patch 9.0.1908: undefined behaviour upper/lower function ptrs Commit: https://github.com/vim/vim/commit/d25021cf036c63d539f845a1ee05b03ea21d61ff Author: Yee Cheng Chin <ychin.git@gmail.com> Date: Mon Sep 18 19:51:56 2023 +0200 patch 9.0.1908: undefined behaviour upper/lower function ptrs Problem: undefined behaviour upper/lower function ptrs Solution: Fix UBSAN error in regexp and simplify upper/lowercase modifier code The implementation of \u / \U / \l / \L modifiers in the substitute command relies on remembering the state by setting function pointers on func_all/func_one in the code. The code signature of `fptr_T` is supposed to return void* (due to C function signatures not being able to return itself due to type recursion), and the definition of the functions (e.g. to_Upper) didn't follow this rule, and so the code tries to cast functions of different signatures, resulting in undefined behavior error under UBSAN in Clang 17. See #12745. We could just fix `do_Upper`/etc to just return void*, which would fix the problem. However, these functions actually do not need to return anything at all. It used to be the case that there was only one pointer "func" to store the pointer, which is why the function needs to either return itself or NULL to indicate whether it's a one time or ongoing modification. However, c2c355df6f094cdb9e599fd395a78c14486ec697 (7.3.873) already made that obsolete by introducing `func_one` and `func_all` to store one-time and ongoing operations separately, so these functions don't actually need to return anything anymore because it's implicit whether it's a one-time or ongoing operation. Simplify the code to reflect that. closes: #13117 Signed-off-by: Christian Brabandt <cb@256bit.org> Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>