feat: make pr-based promotions work with kargo render

Dockerfile

@@ -68,7 +68,7 @@ RUN GRPC_HEALTH_PROBE_VERSION=v0.4.15 && \
 # - supports development
 # - not used for official image builds
 ####################################################################################################
-FROM ghcr.io/akuity/kargo-render:v0.1.0-rc.35 as back-end-dev
+FROM ghcr.io/akuity/kargo-render:v0.1.0-rc.38 as back-end-dev
 
 USER root
 
@@ -103,7 +103,7 @@ CMD ["pnpm", "dev"]
 # - the official image we publish
 # - purposefully last so that it is the default target when building
 ####################################################################################################
-FROM ghcr.io/akuity/kargo-render:v0.1.0-rc.35 as final
+FROM ghcr.io/akuity/kargo-render:v0.1.0-rc.38 as final
 
 USER root
 

internal/controller/git/git.go

@@ -30,6 +30,12 @@
 	Password string `json:"password,omitempty"`
 }
 
+// CommitOptions represents options for committing changes to a git repository.
+type CommitOptions struct {
+	// AllowEmpty indicates whether an empty commit should be allowed.
+	AllowEmpty bool
+}
+
 // Repo is an interface for interacting with a git repository.
 type Repo interface {
 	// AddAll stages pending changes for commit.
@@ -46,7 +52,7 @@
 	// 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
@@ -135,7 +141,7 @@
 	repoCreds RepoCredentials,
 	opts *CloneOptions,
 ) (Repo, error) {
-	homeDir, err := os.MkdirTemp("", "")
+	homeDir, err := os.MkdirTemp("", "repo-")
 	if err != nil {
 		return nil, fmt.Errorf("error creating home directory for repo %q: %w", repoURL, err)
 	}
@@ -162,7 +168,7 @@
 	if err := r.AddAll(); err != nil {
 		return err
 	}
-	return r.Commit(message)
+	return r.Commit(message, nil)
 }
 
 func (r *repo) Clean() error {
@@ -226,8 +232,16 @@
 	return nil
 }
 
-func (r *repo) Commit(message string) error {
-	if _, err := libExec.Exec(r.buildCommand("commit", "-m", message)); err != nil {
+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, err)
 	}
 	return nil

internal/controller/promotion/git.go

@@ -13,6 +13,8 @@
 	"github.com/akuity/kargo/internal/logging"
 )
 
+const tmpPrefix = "repo-scrap-"
+
 // gitMechanism is an implementation of the Mechanism interface that uses Git to
 // update configuration in a repository. It is easily configured to support
 // different types of configuration management tools.
@@ -45,6 +47,7 @@
 	applyConfigManagementFn func(
 		update kargoapi.GitRepoUpdate,
 		newFreight kargoapi.FreightReference,
+		sourceCommit string,
 		homeDir string,
 		workingDir string,
 	) ([]string, error)
@@ -61,6 +64,7 @@
 	applyConfigManagementFn func(
 		update kargoapi.GitRepoUpdate,
 		newFreight kargoapi.FreightReference,
+		sourceCommit string,
 		homeDir string,
 		workingDir string,
 	) ([]string, error),
@@ -294,11 +298,17 @@
 		}
 	}
 
+	sourceCommitID, err := repo.LastCommitID()
+	if err != nil {
+		return "", err // TODO: Wrap this
+	}
+
 	var changes []string
 	if g.applyConfigManagementFn != nil {
 		if changes, err = g.applyConfigManagementFn(
 			update,
 			newFreight,
+			sourceCommitID,
 			repo.HomeDir(),
 			repo.WorkingDir(),
 		); err != nil {
@@ -310,7 +320,7 @@
 	// Sometimes we don't write to the same branch we read from...
 	if readRef != writeBranch {
 		var tempDir string
-		tempDir, err = os.MkdirTemp("", "")
+		tempDir, err = os.MkdirTemp("", tmpPrefix)
 		if err != nil {
 			return "", fmt.Errorf("error creating temp directory for pending changes: %w", err)
 		}

internal/controller/promotion/git_test.go

@@ -24,7 +24,11 @@ func TestNewGitMechanism(t *testing.T) {
 		func([]kargoapi.GitRepoUpdate) []kargoapi.GitRepoUpdate {
 			return nil
 		},
-		func(kargoapi.GitRepoUpdate, kargoapi.FreightReference, string, string) ([]string, error) {
+		func(
+			kargoapi.GitRepoUpdate,
+			kargoapi.FreightReference,
+			string, string, string,
+		) ([]string, error) {
 			return nil, nil
 		},
 	)

internal/controller/promotion/helm.go

@@ -64,6 +64,7 @@ type helmer struct {
 func (h *helmer) apply(
 	update kargoapi.GitRepoUpdate,
 	newFreight kargoapi.FreightReference,
+	_ string, // TODO: sourceCommit would be a nice addition to the commit message
 	homeDir string,
 	workingDir string,
 ) ([]string, error) {

internal/controller/promotion/helm_test.go

@@ -254,6 +254,7 @@ func TestHelmerApply(t *testing.T) {
 				kargoapi.FreightReference{}, // The way the tests are structured, this value doesn't matter
 				"",
 				"",
+				"",
 			)
 			testCase.assertions(t, changes, err)
 		})

internal/controller/promotion/kustomize.go

@@ -47,6 +47,7 @@ type kustomizer struct {
 func (k *kustomizer) apply(
 	update kargoapi.GitRepoUpdate,
 	newFreight kargoapi.FreightReference,
+	_ string, // TODO: sourceCommit would be a nice addition to the commit message
 	_ string,
 	workingDir string,
 ) ([]string, error) {

internal/controller/promotion/kustomize_test.go

@@ -168,6 +168,7 @@ func TestKustomizerApply(t *testing.T) {
 				},
 				"",
 				"",
+				"",
 			)
 			testCase.assertions(t, changes, err)
 		})

internal/controller/promotion/pullrequest.go

@@ -20,7 +20,27 @@
 // we like (i.e. not a descendant of base), recreate it.
 func preparePullRequestBranch(repo git.Repo, prBranch string, base string) error {
 	origBranch := repo.CurrentBranch()
-	if err := repo.Checkout(base); err != nil {
+	baseBranchExists, err := repo.RemoteBranchExists(base)
+	if err != nil {
+		return err
+	}
+	if !baseBranchExists {
+		// Base branch doesn't exist. Create it!
+		if err = repo.CreateOrphanedBranch(base); err != nil {
+			return err
+		}
+		if err = repo.Commit(
+			"Initial commit",
+			&git.CommitOptions{
+				AllowEmpty: true,
+			},
+		); err != nil {
+			return err
+		}
+		if err = repo.Push(false); err != nil {
+			return err
+		}
+	} else if err = repo.Checkout(base); err != nil {
 		return err
 	}
 	prBranchExists, err := repo.RemoteBranchExists(prBranch)