From 16a2eadb66c26677dade15ac0bdc9578e8742fa9 Mon Sep 17 00:00:00 2001
From: Julien Danjou <julien@danjou.info>
Date: Mon, 27 Oct 2008 14:17:12 +0100
Subject: [PATCH] wibox: check for table loops

Signed-off-by: Julien Danjou <julien@danjou.info>
---
 luaa.c  | 33 +++++++++++++++++++++++++++++++++
 luaa.h  |  1 +
 wibox.c |  2 ++
 3 files changed, 36 insertions(+)

diff --git a/luaa.c b/luaa.c
index 8da05ef3..e2e6d4c4 100644
--- a/luaa.c
+++ b/luaa.c
@@ -531,6 +531,39 @@ luaA_hasitem(lua_State *L, const void *item)
     return false;
 }
 
+/** Check if a table is a loop. When using table as direct acyclic digram,
+ * this is useful.
+ * \param L The Lua VM state.
+ * \param idx The index of the table in the stack
+ * \return True if the table loops.
+ */
+bool
+luaA_isloop(lua_State *L, int idx)
+{
+    if(lua_istable(L, idx))
+    {
+        lua_pushvalue(L, idx); /* push table on top */
+        if(luaA_hasitem(L, lua_topointer(L, -1)))
+        {
+            lua_pop(L, 1); /* remove pushed table */
+            return true;
+        }
+        lua_pushnil(L);
+        while(luaA_next(L, -2))
+        {
+            /* check for recursivity */
+            if(luaA_isloop(L, -1))
+            {
+                lua_pop(L, 2); /* remove key and value */
+                return true;
+            }
+            lua_pop(L, 1); /* remove value */
+        }
+        lua_pop(L, 1); /* remove pushed table */
+    }
+    return false;
+}
+
 /** Object table.
  * This table can use safely object as key.
  * \param L The Lua VM state.
diff --git a/luaa.h b/luaa.h
index 515cd89a..340dc5cb 100644
--- a/luaa.h
+++ b/luaa.h
@@ -345,6 +345,7 @@ int luaA_pushcolor(lua_State *, const xcolor_t *);
 bool luaA_hasitem(lua_State *, const void *);
 void luaA_table2wtable(lua_State *);
 int luaA_next(lua_State *, int);
+bool luaA_isloop(lua_State *, int);
 
 #define hooks_property(c, prop) \
     do { \
diff --git a/wibox.c b/wibox.c
index 402ac163..8c4d0604 100644
--- a/wibox.c
+++ b/wibox.c
@@ -972,6 +972,8 @@ luaA_wibox_newindex(lua_State *L)
             }
         break;
       case A_TK_WIDGETS:
+        if(luaA_isloop(L, 3))
+            luaL_error(L, "table is looping, cannot use this as widget table");
         luaA_register(L, 3, &(*wibox)->widgets_table);
         /* recompute widget node list */
         wibox_widgets_table_build(L, *wibox);