Hide shell functions from _G using upvalues on the main chunk

Store __command, __interactive, __getenv, __setenv as upvalues
populated by lua_load() from the registry, keeping them invisible
to user code while accessible to the parser's codegen.

lapi.c

@@ -29,6 +29,7 @@
 #include "ltm.h"
 #include "lundump.h"
 #include "lvm.h"
+#include "lcmd.h"
 
 
 
@@ -1135,6 +1136,27 @@ LUA_API int lua_load (lua_State *L, lua_Reader reader, void *data,
       setobj(L, f->upvals[0]->v.p, &gt);
       luaC_barrier(L, f->upvals[0], &gt);
     }
+    if (f->nupvalues >= LUSH_NUM_UPVALS) {  /* has lush upvalues? */
+      /* populate shell function upvalues from registry */
+      Table *regt = hvalue(&G(L)->l_registry);
+      TValue lushtv;
+      lu_byte tag = luaH_getint(regt, LUA_RIDX_LUSH, &lushtv);
+      if (novariant(tag) == LUA_TTABLE) {
+        static const char *const fields[] = {
+          "command", "interactive", "getenv", "setenv"
+        };
+        Table *lusht = hvalue(&lushtv);
+        int i;
+        for (i = 0; i < 4; i++) {
+          TValue val;
+          TString *key = luaS_new(L, fields[i]);
+          if (luaH_getstr(lusht, key, &val) != LUA_TNIL) {
+            setobj(L, f->upvals[i + 1]->v.p, &val);
+            luaC_barrier(L, f->upvals[i + 1], &val);
+          }
+        }
+      }
+    }
   }
   lua_unlock(L);
   return APIstatus(status);