4 files changed, 129 insertions, 14 deletions

diff --git a/src/lanes.c b/src/lanes.c
index eebe06a..3e906c0 100644
--- a/src/lanes.c
+++ b/src/lanes.c
@@ -2303,6 +2303,7 @@ static const struct luaL_reg lanes_functions [] = {
     {"linda", LG_linda},
     {"now_secs", LG_now_secs},
     {"wakeup_conv", LG_wakeup_conv},
+    {"nameof", luaG_nameof},
     {"_single", LG__single},
     {NULL, NULL}
 };
diff --git a/src/lanes.lua b/src/lanes.lua
index 5aeeaf4..d1082af 100644
--- a/src/lanes.lua
+++ b/src/lanes.lua
@@ -564,6 +564,7 @@ end
         lanes.gen = gen
         lanes.linda = mm.linda
         lanes.cancel_error = mm.cancel_error
+        lanes.nameof = mm.nameof
         lanes.timer = timer
         lanes.genlock = genlock
         lanes.genatomic = genatomic
diff --git a/src/tools.c b/src/tools.c
index ee2a1ca..65c70bf 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -1200,38 +1200,149 @@ static void push_cached_func( lua_State *L2, uint_t L2_cache_i, lua_State *L, ui
 }
 
 /*
+ * Return some name helping to identify an object
+ */
+int discover_object_name_recur( lua_State* L, int _shortest, int _length)
+{
+        int const what = 1;                                     // o "r" {c} {fqn} ... {?}
+        int const result = 2;
+        int const cache = 3;
+        int const fqn = 4;
+        // no need to scan this table if the name we will discover is longer than one we already know
+        if( _shortest <= _length + 1)
+        {
+                return _shortest;
+        }
+        STACK_GROW( L, 3);
+        STACK_CHECK(L)
+        // stack top contains the table to search in
+        lua_pushvalue( L, -1);                                  // o "r" {c} {fqn} ... {?} {?}
+        lua_rawget( L, cache);                                  // o "r" {c} {fqn} ... {?} nil/1
+        // if table is already visited, we are done
+        if( !lua_isnil( L, -1))
+        {
+                lua_pop( L, 1);                                       // o "r" {c} {fqn} ... {?}
+                return _shortest;
+        }
+        // examined table is not in the cache, add it now
+        lua_pop( L, 1);                                         // o "r" {c} {fqn} ... {?}
+        lua_pushvalue( L, -1);                                  // o "r" {c} {fqn} ... {?} {?}
+        lua_pushinteger( L, 1);                                 // o "r" {c} {fqn} ... {?} {?} 1
+        lua_rawset( L, cache);                                  // o "r" {c} {fqn} ... {?}
+        // scan table contents
+        lua_pushnil( L);                                        // o "r" {c} {fqn} ... {?} nil
+        while( lua_next( L, -2))                                // o "r" {c} {fqn} ... {?} k v
+        {
+                //char const *const key = lua_tostring( L, -2); // only for debugging (BEWARE, IT MAY CHANGE THE VALUE IF IT IS CONVERTIBLE, AND WRECK THE LOOP ITERATION PROCESS!)
+                // append key name to fqn stack
+                ++ _length;
+                lua_pushvalue( L, -2);                                // o "r" {c} {fqn} ... {?} k v k
+                lua_rawseti( L, fqn, _length);                        // o "r" {c} {fqn} ... {?} k v
+                if( lua_rawequal( L, -1, what)) // is it what we are looking for?
+                {
+                        // update shortest name
+                        if( _length < _shortest)
+                        {
+                                _shortest = _length;
+                                luaG_pushFQN( L, fqn, _length);                   // o "r" {c} {fqn} ... {?} k v "fqn"
+                                lua_replace( L, result);                          // o "r" {c} {fqn} ... {?} k v
+                        }
+                        // no need to search further at this level
+                        lua_pop( L, 2);                                     // o "r" {c} {fqn} ... {?}
+                        break;
+                }
+                else if( lua_istable( L, -1))
+                {
+                        _shortest = discover_object_name_recur( L, _shortest, _length);
+                }
+                // make ready for next iteration
+                lua_pop( L, 1);                                       // o "r" {c} {fqn} ... {?} k
+                // remove name from fqn stack
+                lua_pushnil( L);                                      // o "r" {c} {fqn} ... {?} k nil
+                lua_rawseti( L, fqn, _length);                        // o "r" {c} {fqn} ... {?} k
+                -- _length;
+        }                                                       // o "r" {c} {fqn} ... {?}
+        // remove the visited table from the cache, in case a shorter path to the searched object exists
+        lua_pushvalue( L, -1);                                  // o "r" {c} {fqn} ... {?} {?}
+        lua_pushnil( L);                                        // o "r" {c} {fqn} ... {?} {?} nil
+        lua_rawset( L, cache);                                  // o "r" {c} {fqn} ... {?}
+        STACK_END( L, 0)
+        return _shortest;
+}
+
+/*
+ * "type", "name" = lanes.nameof( o)
+ */
+int luaG_nameof( lua_State* L)
