1# 00gnulib.m4 serial 7
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.  The first part is needed until such time
9dnl as we can assume Autoconf 2.64, with its improved AC_DEFUN_ONCE and
10dnl m4_divert semantics.  The second part is needed until the clang fix
11dnl has been included in Autoconf.
12
13# Until autoconf 2.63, handling of the diversion stack required m4_init
14# to be called first; but this does not happen with aclocal.  Wrapping
15# the entire execution in another layer of the diversion stack fixes this.
16# Worse, prior to autoconf 2.62, m4_wrap depended on the underlying m4
17# for whether it was FIFO or LIFO; in order to properly balance with
18# m4_init, we need to undo our push just before anything wrapped within
19# the m4_init body.  The way to ensure this is to wrap both sides of
20# m4_init with a one-shot macro that does the pop at the right time.
21m4_ifndef([_m4_divert_diversion],
22[m4_divert_push([KILL])
23m4_define([gl_divert_fixup], [m4_divert_pop()m4_define([$0])])
24m4_define([m4_init],
25  [gl_divert_fixup()]m4_defn([m4_init])[gl_divert_fixup()])])
26
27
28# AC_DEFUN_ONCE([NAME], VALUE)
29# ----------------------------
30# Define NAME to expand to VALUE on the first use (whether by direct
31# expansion, or by AC_REQUIRE), and to nothing on all subsequent uses.
32# Avoid bugs in AC_REQUIRE in Autoconf 2.63 and earlier.  This
33# definition is slower than the version in Autoconf 2.64, because it
34# can only use interfaces that existed since 2.59; but it achieves the
35# same effect.  Quoting is necessary to avoid confusing Automake.
36m4_version_prereq([2.63.263], [],
37[m4_define([AC][_DEFUN_ONCE],
38  [AC][_DEFUN([$1],
39    [AC_REQUIRE([_gl_DEFUN_ONCE([$1])],
40      [m4_indir([_gl_DEFUN_ONCE([$1])])])])]dnl
41[AC][_DEFUN([_gl_DEFUN_ONCE([$1])], [$2])])])
42
43# The following definitions arrange to use a compiler option
44# -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
45# compiler is clang.  Without it, clang implicitly declares "known"
46# library functions in C mode, but not in C++ mode, which would cause
47# Gnulib to omit a declaration and thus later produce an error in C++
48# mode.  As of clang 9.0, these "known" functions are identified through
49# LIBBUILTIN invocations in the LLVM source file
50# llvm/tools/clang/include/clang/Basic/Builtins.def.
51# It's not possible to AC_REQUIRE the extra tests from AC_CHECK_DECL,
52# because AC_CHECK_DECL, like other Autoconf built-ins, is not supposed
53# to AC_REQUIRE anything: some configure.ac files have their first
54# AC_CHECK_DECL executed conditionally.  Therefore append the extra tests
55# to AC_PROG_CC.
56AC_DEFUN([gl_COMPILER_CLANG],
57[
58dnl AC_REQUIRE([AC_PROG_CC])
59  AC_CACHE_CHECK([whether the compiler is clang],
60    [gl_cv_compiler_clang],
61    [dnl Use _AC_COMPILE_IFELSE instead of AC_EGREP_CPP, to avoid error
62     dnl "circular dependency of AC_LANG_COMPILER(C)" if AC_PROG_CC has
63     dnl not yet been invoked.
64     _AC_COMPILE_IFELSE(
65        [AC_LANG_PROGRAM([[
66           #ifdef __clang__
67           barfbarf
68           #endif
69           ]],[[]])
70        ],
71        [gl_cv_compiler_clang=no],
72        [gl_cv_compiler_clang=yes])
73    ])
74])
75AC_DEFUN([gl_COMPILER_PREPARE_CHECK_DECL],
76[
77dnl AC_REQUIRE([AC_PROG_CC])
78dnl AC_REQUIRE([gl_COMPILER_CLANG])
79  AC_CACHE_CHECK([for compiler option needed when checking for declarations],
80    [gl_cv_compiler_check_decl_option],
81    [if test $gl_cv_compiler_clang = yes; then
82       dnl Test whether the compiler supports the option
83       dnl '-Werror=implicit-function-declaration'.
84       save_ac_compile="$ac_compile"
85       ac_compile="$ac_compile -Werror=implicit-function-declaration"
86       dnl Use _AC_COMPILE_IFELSE instead of AC_COMPILE_IFELSE, to avoid a
87       dnl warning "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
88       _AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[]])],
89         [gl_cv_compiler_check_decl_option='-Werror=implicit-function-declaration'],
90         [gl_cv_compiler_check_decl_option=none])
91       ac_compile="$save_ac_compile"
92     else
93       gl_cv_compiler_check_decl_option=none
94     fi
95    ])
96  if test "x$gl_cv_compiler_check_decl_option" != xnone; then
97    ac_compile_for_check_decl="$ac_compile $gl_cv_compiler_check_decl_option"
98  else
99    ac_compile_for_check_decl="$ac_compile"
100  fi
101])
102dnl Redefine _AC_CHECK_DECL_BODY so that it references ac_compile_for_check_decl
103dnl instead of ac_compile.  If, for whatever reason, the override of AC_PROG_CC
104dnl in zzgnulib.m4 is inactive, use the original ac_compile.
105m4_define([_AC_CHECK_DECL_BODY],
106[  ac_save_ac_compile="$ac_compile"
107  if test -n "$ac_compile_for_check_decl"; then
108    ac_compile="$ac_compile_for_check_decl"
109  fi]
110m4_defn([_AC_CHECK_DECL_BODY])[  ac_compile="$ac_save_ac_compile"
111])
112
113# gl_00GNULIB
114# -----------
115# Witness macro that this file has been included.  Needed to force
116# Automake to include this file prior to all other gnulib .m4 files.
117AC_DEFUN([gl_00GNULIB])
118