feat: Make Custom{Build,Start}Command configurable in zbpack.toml

Linear: ZEA-1924

pkg/zeaburpack/plan.go

@@ -47,6 +47,34 @@ func Plan(opt PlanOptions) (types.PlanType, types.PlanMeta) {
 		src = afero.NewBasePathFs(afero.NewOsFs(), *opt.Path)
 	}
 
+	config := plan.NewProjectConfigurationFromFs(src)
+
+	// You can specify customBuildCommand, customStartCommand, and
+	// outputDir in the project configuration file, with the following
+	// form:
+	//
+	//     [project]
+	//     build_command = "..."
+	//     start_command = "..."
+	//     output_dir = "..."
+	//
+	//     [project.submodule]
+	//     build_command = "..."
+	//     start_command = "..."
+	//     output_dir = "..."
+	//
+	// The submodule-specific configuration overrides the project
+	// configuration if defined.
+	if opt.CustomBuildCommand == nil {
+		opt.CustomBuildCommand = getProjectConfigValue(config, *opt.SubmoduleName, "build_command")
+	}
+	if opt.CustomStartCommand == nil {
+		opt.CustomStartCommand = getProjectConfigValue(config, *opt.SubmoduleName, "start_command")
+	}
+	if opt.OutputDir == nil {
+		opt.OutputDir = getProjectConfigValue(config, *opt.SubmoduleName, "output_dir")
+	}
+
 	planner := plan.NewPlanner(
 		&plan.NewPlannerOptions{
 			Source:             src,
@@ -62,3 +90,31 @@ func Plan(opt PlanOptions) (types.PlanType, types.PlanMeta) {
 	t, m := planner.Plan()
 	return t, m
 }
+
+// getProjectConfigValue returns the project-specific configuration of the specified key.
+//
+// The format of project-specific configuration is like:
+//
+//	    [project]            # global
+//	    key = "value"
+//
+//		   [project.submodule]  # submoduleName specific
+//	    key = "value"        # overrides global
+//
+// If no such key is found in config, it returns nil.
+func getProjectConfigValue(config plan.ProjectConfiguration, submoduleName string, key string) *string {
+	submoduleKey := "project." + submoduleName + "."
+	globalKey := "project."
+
+	if config.IsSet(submoduleKey + key) {
+		value := config.GetString(submoduleKey + key)
+		return &value
+	}
+
+	if config.IsSet(globalKey + key) {
+		value := config.GetString(globalKey + key)
+		return &value
+	}
+
+	return nil
+}