From 89fd5f984cb153422b9e301689595f65adcd7ab4 Mon Sep 17 00:00:00 2001
From: Kent Rancourt <kent.rancourt@gmail.com>
Date: Mon, 25 Mar 2024 11:53:37 -0400
Subject: [PATCH] improve how new branches are created (#266)

Signed-off-by: Kent Rancourt <kent.rancourt@gmail.com>
---
 branches.go                                   | 13 ++++++-----
 docs/docs/30-how-to-guides/30-docker-image.md |  2 +-
 pkg/git/git.go                                | 19 +++++++++++----
 service.go                                    | 23 ++++++++++++++-----
 4 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/branches.go b/branches.go
index 303260c..407a54b 100644
--- a/branches.go
+++ b/branches.go
@@ -9,6 +9,7 @@ import (
 	"github.com/ghodss/yaml"
 
 	"github.com/akuity/kargo-render/internal/file"
+	"github.com/akuity/kargo-render/pkg/git"
 )
 
 // branchMetadata encapsulates details about an environment-specific branch for
@@ -104,12 +105,12 @@ func switchToTargetBranch(rc requestContext) error {
 		return fmt.Errorf("error creating new target branch: %w", err)
 	}
 	logger.Debug("created target branch")
-	if err =
-		writeBranchMetadata(branchMetadata{}, rc.repo.WorkingDir()); err != nil {
-		return fmt.Errorf("error writing blank target branch metadata: %w", err)
-	}
-	logger.Debug("wrote blank target branch metadata")
-	if err = rc.repo.AddAllAndCommit("Initial commit"); err != nil {
+	if err = rc.repo.Commit(
+		"Initial commit",
+		&git.CommitOptions{
+			AllowEmpty: true,
+		},
+	); err != nil {
 		return fmt.Errorf("error making initial commit to new target branch: %w", err)
 	}
 	logger.Debug("made initial commit to new target branch")
diff --git a/docs/docs/30-how-to-guides/30-docker-image.md b/docs/docs/30-how-to-guides/30-docker-image.md
index f735f76..f886cad 100644
--- a/docs/docs/30-how-to-guides/30-docker-image.md
+++ b/docs/docs/30-how-to-guides/30-docker-image.md
@@ -17,7 +17,7 @@ easiest option for experimenting locally with Kargo Render!
 Example usage:
 
 ```shell
-docker run -it ghcr.io/akuity/kargo-render:v0.1.0-rc.36 \
+docker run -it ghcr.io/akuity/kargo-render:v0.1.0-rc.37 \
   --repo https://github.com/<your GitHub handle>/kargo-render-demo-deploy \
   --repo-username <your GitHub handle> \
   --repo-password <a GitHub personal access token> \
diff --git a/pkg/git/git.go b/pkg/git/git.go
index fb963ab..dab504f 100644
--- a/pkg/git/git.go
+++ b/pkg/git/git.go
@@ -47,7 +47,7 @@ type Repo interface {
 	// Checkout checks out the specified branch.
 	Checkout(branch string) error
 	// Commit commits staged changes to the current branch.
-	Commit(message string) error
+	Commit(message string, opts *CommitOptions) error
 	// CreateChildBranch creates a new branch that is a child of the current
 	// branch.
 	CreateChildBranch(branch string) error
@@ -216,7 +216,7 @@ func (r *repo) AddAllAndCommit(message string) error {
 	if err := r.AddAll(); err != nil {
 		return err
 	}
-	return r.Commit(message)
+	return r.Commit(message, nil)
 }
 
 func (r *repo) Clean() error {
@@ -266,8 +266,19 @@ func (r *repo) Checkout(branch string) error {
 	return nil
 }
 
-func (r *repo) Commit(message string) error {
-	if _, err := libExec.Exec(r.buildCommand("commit", "-m", message)); err != nil {
+type CommitOptions struct {
+	AllowEmpty bool
+}
+
+func (r *repo) Commit(message string, opts *CommitOptions) error {
+	if opts == nil {
+		opts = &CommitOptions{}
+	}
+	cmdTokens := []string{"commit", "-m", message}
+	if opts.AllowEmpty {
+		cmdTokens = append(cmdTokens, "--allow-empty")
+	}
+	if _, err := libExec.Exec(r.buildCommand(cmdTokens...)); err != nil {
 		return fmt.Errorf(
 			"error committing changes to branch %q: %w",
 			r.currentBranch,
diff --git a/service.go b/service.go
index 74676b5..c491dd8 100644
--- a/service.go
+++ b/service.go
@@ -206,13 +206,24 @@ func (s *service) RenderManifests(
 		return res, fmt.Errorf("error loading branch metadata: %w", err)
 	}
 	if oldTargetBranchMetadata == nil {
-		return res, fmt.Errorf(
-			"target branch %q already exists, but does not appear to be managed by "+
-				"Kargo Render; refusing to overwrite branch contents",
-			rc.request.TargetBranch,
-		)
+		// The target branch doesn't appear to already be managed by Kargo Render.
+		// We'll let this slide if the branch is 100% empty, but we'll refuse to
+		// proceed otherwise.
+		var fileInfos []os.DirEntry
+		if fileInfos, err = os.ReadDir(rc.repo.WorkingDir()); err != nil {
+			return res, fmt.Errorf("error reading directory contents: %w", err)
+		}
+		if len(fileInfos) != 1 && fileInfos[0].Name() != ".git" {
+			return res, fmt.Errorf(
+				"target branch %q already exists, but does not appear to be managed by "+
+					"Kargo Render; refusing to overwrite branch contents",
+				rc.request.TargetBranch,
+			)
+		}
+		rc.target.oldBranchMetadata = branchMetadata{}
+	} else {
+		rc.target.oldBranchMetadata = *oldTargetBranchMetadata
 	}
-	rc.target.oldBranchMetadata = *oldTargetBranchMetadata
 
 	if rc.target.commit.branch, err = switchToCommitBranch(rc); err != nil {
 		return res, fmt.Errorf("error switching to commit branch: %w", err)