Reenable console completion help

[NicksWorld]

The code has been updated to properly account for potential items on the lua stack.

[dhthwy]

I would still suggest wrapping this in a

lua_istable() block

to prevent hangs and crashes (print an error message instead) as there is a very real possibility it won't be a table -- other stuff can be put on the stack in the future and top + 1 won't work anymore.

And I'm not sure if there's supposed to be things on the stack still, so that may get fixed and potentially cause a problem.

[dhthwy]

nevermind. I suppose top + 1 will handle those case. Though, still not a bad idea to wrap in lua_istable(). It's better to print an error than to crash or hang.

[lethosor]

This only works because the stack size increases by a net of 1 item (the return value from helpdb.get_commands()) between when top is initialized and when this line is reached. In between, there are several stack operations (helpdb is pushed and popped internally to PushModulePublic, and helpdb.get_commands is pushed by PushModulePublic and popped by SafeCall). In my experience, there is some risk that someone coming along later could change the intervening logic to push more things on the stack without popping them, which is legal since this function is using a StackUnwinder, but would break this index.

So I would suggest

Suggested change

	Lua::GetVector(L, commands, top + 1);
	Lua::GetVector(L, commands, -1);

which is equivalent to Lua::GetVector(L, commands, lua_gettop(L) - 1); and will always give you the top-most item on the stack, which is what you want here.

[lethosor]

You mentioned on Discord that -1 won't work because GetVector itself manipulates the stack before using the input index. The patch you posted would fix that.

@@ -449,11 +450,12 @@ void get_commands(color_ostream &con, std::vector<std::string> &commands) {
         return;
     }

-    if (!Lua::SafeCall(con, L, 0, 1)) {
+    if (!Lua::SafeCall(con, L, 0, 1) || !lua_istable(L, -1)) {
         con.printerr("Failed Lua call to helpdb.get_commands.\n");
+        return;
     }

-    Lua::GetVector(L, commands, top + 1);
+    Lua::GetVector(L, commands, -1);
 }

 static bool try_autocomplete(color_ostream &con, const std::string &first, std::string &completed)
diff --git a/library/LuaTools.cpp b/library/LuaTools.cpp
index 08b90bd61..fb4a593ff 100644
--- a/library/LuaTools.cpp
+++ b/library/LuaTools.cpp
@@ -122,6 +122,9 @@ void DFHack::Lua::Push(lua_State *state, const df::coord2d &pos)

 void DFHack::Lua::GetVector(lua_State *state, std::vector<std::string> &pvec, int idx)
 {
+    // Allow usage of relative indexes in arg
+    idx = lua_absindex(state, idx);
+
     luaL_checktype(state, idx, LUA_TTABLE);
     lua_pushnil(state);   // first key
     while (lua_next(state, idx) != 0)