simplify the custom template code

libs/template/resolver.go

@@ -47,6 +47,10 @@ type Resolver struct {
 	Branch string
 }
 
+// ErrCustomSelected is returned when the user selects the "custom..." option
+// in the prompt UI when they run `databricks bundle init`. This error signals
+// the upstream callsite to show documentation to the user on how to use a custom
+// template.
 var ErrCustomSelected = errors.New("custom template selected")
 
 // Configures the reader and the writer for template and returns
@@ -83,12 +87,25 @@ func (r Resolver) Resolve(ctx context.Context) (*Template, error) {
 		return nil, ErrCustomSelected
 	}
 
-	tmpl := Get(templateName)
+	tmpl := GetDatabricksTemplate(templateName)
 
-	// If the user directory provided a template path or URL that is not a built-in template,
-	// then configure a reader for the template.
+	// If we could not find a databricks template with the name provided by the user,
+	// then we assume that the user provided us with a reference to a custom template.
+	//
+	// This reference could be one of:
+	// 1. Path to a local template directory.
+	// 2. URL to a Git repository containing a template.
+	//
+	// We resolve the appropriate reader according to the reference provided by the user.
 	if tmpl == nil {
-		tmpl = Get(Custom)
+		tmpl = &Template{
+			name: Custom,
+			// We use a writer that does not log verbose telemetry for custom templates.
+			// This is important because template definitions can contain PII that we
+			// do not want to centralize.
+			Writer: &defaultWriter{},
+		}
+
 		if isRepoUrl(r.TemplatePathOrUrl) {
 			tmpl.Reader = &gitReader{
 				gitUrl:      r.TemplatePathOrUrl,
@@ -101,9 +118,7 @@ func (r Resolver) Resolve(ctx context.Context) (*Template, error) {
 				path: r.TemplatePathOrUrl,
 			}
 		}
-
 	}
-
 	err = tmpl.Writer.Configure(ctx, r.ConfigFile, r.OutputDir)
 	if err != nil {
 		return nil, err

libs/template/template.go

@@ -29,14 +29,10 @@ const (
 	DbtSql        TemplateName = "dbt-sql"
 	MlopsStacks   TemplateName = "mlops-stacks"
 	DefaultPydabs TemplateName = "default-pydabs"
-
-	// Custom represents any template that is not one of the above default
-	// templates. It's a catch all for any custom templates that customers provide
-	// as a path or URL argument.
-	Custom TemplateName = "custom..."
+	Custom        TemplateName = "custom"
 )
 
-var allTemplates = []Template{
+var databricksTemplates = []Template{
 	{
 		name:        DefaultPython,
 		description: "The default Python template for Notebooks / Delta Live Tables / Workflows",
@@ -69,28 +65,23 @@ var allTemplates = []Template{
 		Reader:      &gitReader{gitUrl: "https://databricks.github.io/workflows-authoring-toolkit/pydabs-template.git", cloneFunc: git.Clone},
 		Writer:      &writerWithFullTelemetry{},
 	},
-	{
-		name:        Custom,
-		description: "Bring your own template",
-		// Reader is determined at runtime based on the user input.
-		Reader: nil,
-		Writer: &defaultWriter{},
-	},
 }
 
 func HelpDescriptions() string {
 	var lines []string
-	for _, template := range allTemplates {
+	for _, template := range databricksTemplates {
 		if template.name != Custom && !template.hidden {
 			lines = append(lines, fmt.Sprintf("- %s: %s", template.name, template.description))
 		}
 	}
 	return strings.Join(lines, "\n")
 }
 
+var customTemplateDescription = "Bring your own template"
+
 func options() []cmdio.Tuple {
-	names := make([]cmdio.Tuple, 0, len(allTemplates))
-	for _, template := range allTemplates {
+	names := make([]cmdio.Tuple, 0, len(databricksTemplates))
+	for _, template := range databricksTemplates {
 		if template.hidden {
 			continue
 		}
@@ -100,6 +91,11 @@ func options() []cmdio.Tuple {
 		}
 		names = append(names, tuple)
 	}
+
+	names = append(names, cmdio.Tuple{
+		Name: "custom...",
+		Id:   customTemplateDescription,
+	})
 	return names
 }
 
@@ -112,7 +108,11 @@ func SelectTemplate(ctx context.Context) (TemplateName, error) {
 		return "", err
 	}
 
-	for _, template := range allTemplates {
+	if description == customTemplateDescription {
+		return TemplateName(""), ErrCustomSelected
+	}
+
+	for _, template := range databricksTemplates {
 		if template.description == description {
 			return template.name, nil
 		}
@@ -121,8 +121,8 @@ func SelectTemplate(ctx context.Context) (TemplateName, error) {
 	panic("this should never happen - template not found")
 }
 
-func Get(name TemplateName) *Template {
-	for _, template := range allTemplates {
+func GetDatabricksTemplate(name TemplateName) *Template {
+	for _, template := range databricksTemplates {
 		if template.name == name || slices.Contains(template.aliases, string(name)) {
 			return &template
 		}

libs/template/template_test.go

@@ -39,7 +39,7 @@ func TestBundleInitRepoName(t *testing.T) {
 }
 
 func TestTemplateTelemetryIsCapturedForAllDefaultTemplates(t *testing.T) {
-	for _, tmpl := range allTemplates {
+	for _, tmpl := range databricksTemplates {
 		w := tmpl.Writer
 
 		if tmpl.name == Custom {
@@ -64,7 +64,7 @@ func TestTemplateGet(t *testing.T) {
 	}
 
 	for _, name := range names {
-		tmpl := Get(name)
+		tmpl := GetDatabricksTemplate(name)
 		assert.Equal(t, tmpl.name, name)
 	}
 
@@ -75,10 +75,10 @@ func TestTemplateGet(t *testing.T) {
 	}
 
 	for _, name := range notExist {
-		tmpl := Get(TemplateName(name))
+		tmpl := GetDatabricksTemplate(TemplateName(name))
 		assert.Nil(t, tmpl)
 	}
 
 	// Assert the alias works.
-	assert.Equal(t, MlopsStacks, Get(TemplateName("mlops-stack")).name)
+	assert.Equal(t, MlopsStacks, GetDatabricksTemplate(TemplateName("mlops-stack")).name)
 }

libs/template/writer.go

@@ -21,7 +21,13 @@ const (
 )
 
 type Writer interface {
+	// Configure the writer with:
+	// 1. The path to the config file (if any) that contains input values for the
+	// template.
+	// 2. The output directory where the template will be materialized.
 	Configure(ctx context.Context, configPath, outputDir string) error
+
+	// Materialize the template to the local file system.
 	Materialize(ctx context.Context, r Reader) error
 }