Module func 

Auxiliary functions to manipulate prototypes and closures.

Port of reference/lua-5.4.7/src/lfunc.c (295 lines, 16 functions). The companion header lfunc.h is merged here per PORTING.md §1.

Design notes

The C implementation uses two intrusive linked lists managed through pointer fields embedded in stack slots and upvalue objects:

• openupval: a singly-linked list of UpVals sorted by stack level (highest first), threaded through UpVal.u.open.next / .previous.
• tbclist: a to-be-closed variable list encoded as unsigned short delta offsets stored inside StackValue.tbclist.delta.

Both are replaced in the Rust port:

• openupval → LuaState.openupval: Vec<GcRef<UpVal>> (descending by StackIdx).
• tbclist → LuaState.tbclist: Vec<StackIdx> (back = most recent entry).

The delta-encoding machinery (MAXDELTA, dummy nodes) is an artifact of the u16 delta field and is entirely superseded by the Vec<StackIdx> model.

Structs

CallInfoIdx

Index into the call-info stack.

StackIdx

Index into the Lua value stack. Never a pointer or borrow. Stack reallocates; only indices are stable across mutations.