+{
+        int what = lua_gettop( L);
+        if( what > 1)
+        {
+                luaL_argerror( L, what, "too many arguments.");
+        }
+
+        // numbers, strings, booleans and nil can't be identified
+        if( lua_type( L, 1) < LUA_TTABLE)
+        {
+                lua_pushstring( L, luaL_typename( L, 1));             // o "type"
+                lua_insert( L, -2);                                   // "type" o
+                return 2;
+        }
+        STACK_GROW( L, 4);
+        // this slot will contain the shortest name we found when we are done
+        lua_pushnil( L);                                        // o nil
+        // push a cache that will contain all already visited tables
+        lua_newtable( L);                                       // o nil {c}
+        // push a table whose contents are strings that, when concatenated, produce unique name
+        lua_newtable( L);                                       // o nil {c} {fqn}
+        // this is where we start the search
+        lua_pushvalue( L, LUA_GLOBALSINDEX);                    // o nil {c} {fqn} _G
+        (void) discover_object_name_recur( L, 6666, 0);
+        lua_pop( L, 3);                                         // o "result"
+        lua_pushstring( L, luaL_typename( L, 1));               // o "result" "type"
+        lua_replace( L, -3);                                    // "type" "result"
+        return 2;
+}
+
+/*
 * Push a looked-up native/LuaJIT function.
 */
 static void lookup_native_func( lua_State *L2, lua_State *L, uint_t i)
 {
-        char const *fqn;
+        char const *fqn;                                         // L                        // L2
         size_t len;
-        _ASSERT_L( L, lua_isfunction( L, i));
+        _ASSERT_L( L, lua_isfunction( L, i));                    // ... f ...
         STACK_CHECK( L)
-        STACK_CHECK( L2)
         // fetch the name from the source state's lookup table
-        lua_getfield( L, LUA_REGISTRYINDEX, LOOKUP_KEY);         // {}
+        lua_getfield( L, LUA_REGISTRYINDEX, LOOKUP_KEY);         // ... f ... {}
         _ASSERT_L( L, lua_istable( L, -1));
-        lua_pushvalue( L, i);                                    // {} f
-        lua_rawget( L, -2);                                      // {} "f.q.n"
+        lua_pushvalue( L, i);                                    // ... f ... {} f
+        lua_rawget( L, -2);                                      // ... f ... {} "f.q.n"
         fqn = lua_tolstring( L, -1, &len);
+        // popping doesn't invalidate the pointer since this is an interned string gotten from the lookup database
+        lua_pop( L, 2);                                          // ... f ...
         if( !fqn)
         {
-                luaL_error( L, "function not found in origin transfer database.");
+                lua_pushvalue( L, i);                                  // ... f ... f
+                // try to discover the name of the function we want to send
+                luaG_nameof( L);                                       // ... f ... "type" "name"
+                (void) luaL_error( L, "%s %s not found in origin transfer database.", lua_tostring( L, -2), lua_tostring( L, -1));
+                return;
         }
+        STACK_END( L, 0)
         // push the equivalent function in the destination's stack, retrieved from the lookup table
-        lua_getfield( L2, LUA_REGISTRYINDEX, LOOKUP_KEY);                               // {}
+        STACK_CHECK( L2)
+        lua_getfield( L2, LUA_REGISTRYINDEX, LOOKUP_KEY);                                    // {}
         _ASSERT_L( L2, lua_istable( L2, -1));
-        lua_pushlstring( L2, fqn, len);                                                 // {} "f.q.n"
-        lua_pop( L, 2);                                          //
-        lua_rawget( L2, -2);                                                            // {} f
+        lua_pushlstring( L2, fqn, len);                                                      // {} "f.q.n"
+        lua_rawget( L2, -2);                                                                 // {} f
         if( !lua_isfunction( L2, -1))
         {
-                luaL_error( L, "function %s not found in destination transfer database.", fqn);
+                (void) luaL_error( L, "function %s not found in destination transfer database.", fqn);
+                return;
         }
-        lua_remove( L2, -2);                                                            // f
+        lua_remove( L2, -2);                                                                 // f
         STACK_END( L2, 1)
-        STACK_END( L, 0)
 }
 
 #define LOG_FUNC_INFO 0
diff --git a/src/tools.h b/src/tools.h
index 67f9874..b8dc362 100644
--- a/src/tools.h
+++ b/src/tools.h
@@ -65,6 +65,8 @@ void luaG_push_proxy( lua_State *L, luaG_IdFunction idfunc, DEEP_PRELUDE *deep_u
 int luaG_inter_copy( lua_State *L, lua_State *L2, uint_t n);
 int luaG_inter_move( lua_State *L, lua_State *L2, uint_t n);
 
+int luaG_nameof( lua_State* L);
+
 // Lock for reference counter inc/dec locks (to be initialized by outside code)
 //
 extern MUTEX_T deep_lock;