feat: [MER-1493] show up to date info about branches in stack tree (#96)

add the following info about each branch for `av stack tree` (will probably need some UI improvements)
- is it up to date with parent branch
- is it up to date with upstream/remote branch
- if PR link if it exists

<img width="619" alt="Screen Shot 2023-05-01 at 2 12 32 PM" src="https://user-images.githubusercontent.com/13113118/235532267-3ffbcad9-2e67-4f53-a6df-cc38bae4173f.png">

cmd/av/stack_tree.go

@@ -71,14 +71,87 @@ func printStackTree(repo *git.Repo, branches map[string]meta.Branch, currentBran
 		fmt.Printf("%s<ERROR: unknown branch: %s>\n", indent, root)
 		return
 	}
+
+	branchInfo, err := getBranchInfo(repo, branch)
+	if err != nil {
+		fmt.Printf("<ERROR: cannot get branch info: %v>\n", err)
+		return
+	}
+
 	if currentBranch == branch.Name {
 		_, _ = fmt.Print(
-			indent, colors.Success("* "), colors.Success(branch.Name), "\n",
+			indent, colors.Success("* "), colors.Success(branch.Name), " ", colors.Faint(branchInfo), "\n",
 		)
 	} else {
-		_, _ = fmt.Printf("%s%s\n", indent, branch.Name)
+		_, _ = fmt.Print(indent, branch.Name, " ", colors.Faint(branchInfo), "\n")
 	}
 	for _, next := range branch.Children {
 		printStackTree(repo, branches, currentBranch, next, depth+1)
 	}
 }
+
+func getBranchInfo(repo *git.Repo, branch meta.Branch) (string, error) {
+	var branchInfo string
+
+	parentStatus, err := getParentStatus(repo, branch)
+	if err != nil {
+		return "", err
+	}
+
+	upstreamStatus, err := getUpstreamStatus(repo, branch)
+	if err != nil {
+		return "", err
+	}
+
+	branchStatus := strings.Trim(fmt.Sprintf("%s, %s", parentStatus, upstreamStatus), ", ")
+	if branchStatus != "" {
+		branchInfo = fmt.Sprintf("(%s)", branchStatus)
+	}
+
+	if branch.PullRequest != nil && branch.PullRequest.Permalink != "" {
+		branchInfo = branch.PullRequest.Permalink + " " + branchInfo
+	}
+
+	return branchInfo, nil
+}
+
+// Check if branch is up to date with the parent branch.
+func getParentStatus(repo *git.Repo, branch meta.Branch) (string, error) {
+	parentHead, err := repo.RevParse(&git.RevParse{Rev: branch.Parent.Name})
+	if err != nil {
+		return "", err
+	}
+
+	mergeBase, err := repo.MergeBase(&git.MergeBase{
+		Revs: []string{parentHead, branch.Name},
+	})
+	if err != nil {
+		return "", err
+	}
+	if mergeBase == parentHead {
+		return "", nil
+	}
+
+	return "needs sync", nil
+}
+
+// Check if branch is up to date with the upstream branch.
+// This is doing `git diff <givenBranch> remotes/origin/<givenBranch>`
+func getUpstreamStatus(repo *git.Repo, branch meta.Branch) (string, error) {
+	upstreamExists, err := repo.DoesRemoteBranchExist(branch.Name)
+	if err != nil || !upstreamExists {
+		return "not pushed", nil
+	}
+
+	upstreamBranch := fmt.Sprintf("remotes/origin/%s", branch.Name)
+	upstreamDiff, err := repo.Diff(&git.DiffOpts{Quiet: true, Branch1: branch.Name, Branch2: upstreamBranch})
+	if err != nil {
+		return "", err
+	} 
+
+	if upstreamDiff.Empty {
+		return "", nil
+	}
+
+	return "not pushed", nil
+}

internal/git/diff.go

@@ -16,6 +16,10 @@ type DiffOpts struct {
 	Quiet bool
 	// If true, shows the colored diff.
 	Color bool
+	// Both branches need to be specified in order to find the diff between the two branches.
+	// If a Commit is specified, the branches will not be used.
+	Branch1 string
+	Branch2 string
 }
 
 type Diff struct {
@@ -31,7 +35,11 @@ func (r *Repo) Diff(d *DiffOpts) (*Diff, error) {
 	}
 	if d.Commit != "" {
 		args = append(args, d.Commit)
+	} else if d.Branch1 != "" && d.Branch2 != "" {
+		args = append(args, d.Branch1)
+		args = append(args, d.Branch2)
 	}
+
 	if d.Color {
 		args = append(args, "--color=always")
 	}

internal/git/git.go

@@ -2,6 +2,7 @@ package git
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"net/url"
 	"os"
@@ -192,6 +193,21 @@ func (r *Repo) HasChangesToBeCommitted() (bool, error) {
 	return out.ExitCode == 1, nil
 }
 
+func (r *Repo) DoesRemoteBranchExist(branch string) (bool, error) {
+	remoteBranch := fmt.Sprintf("refs/remotes/origin/%s", branch)
+	out, err := r.Run(&RunOpts{
+		Args: []string{"show-ref", remoteBranch},
+	})
+	if err != nil {
+		return false, errors.Errorf("remote branch does not exist: %v", err)
+	}
+
+	if len(out.Stdout) > 0 {
+		return true, nil
+	}
+	return false, nil
+}
+
 type CheckoutBranch struct {
 	// The name of the branch to checkout.
 	Name string