Detect buildpacks for specific branch (fall back to deploy-branch to be consistent with deployment behavior)

plugins/buildpacks/functions.go

@@ -64,15 +64,25 @@ func validBuildpackURL(buildpack string) (string, error) {
 	return buildpack, fmt.Errorf("Invalid buildpack specified: %v", buildpack)
 }
 
-func checkoutBareGitRepo(sourceWorkDir string) (string, error) {
+func checkoutBareGitRepo(sourceWorkDir string, branch string) (string, error) {
 	tmpdir, err := os.MkdirTemp("", "bare-git-checkout")
 	if err != nil {
 		return "", fmt.Errorf("Unable to create temporary directory: %s", err.Error())
 	}
 
+	args := []string{
+		"--git-dir=" + sourceWorkDir,
+		"--work-tree=" + tmpdir,
+		"checkout", "-f",
+	}
+
+	if branch != "" {
+		args = append(args, branch)
+	}
+
 	result, err := common.CallExecCommand(common.ExecCommandInput{
 		Command: "git",
-		Args:    []string{"--git-dir=" + sourceWorkDir, "--work-tree=" + tmpdir, "checkout", "-f"},
+		Args:    args,
 	})
 
 	if err != nil {

plugins/buildpacks/src/commands/commands.go

@@ -20,7 +20,7 @@ Additional commands:`
 	helpContent = `
     buildpacks:add [--index 1] <app> <buildpack>, Add new app buildpack while inserting into list of buildpacks if necessary
     buildpacks:clear <app>, Clear all buildpacks set on the app
-    buildpacks:detect <app>, Detect the buildpack for an app
+    buildpacks:detect <app> [--branch <branch-name>], Detect the buildpack for an app (if not specified, the branch flag defaults to the deploy branch)
     buildpacks:list <app>, List all buildpacks for an app
     buildpacks:remove <app> <buildpack>, Remove a buildpack set on the app
     buildpacks:report [<app>] [<flag>], Displays a buildpack report for one or more apps

plugins/buildpacks/src/subcommands/subcommands.go

@@ -32,9 +32,13 @@ func main() {
 		err = buildpacks.CommandClear(appName)
 	case "detect":
 		args := flag.NewFlagSet("buildpacks:detect", flag.ExitOnError)
+		branch := args.String("branch", "", "--branch: the branch to detect against (defaults to the deploy branch)")
 		args.Parse(os.Args[2:])
 		appName := args.Arg(0)
-		err = buildpacks.CommandDetect(appName)
+		if *branch == "" {
+            *branch = common.PropertyGet("git", appName, "deploy-branch")
+		}
+		err = buildpacks.CommandDetect(appName, *branch)
 	case "list":
 		args := flag.NewFlagSet("buildpacks:list", flag.ExitOnError)
 		args.Parse(os.Args[2:])

plugins/buildpacks/subcommands.go

@@ -32,13 +32,13 @@ func CommandClear(appName string) error {
 }
 
 // CommandDetect implements buildpacks:detect
-func CommandDetect(appName string) error {
+func CommandDetect(appName string, branch string) (err error) {
 	if err := common.VerifyAppName(appName); err != nil {
 		return err
 	}
 
 	workDir := common.AppRoot(appName)
-	checkedOutDir, err := checkoutBareGitRepo(workDir)
+	checkedOutDir, err := checkoutBareGitRepo(workDir, branch)
     if err != nil {
         return err
     }