feat(xatu): report empty let expressions

src/xatu/ast.rs

@@ -29,6 +29,7 @@ impl std::fmt::Display for SourceRange {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum NodeData {
     Apply(Apply),
+    LetIn(LetIn),
     Inherit(Inherit),
 }
 
@@ -54,6 +55,11 @@ pub struct Select {
     pub attrs: Vec<Ident>,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct LetIn {
+    pub binding_count: usize,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Inherit {
     pub attr_count: usize,