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86 lines
3.5 KiB
Plaintext
86 lines
3.5 KiB
Plaintext
# 00gnulib.m4 serial 8
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dnl Copyright (C) 2009-2021 Free Software Foundation, Inc.
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dnl This file is free software; the Free Software Foundation
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dnl gives unlimited permission to copy and/or distribute it,
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dnl with or without modifications, as long as this notice is preserved.
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dnl This file must be named something that sorts before all other
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dnl gnulib-provided .m4 files. It is needed until the clang fix has
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dnl been included in Autoconf.
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# The following definitions arrange to use a compiler option
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# -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
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# compiler is clang. Without it, clang implicitly declares "known"
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# library functions in C mode, but not in C++ mode, which would cause
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# Gnulib to omit a declaration and thus later produce an error in C++
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# mode. As of clang 9.0, these "known" functions are identified through
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# LIBBUILTIN invocations in the LLVM source file
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# llvm/tools/clang/include/clang/Basic/Builtins.def.
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# It's not possible to AC_REQUIRE the extra tests from AC_CHECK_DECL,
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# because AC_CHECK_DECL, like other Autoconf built-ins, is not supposed
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# to AC_REQUIRE anything: some configure.ac files have their first
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# AC_CHECK_DECL executed conditionally. Therefore append the extra tests
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# to AC_PROG_CC.
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AC_DEFUN([gl_COMPILER_CLANG],
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[
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dnl AC_REQUIRE([AC_PROG_CC])
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AC_CACHE_CHECK([whether the compiler is clang],
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[gl_cv_compiler_clang],
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[dnl Use _AC_COMPILE_IFELSE instead of AC_EGREP_CPP, to avoid error
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dnl "circular dependency of AC_LANG_COMPILER(C)" if AC_PROG_CC has
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dnl not yet been invoked.
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_AC_COMPILE_IFELSE(
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[AC_LANG_PROGRAM([[
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#ifdef __clang__
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barfbarf
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#endif
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]],[[]])
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],
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[gl_cv_compiler_clang=no],
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[gl_cv_compiler_clang=yes])
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])
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])
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AC_DEFUN([gl_COMPILER_PREPARE_CHECK_DECL],
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[
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dnl AC_REQUIRE([AC_PROG_CC])
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dnl AC_REQUIRE([gl_COMPILER_CLANG])
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AC_CACHE_CHECK([for compiler option needed when checking for declarations],
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[gl_cv_compiler_check_decl_option],
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[if test $gl_cv_compiler_clang = yes; then
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dnl Test whether the compiler supports the option
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dnl '-Werror=implicit-function-declaration'.
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save_ac_compile="$ac_compile"
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ac_compile="$ac_compile -Werror=implicit-function-declaration"
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dnl Use _AC_COMPILE_IFELSE instead of AC_COMPILE_IFELSE, to avoid a
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dnl warning "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
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_AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[]])],
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[gl_cv_compiler_check_decl_option='-Werror=implicit-function-declaration'],
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[gl_cv_compiler_check_decl_option=none])
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ac_compile="$save_ac_compile"
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else
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gl_cv_compiler_check_decl_option=none
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fi
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])
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if test "x$gl_cv_compiler_check_decl_option" != xnone; then
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ac_compile_for_check_decl="$ac_compile $gl_cv_compiler_check_decl_option"
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else
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ac_compile_for_check_decl="$ac_compile"
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fi
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])
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dnl Redefine _AC_CHECK_DECL_BODY so that it references ac_compile_for_check_decl
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dnl instead of ac_compile. If, for whatever reason, the override of AC_PROG_CC
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dnl in zzgnulib.m4 is inactive, use the original ac_compile.
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m4_define([_AC_CHECK_DECL_BODY],
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[ ac_save_ac_compile="$ac_compile"
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if test -n "$ac_compile_for_check_decl"; then
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ac_compile="$ac_compile_for_check_decl"
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fi]
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m4_defn([_AC_CHECK_DECL_BODY])[ ac_compile="$ac_save_ac_compile"
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])
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# gl_00GNULIB
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# -----------
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# Witness macro that this file has been included. Needed to force
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# Automake to include this file prior to all other gnulib .m4 files.
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AC_DEFUN([gl_00GNULIB])
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