Prohibit implicit C function declarations
Issue #27659: use -Werror=implicit-function-declaration when possible (GCC and
Clang, but it depends on the compiler version).
Patch written by Chi Hsuan Yen.
diff --git a/configure b/configure
index a624d1c..1126372 100755
--- a/configure
+++ b/configure
@@ -7242,6 +7242,47 @@
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_enable_unreachable_code_warning" >&5
$as_echo "$ac_cv_enable_unreachable_code_warning" >&6; }
+ { $as_echo "$as_me:${as_lineno-$LINENO}: checking if we can make implicit function declaration an error in $CC" >&5
+$as_echo_n "checking if we can make implicit function declaration an error in $CC... " >&6; }
+ ac_save_cc="$CC"
+ CC="$CC -Werror=implicit-function-declaration"
+ if ${ac_cv_enable_implicit_function_declaration_error+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+
+
+int
+main ()
+{
+
+ ;
+ return 0;
+}
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+ ac_cv_enable_implicit_function_declaration_error=yes
+
+else
+
+ ac_cv_enable_implicit_function_declaration_error=no
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+
+ CC="$ac_save_cc"
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_enable_implicit_function_declaration_error" >&5
+$as_echo "$ac_cv_enable_implicit_function_declaration_error" >&6; }
+
+ if test $ac_cv_enable_implicit_function_declaration_error = yes
+ then
+ CFLAGS_NODIST="$CFLAGS_NODIST -Werror=implicit-function-declaration"
+ fi
+
# if using gcc on alpha, use -mieee to get (near) full IEEE 754
# support. Without this, treatment of subnormals doesn't follow
# the standard.