
 	// subject line in commit message
 	Subject string
 	// commit hash