[BUG] configure script will fail silently with clang-16

[tastytea]

Describe the bug

The module doesn't build with (simulated) clang-16 because ./configure silently fails. Running make afterwards does not produce fzftab.so.

• Clang 16 (to be released appx. March 2023) will make the following default errors:

  • -Werror=implicit-function-declaration
  • -Werror=implicit-int
  • -Werror=int-conversion (this is in Clang 15, actually)
  • -Werror=incompatible-function-pointer-types (GCC does not have a specific equivalent error, use -Werror=incompatible-pointer-types instead when testing)

• GCC 14 (to be released appx. May 2024) is likely to do the same.

— https://wiki.gentoo.org/wiki/Modern_C_porting#What_changed.3F

I simulated building with clang-16 like this:

% CC=clang \
  CFLAGS="-Werror=implicit-function-declaration \
          -Werror=implicit-int \
          -Werror=incompatible-function-pointer-types" \
  ./configure --disable-gdbm --without-tcsetpgrp
% make

diffing the config.log with clang-15 with the one with simulated clang-16 and greping for '^\+.*error:' shows 64 new errors.

I can make sure:

• I am using the latest version of fzf-tab
• this is the minimal zshrc which can reproduce this bug
• fzf-tab is loaded after compinit
• fzf-tab is loaded after plugins which will wrap Tab, like junegunn/fzf/completion.zsh
• fzf-tab is loaded before zsh-autosuggestions, zsh-syntax-highlighting and fast-syntax-highlighting.

To Reproduce

Steps to reproduce the behavior:

1. Run CC=clang CFLAGS="-Werror=implicit-function-declaration -Werror=implicit-int -Werror=incompatible-function-pointer-types" ./configure --disable-gdbm --without-tcsetpgrp in ./modules
2. Run make
3. ./Src/aloxaf/fzftab.so does not exist

Expected behavior

./configure uses valid C code.

Environment:

• OS: Gentoo Linux
• zsh version: 5.9

Logs

• config.log with clang-15
• config.log with simulated clang-16
• diff -u config_clang15.log config_clang16.log | grep '^\+.*error:'

Additional context

• https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213