Factor out CommitLoader.mainBranches into its own class, and store it in Model

pkg/commands/git_commands/existing_main_branches.go

@@ -0,0 +1,101 @@
+package git_commands
+
+import (
+	"strings"
+	"sync"
+
+	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
+	"github.com/jesseduffield/lazygit/pkg/utils"
+	"github.com/samber/lo"
+	"github.com/sasha-s/go-deadlock"
+)
+
+type ExistingMainBranches struct {
+	configuredMainBranches []string
+	existingBranches       []string
+
+	cmd   oscommands.ICmdObjBuilder
+	mutex *deadlock.Mutex
+}
+
+func NewExistingMainBranches(
+	configuredMainBranches []string,
+	cmd oscommands.ICmdObjBuilder,
+) *ExistingMainBranches {
+	return &ExistingMainBranches{
+		configuredMainBranches: configuredMainBranches,
+		existingBranches:       nil,
+		cmd:                    cmd,
+		mutex:                  &deadlock.Mutex{},
+	}
+}
+
+func (self *ExistingMainBranches) Get() []string {
+	self.mutex.Lock()
+	defer self.mutex.Unlock()
+
+	if self.existingBranches == nil {
+		self.existingBranches = self.determineMainBranches()
+	}
+
+	return self.existingBranches
+}
+
+func (self *ExistingMainBranches) Clear() {
+	self.mutex.Lock()
+	defer self.mutex.Unlock()
+
+	self.existingBranches = nil
+}
+
+func (self *ExistingMainBranches) determineMainBranches() []string {
+	var existingBranches []string
+	var wg sync.WaitGroup
+
+	existingBranches = make([]string, len(self.configuredMainBranches))
+
+	for i, branchName := range self.configuredMainBranches {
+		wg.Add(1)
+		i := i
+		branchName := branchName
+		go utils.Safe(func() {
+			defer wg.Done()
+
+			// Try to determine upstream of local main branch
+			if ref, err := self.cmd.New(
+				NewGitCmd("rev-parse").Arg("--symbolic-full-name", branchName+"@{u}").ToArgv(),
+			).DontLog().RunWithOutput(); err == nil {
+				existingBranches[i] = strings.TrimSpace(ref)
+				return
+			}
+
+			// If this failed, a local branch for this main branch doesn't exist or it
+			// has no upstream configured. Try looking for one in the "origin" remote.
+			ref := "refs/remotes/origin/" + branchName
+			if err := self.cmd.New(
+				NewGitCmd("rev-parse").Arg("--verify", "--quiet", ref).ToArgv(),
+			).DontLog().Run(); err == nil {
+				existingBranches[i] = ref
+				return
+			}
+
+			// If this failed as well, try if we have the main branch as a local
+			// branch. This covers the case where somebody is using git locally
+			// for something, but never pushing anywhere.
+			ref = "refs/heads/" + branchName
+			if err := self.cmd.New(
+				NewGitCmd("rev-parse").Arg("--verify", "--quiet", ref).ToArgv(),
+			).DontLog().Run(); err == nil {
+				existingBranches[i] = ref
+			}
+		})
+	}
+
+	wg.Wait()
+
+	existingBranches = lo.Filter(existingBranches, func(branch string, _ int) bool {
+		return branch != ""
+	})
+
+	return existingBranches
+}