Desugar from the outside in

src/ast/basic.rs

@@ -37,6 +37,17 @@ impl Space {
             span,
         }
     }
+
+    pub fn then(mut self, other: Self) -> Self {
+        self.lines.extend(other.lines);
+        self.span = self.span.join(other.span);
+        self
+    }
+
+    pub fn then_line(mut self, line: Line) -> Self {
+        self.lines.push(line);
+        self
+    }
 }
 
 #[derive(Clone)]