From d7475d4073b5ff63207b010ec1249dfb64374cf6 Mon Sep 17 00:00:00 2001
From: Rob Browning <rlb@defaultvalue.org>
Date: Sat, 1 Mar 2025 11:24:19 -0600
Subject: [PATCH] configure.ac: enable -ffat-lto-objects with -flto when
 available

Without -ffat-lto-objects libguile.a ends up with no symbols, visible
via "nm t libguile.a".
cf. https://lintian.debian.org/tags/no-code-sections.html

* configure.ac: enable -ffat-lto-objects with -flto when available.
---
 NEWS         |  3 +++
 configure.ac | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/NEWS b/NEWS
index 7429127db..053f46f0a 100644
--- a/NEWS
+++ b/NEWS
@@ -90,6 +90,9 @@ every line in a file.
    This used to trigger a warning, unduly.
 ** SRFI-19: 'date->string' converter ~V is now correctly interpreted
    (<https://bugs.gnu.org/74841>)
+** When -flto is enabled configure now adds -ffat-lto-objects if it exists
+   Otherwise libguile.a can end up with no code.
+   https://lintian.debian.org/tags/no-code-sections.html
 
 
 Changes in 3.0.10 (since 3.0.9)
diff --git a/configure.ac b/configure.ac
index af9176b46..f3a05ec70 100644
--- a/configure.ac
+++ b/configure.ac
@@ -98,6 +98,24 @@ else
   AC_MSG_RESULT([no])
 fi
 
+# https://lintian.debian.org/tags/no-code-sections.html
+if test "$LTO_CFLAGS"; then
+  if ! test "$LTO_CFLAGS" = -flto; then # currently expected below
+    AC_MSG_ERROR([LTO_CFLAGS wasn't just -flto])
+  fi
+  AC_MSG_CHECKING([whether the compiler supports -ffat-lto-objects])
+  old_CFLAGS="$CFLAGS"
+  LTO_CFLAGS="-flto -ffat-lto-objects"
+  CFLAGS="$CFLAGS $LTO_CFLAGS"
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([int foo;], [])],, [LTO_CFLAGS=-flto])
+  CFLAGS="$old_CFLAGS"
+  if test -n "$LTO_CFLAGS"; then
+    AC_MSG_RESULT([yes])
+  else
+    AC_MSG_RESULT([no])
+  fi
+fi
+
 AC_ARG_ENABLE(lto,
   [AS_HELP_STRING([--enable-lto]
                   [enable link-time optimization for libguile])],