Expose the template ast

Sometimes a consumer of a template needs to know what objects were used.
In my case, a template can reference secret values from a secret store
vault and instead of passing all possible secrets to the template only
to render two of them, we use the ast to determine which are used and
only retrieve those values from the vault before rendering the template.

Exposing the ast allows us to use the liquid APIs just like normal,
without having to jump through hoops to build the ast ourselves using
the other types exported in this library.

Signed-off-by: Carolyn Van Slyck <[email protected]>

template.go

@@ -24,6 +24,12 @@ func newTemplate(cfg *render.Config, source []byte, path string, line int) (*Tem
 	return &Template{root, cfg}, nil
 }
 
+// GetRoot returns the root node of the abstract syntax tree (AST) representing
+// the parsed template.
+func (t *Template) GetRoot() render.Node {
+	return t.root
+}
+
 // Render executes the template with the specified variable bindings.
 func (t *Template) Render(vars Bindings) ([]byte, SourceError) {
 	buf := new(bytes.Buffer)

template_test.go

@@ -9,6 +9,12 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestTemplate_GetRoot(t *testing.T) {
+	root := &render.SeqNode{}
+	tmpl := Template{root: root}
+	require.Same(t, root, tmpl.GetRoot())
+}
+
 func TestTemplate_RenderString(t *testing.T) {
 	engine := NewEngine()
 	tpl, err := engine.ParseTemplate([]byte(`{{ "hello world" | capitalize }}`))