1# 00gnulib.m4 serial 8
2dnl Copyright (C) 2009-2020 Free Software Foundation, Inc.
3dnl This file is free software; the Free Software Foundation
4dnl gives unlimited permission to copy and/or distribute it,
5dnl with or without modifications, as long as this notice is preserved.
6
7dnl This file must be named something that sorts before all other
8dnl gnulib-provided .m4 files.  It is needed until the clang fix has
9dnl been included in Autoconf.
10
11# The following definitions arrange to use a compiler option
12# -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
13# compiler is clang.  Without it, clang implicitly declares "known"
14# library functions in C mode, but not in C++ mode, which would cause
15# Gnulib to omit a declaration and thus later produce an error in C++
16# mode.  As of clang 9.0, these "known" functions are identified through
17# LIBBUILTIN invocations in the LLVM source file
18# llvm/tools/clang/include/clang/Basic/Builtins.def.
19# It's not possible to AC_REQUIRE the extra tests from AC_CHECK_DECL,
20# because AC_CHECK_DECL, like other Autoconf built-ins, is not supposed
21# to AC_REQUIRE anything: some configure.ac files have their first
22# AC_CHECK_DECL executed conditionally.  Therefore append the extra tests
23# to AC_PROG_CC.
24AC_DEFUN([gl_COMPILER_CLANG],
25[
26dnl AC_REQUIRE([AC_PROG_CC])
27  AC_CACHE_CHECK([whether the compiler is clang],
28    [gl_cv_compiler_clang],
29    [dnl Use _AC_COMPILE_IFELSE instead of AC_EGREP_CPP, to avoid error
30     dnl "circular dependency of AC_LANG_COMPILER(C)" if AC_PROG_CC has
31     dnl not yet been invoked.
32     _AC_COMPILE_IFELSE(
33        [AC_LANG_PROGRAM([[
34           #ifdef __clang__
35           barfbarf
36           #endif
37           ]],[[]])
38        ],
39        [gl_cv_compiler_clang=no],
40        [gl_cv_compiler_clang=yes])
41    ])
42])
43AC_DEFUN([gl_COMPILER_PREPARE_CHECK_DECL],
44[
45dnl AC_REQUIRE([AC_PROG_CC])
46dnl AC_REQUIRE([gl_COMPILER_CLANG])
47  AC_CACHE_CHECK([for compiler option needed when checking for declarations],
48    [gl_cv_compiler_check_decl_option],
49    [if test $gl_cv_compiler_clang = yes; then
50       dnl Test whether the compiler supports the option
51       dnl '-Werror=implicit-function-declaration'.
52       save_ac_compile="$ac_compile"
53       ac_compile="$ac_compile -Werror=implicit-function-declaration"
54       dnl Use _AC_COMPILE_IFELSE instead of AC_COMPILE_IFELSE, to avoid a
55       dnl warning "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
56       _AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[]])],
57         [gl_cv_compiler_check_decl_option='-Werror=implicit-function-declaration'],
58         [gl_cv_compiler_check_decl_option=none])
59       ac_compile="$save_ac_compile"
60     else
61       gl_cv_compiler_check_decl_option=none
62     fi
63    ])
64  if test "x$gl_cv_compiler_check_decl_option" != xnone; then
65    ac_compile_for_check_decl="$ac_compile $gl_cv_compiler_check_decl_option"
66  else
67    ac_compile_for_check_decl="$ac_compile"
68  fi
69])
70dnl Redefine _AC_CHECK_DECL_BODY so that it references ac_compile_for_check_decl
71dnl instead of ac_compile.  If, for whatever reason, the override of AC_PROG_CC
72dnl in zzgnulib.m4 is inactive, use the original ac_compile.
73m4_define([_AC_CHECK_DECL_BODY],
74[  ac_save_ac_compile="$ac_compile"
75  if test -n "$ac_compile_for_check_decl"; then
76    ac_compile="$ac_compile_for_check_decl"
77  fi]
78m4_defn([_AC_CHECK_DECL_BODY])[  ac_compile="$ac_save_ac_compile"
79])
80
81# gl_00GNULIB
82# -----------
83# Witness macro that this file has been included.  Needed to force
84# Automake to include this file prior to all other gnulib .m4 files.
85AC_DEFUN([gl_00GNULIB])
86