From 1b005039cbe27964800c147f224360054683a129 Mon Sep 17 00:00:00 2001
From: Alexander Sulfrian <a.sulfrian@fu-berlin.de>
Date: Tue, 3 Mar 2026 17:23:15 +0100
Subject: [PATCH] configure: Fix zlib detection

The configure script failed to detect zlib. Even when the required
libraries and development files are installed, the configure outputted
the following:

> checking for zlib package... no

This issue occurs when using gcc-14, which treats some warnings as
errors. Below is the relevant part of the config.log preceding this
patch:

> configure:5472: checking for zlib package
> configure:5500: gcc -E  conftest.c
> configure:5500: $? = 0
> configure:5537: gcc -o conftest -g -O2   conftest.c -lz -lcrypt  >&5
> conftest.c: In function 'main':
> conftest.c:90:1: error: implicit declaration of function 'inflate' [-Wimplicit-function-declaration]
>    90 | inflate()
>       | ^~~~~~~
> configure:5537: $? = 1
---
 support/configure    | 14 ++++++++++++--
 support/configure.in |  2 +-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/support/configure b/support/configure
index a6a58ded..c375a6b7 100755
--- a/support/configure
+++ b/support/configure
@@ -5526,10 +5526,20 @@ LIBS="-lz $LIBS"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.
+   The 'extern "C"' is for builds by C++ compilers;
+   although this is not generally supported in C code supporting it here
+   has little cost and some practical benefit (sr 110532).  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char inflate(void);
 int
-main ()
+main (void)
 {
-inflate()
+return inflate();
   ;
   return 0;
 }
diff --git a/support/configure.in b/support/configure.in
index a90ccd20..053d2065 100644
--- a/support/configure.in
+++ b/support/configure.in
@@ -82,7 +82,7 @@ irc_zlib_include=],[for irc_dir in "$irc_zlib_include" \
 ])
 irc_save_LIBS="$LIBS"
 LIBS="-lz $LIBS"
-AC_LINK_IFELSE([AC_LANG_PROGRAM([[]], [[inflate()]])],[no_zlib_library=
+AC_LINK_IFELSE([AC_LANG_CALL([], [inflate])],[no_zlib_library=
 irc_zlib_library=
 LIBS="$irc_save_LIBS"],[LIBS="$irc_save_LIBS"
 for irc_dir in "$irc_zlib_library" \