Correctly request force-pushing in triangular workflows

To determine whether we need to ask for force pushing, we need to query the push
branch rather than the upstream branch, in case they are not the same.

pkg/commands/models/branch.go

@@ -103,6 +103,10 @@ func (b *Branch) IsBehindForPull() bool {
 	return b.RemoteBranchStoredLocally() && b.BehindForPull != "0"
 }
 
+func (b *Branch) IsBehindForPush() bool {
+	return b.BehindForPush != "" && b.BehindForPush != "0"
+}
+
 // for when we're in a detached head state
 func (b *Branch) IsRealBranch() bool {
 	return b.AheadForPull != "" && b.BehindForPull != ""

pkg/gui/controllers/sync_controller.go

@@ -90,7 +90,7 @@ func (self *SyncController) push(currentBranch *models.Branch) error {
 	// if we are behind our upstream branch we'll ask if the user wants to force push
 	if currentBranch.IsTrackingRemote() {
 		opts := pushOpts{}
-		if currentBranch.IsBehindForPull() {
+		if currentBranch.IsBehindForPush() {
 			return self.requestToForcePush(currentBranch, opts)
 		} else {
 			return self.pushAux(currentBranch, opts)

pkg/integration/tests/sync/force_push_triangular.go

@@ -36,12 +36,6 @@ var ForcePushTriangular = NewIntegrationTest(NewIntegrationTestArgs{
 
 		t.Views().Files().IsFocused().Press(keys.Universal.Push)
 
-		// This results in an attempt to push normally, which fails with an error:
-		t.ExpectPopup().Alert().
-			Title(Equals("Error")).
-			Content(Contains("Updates were rejected. Please fetch and examine the remote changes before pushing again."))
-
-		/* EXPECTED:
 		t.ExpectPopup().Confirmation().
 			Title(Equals("Force push")).
 			Content(Equals("Your branch has diverged from the remote branch. Press <esc> to cancel, or <enter> to force push.")).
@@ -67,6 +61,5 @@ var ForcePushTriangular = NewIntegrationTest(NewIntegrationTestArgs{
 
 		t.Views().SubCommits().IsFocused().
 			Lines(Contains("one"))
-		*/
 	},
 })