Pipeline: Add 'tpl' template function

Signed-off-by: Richard Kosegi <richard.kosegi@gmail.com>

pipeline/template_engine.go

@@ -27,8 +27,25 @@ type templateEngine struct {
 	fm template.FuncMap
 }
 
+func tplFunc(tmpl *template.Template) func(string, interface{}) (string, error) {
+	return func(tpl string, data interface{}) (string, error) {
+		t, _ := tmpl.Clone()
+		t, err := tmpl.New(tmpl.Name()).Parse(tpl)
+		if err != nil {
+			return "", err
+		}
+		var buf strings.Builder
+		err = t.Execute(&buf, data)
+		return buf.String(), err
+	}
+}
+
 func renderTemplate(tmplStr string, data interface{}, fm template.FuncMap) (string, error) {
 	tmpl := template.New("tmpl").Funcs(fm)
+	tmpl.Funcs(template.FuncMap{
+		"tpl": tplFunc(tmpl),
+	})
+	tplFunc(tmpl)
 	_, err := tmpl.Parse(tmplStr)
 	if err != nil {
 		return "", err

pipeline/template_engine_test.go

@@ -61,3 +61,26 @@ func TestRenderTemplate(t *testing.T) {
 	_, err = renderTemplate("{{ .a }}", "", sprig.TxtFuncMap())
 	assert.Error(t, err)
 }
+
+func TestTemplateEngineRenderTpl(t *testing.T) {
+	var (
+		out string
+		err error
+	)
+	out, err = renderTemplate("{{ tpl .T . }}", map[string]interface{}{
+		"T": "{{ add .X 3 }}",
+		"X": 10,
+	}, sprig.TxtFuncMap())
+	assert.NoError(t, err)
+	assert.Equal(t, "13", out)
+}
+
+func TestTemplateEngineRenderTplInvalid(t *testing.T) {
+	var (
+		err error
+	)
+	_, err = renderTemplate("{{ tpl .T . }}", map[string]interface{}{
+		"T": "{{",
+	}, sprig.TxtFuncMap())
+	assert.Error(t, err)
+}