lua: skip top-level guard when chunk has no top-level return; loadstring sees user globals

lib/lua/transpile.sx

@@ -568,12 +568,39 @@
                   (else sx)))))))
       (else sx))))
 
+(define
+  lua-has-top-return?
+  (fn (node)
+    (cond
+      ((not (= (type-of node) "list")) false)
+      ((= (len node) 0) false)
+      ((= (first node) (quote lua-return)) true)
+      ((or (= (first node) (quote lua-function))
+           (= (first node) (quote lua-local-function))
+           (= (first node) (quote lua-function-decl)))
+        false)
+      (else
+        (lua-has-top-return-children? (rest node) 0)))))
+
+(define
+  lua-has-top-return-children?
+  (fn (children i)
+    (cond
+      ((>= i (len children)) false)
+      ((lua-has-top-return? (nth children i)) true)
+      (else (lua-has-top-return-children? children (+ i 1))))))
+
 (define
   lua-eval-ast
   (fn (src)
-    (let ((sx (lua-transpile src)))
-      (let ((sx2 (lua-unwrap-final-return sx)))
-        (eval-expr (lua-tx-function-guard sx2))))))
+    (let ((parsed (lua-parse src)))
+      (let ((sx (lua-tx parsed)))
+        (let ((sx2 (lua-unwrap-final-return sx)))
+          (cond
+            ((lua-has-top-return? parsed)
+              (eval-expr (lua-tx-function-guard sx2)))
+            (else
+              (eval-expr sx2))))))))
 
 (define
   lua-tx-multi-args