Fix checking out a different branch while pushing a branch for the first time (#4214)

- **PR Description**

When pushing a branch that didn't have an upstream yet, we use the
command line

  git push --set-upstream origin HEAD:branch-name

The HEAD: part of this is too unspecific; when checking out a different
branch while the push is still running, then git will set the upstream
branch on the newly checked out branch, not the branch that was being
pushed. This might be considered a bug in git; you might expect that it
resolves HEAD at the beginning of the operation, and uses the result at
the end.

But we can easily work around this by explicitly supplying the real
branch name instead of HEAD.

Fixes #4207.

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

* [x] Cheatsheets are up-to-date (run `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)
* [ ] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

pkg/commands/git_commands/sync.go

@@ -1,6 +1,8 @@
 package git_commands
 
 import (
+	"fmt"
+
 	"github.com/go-errors/errors"
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
@@ -20,6 +22,7 @@ func NewSyncCommands(gitCommon *GitCommon) *SyncCommands {
 type PushOpts struct {
 	Force          bool
 	ForceWithLease bool
+	CurrentBranch  string
 	UpstreamRemote string
 	UpstreamBranch string
 	SetUpstream    bool
@@ -35,7 +38,7 @@ func (self *SyncCommands) PushCmdObj(task gocui.Task, opts PushOpts) (oscommands
 		ArgIf(opts.ForceWithLease, "--force-with-lease").
 		ArgIf(opts.SetUpstream, "--set-upstream").
 		ArgIf(opts.UpstreamRemote != "", opts.UpstreamRemote).
-		ArgIf(opts.UpstreamBranch != "", "HEAD:"+opts.UpstreamBranch).
+		ArgIf(opts.UpstreamBranch != "", fmt.Sprintf("refs/heads/%s:%s", opts.CurrentBranch, opts.UpstreamBranch)).
 		ToArgv()
 
 	cmdObj := self.cmd.New(cmdArgs).PromptOnCredentialRequest(task)

pkg/commands/git_commands/sync_test.go

@@ -44,11 +44,12 @@ func TestSyncPush(t *testing.T) {
 			testName: "Push with force disabled, upstream supplied",
 			opts: PushOpts{
 				ForceWithLease: false,
+				CurrentBranch:  "master",
 				UpstreamRemote: "origin",
 				UpstreamBranch: "master",
 			},
 			test: func(cmdObj oscommands.ICmdObj, err error) {
-				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "origin", "HEAD:master"})
+				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "origin", "refs/heads/master:master"})
 				assert.NoError(t, err)
 			},
 		},
@@ -56,12 +57,13 @@ func TestSyncPush(t *testing.T) {
 			testName: "Push with force disabled, setting upstream",
 			opts: PushOpts{
 				ForceWithLease: false,
+				CurrentBranch:  "master-local",
 				UpstreamRemote: "origin",
 				UpstreamBranch: "master",
 				SetUpstream:    true,
 			},
 			test: func(cmdObj oscommands.ICmdObj, err error) {
-				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "--set-upstream", "origin", "HEAD:master"})
+				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "--set-upstream", "origin", "refs/heads/master-local:master"})
 				assert.NoError(t, err)
 			},
 		},
@@ -69,12 +71,13 @@ func TestSyncPush(t *testing.T) {
 			testName: "Push with force-with-lease enabled, setting upstream",
 			opts: PushOpts{
 				ForceWithLease: true,
+				CurrentBranch:  "master",
 				UpstreamRemote: "origin",
 				UpstreamBranch: "master",
 				SetUpstream:    true,
 			},
 			test: func(cmdObj oscommands.ICmdObj, err error) {
-				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "--force-with-lease", "--set-upstream", "origin", "HEAD:master"})
+				assert.Equal(t, cmdObj.Args(), []string{"git", "push", "--force-with-lease", "--set-upstream", "origin", "refs/heads/master:master"})
 				assert.NoError(t, err)
 			},
 		},

pkg/gui/controllers/sync_controller.go

@@ -200,6 +200,7 @@ func (self *SyncController) pushAux(currentBranch *models.Branch, opts pushOpts)
 			git_commands.PushOpts{
 				Force:          opts.force,
 				ForceWithLease: opts.forceWithLease,
+				CurrentBranch:  currentBranch.Name,
 				UpstreamRemote: opts.upstreamRemote,
 				UpstreamBranch: opts.upstreamBranch,
 				SetUpstream:    opts.setUpstream,