[ovs-dev] [PATCH 4/5] Automatically verify that OVS header files work OK in C++ also.
Russell Bryant
russell at ovn.org
Mon Jul 31 20:44:10 UTC 2017
On Mon, Jul 31, 2017 at 4:33 PM, Ben Pfaff <blp at ovn.org> wrote:
> On Mon, Jul 31, 2017 at 01:05:32PM -0700, Ben Pfaff wrote:
>> On Mon, Jul 31, 2017 at 03:50:59PM -0400, Russell Bryant wrote:
>> > On Sun, Jul 30, 2017 at 10:54 PM, Ben Pfaff <blp at ovn.org> wrote:
>> > > This should help address a recurring problem.
>> > >
>> > > Signed-off-by: Ben Pfaff <blp at ovn.org>
>> > > ---
>> > > .travis.yml | 1 +
>> > > Makefile.am | 1 +
>> > > configure.ac | 2 ++
>> > > include/openvswitch/automake.mk | 14 ++++++++++++++
>> > > m4/openvswitch.m4 | 21 +++++++++++++++++++++
>> > > 5 files changed, 39 insertions(+)
>> >
>> > Why does this patch depend on libboost? It looks like it's only used
>> > when building a test C++ program in configure. We could build a test
>> > C++ program without the dependency, right?
>>
>> It's because of include/openvswitch/compiler.h, which has:
>>
>> #elif defined(__cplusplus)
>> #include <boost/static_assert.hpp>
>> #define BUILD_ASSERT BOOST_STATIC_ASSERT
>> #define BUILD_ASSERT_DECL BOOST_STATIC_ASSERT
>>
Ah, sorry ...
>> We could probably define our own C++-compatible static assert without
>> boost. It looks like C++11 and later has a built-in static_assert:
>> http://en.cppreference.com/w/cpp/language/static_assert
>>
>> Any idea whether it's reasonable to assume C++11 support these days?
I don't know, but that seems pretty reasonable to me.
I suppose if it becomes an issue, we could re-add the boost version as
an optional dependency that would get used only if C++11 wasn't
available?
Acked-by: Russell Bryant <russell at ovn.org>
>
> Here's a version of the patch that gets rid of the boost dependency. It
> adds a C++11 dependency instead.
>
> --8<--------------------------cut here-------------------------->8--
>
> From: Ben Pfaff <blp at ovn.org>
> Date: Mon, 31 Jul 2017 13:31:43 -0700
> Subject: [PATCH] Automatically verify that OVS header files work OK in C++
> also.
>
> This should help address a recurring problem.
>
> Signed-off-by: Ben Pfaff <blp at ovn.org>
> ---
> Makefile.am | 1 +
> configure.ac | 2 +
> include/openflow/openflow-common.h | 3 +-
> include/openvswitch/automake.mk | 14 +
> include/openvswitch/compiler.h | 5 +-
> m4/ax_cxx_compile_stdcxx.m4 | 982 +++++++++++++++++++++++++++++++++++++
> m4/openvswitch.m4 | 16 +
> 7 files changed, 1018 insertions(+), 5 deletions(-)
> create mode 100644 m4/ax_cxx_compile_stdcxx.m4
>
> diff --git a/Makefile.am b/Makefile.am
> index 9679379defef..373ef6e9189f 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -108,6 +108,7 @@ MAN_ROOTS =
> noinst_DATA =
> noinst_HEADERS =
> lib_LTLIBRARIES =
> +noinst_LTLIBRARIES =
> noinst_man_MANS =
> noinst_PROGRAMS =
> noinst_SCRIPTS =
> diff --git a/configure.ac b/configure.ac
> index 194c4b92ee34..093b6ffed50e 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -23,6 +23,7 @@ AM_INIT_AUTOMAKE([tar-pax])
>
> AC_PROG_CC_C99
> AM_PROG_CC_C_O
> +AC_PROG_CXX
> AC_PROG_CPP
> AC_PROG_MKDIR_P
> AC_PROG_FGREP
> @@ -135,6 +136,7 @@ OVS_CHECK_POSIX_AIO
> OVS_CHECK_PTHREAD_SET_NAME
> OVS_CHECK_LINUX_HOST
> OVS_LIBTOOL_VERSIONS
> +OVS_CHECK_CXX
> AX_FUNC_POSIX_MEMALIGN
>
> OVS_CHECK_INCLUDE_NEXT([stdio.h string.h])
> diff --git a/include/openflow/openflow-common.h b/include/openflow/openflow-common.h
> index 410f392d20cd..5f1e22589ced 100644
> --- a/include/openflow/openflow-common.h
> +++ b/include/openflow/openflow-common.h
> @@ -60,8 +60,7 @@
> extern int (*build_assert(void))[ sizeof(struct { \
> unsigned int build_assert_failed : (EXPR) ? 1 : -1; })]
> #else /* __cplusplus */
> -#include <boost/static_assert.hpp>
> -#define OFP_ASSERT BOOST_STATIC_ASSERT
> +#define OFP_ASSERT(EXPR) static_assert(EXPR, "assertion failed")
> #endif /* __cplusplus */
>
> /* Version number:
> diff --git a/include/openvswitch/automake.mk b/include/openvswitch/automake.mk
> index 699d9d74ecd0..74b31acfa66b 100644
> --- a/include/openvswitch/automake.mk
> +++ b/include/openvswitch/automake.mk
> @@ -30,3 +30,17 @@ openvswitchinclude_HEADERS = \
> include/openvswitch/version.h \
> include/openvswitch/vconn.h \
> include/openvswitch/vlog.h
> +
> +if HAVE_CXX
> +# OVS does not use C++ itself, but it provides public header files
> +# that a C++ compiler should accept, so when --enable-Werror is in
> +# effect and a C++ compiler is available, we build a C++ source file
> +# that #includes all the public headers, as a way to ensure that they
> +# are acceptable as C++.
> +noinst_LTLIBRARIES += include/openvswitch/libcxxtest.la
> +nodist_include_openvswitch_libcxxtest_la_SOURCES = include/openvswitch/cxxtest.cc
> +include/openvswitch/cxxtest.cc: include/openvswitch/automake.mk
> + $(AM_V_GEN)for header in $(openvswitchinclude_HEADERS); do \
> + echo $$header; \
> + done | sed 's,^include/\(.*\)$$,#include <\1>,' > $@
> +endif
> diff --git a/include/openvswitch/compiler.h b/include/openvswitch/compiler.h
> index 0dc8636add33..0076ad763578 100644
> --- a/include/openvswitch/compiler.h
> +++ b/include/openvswitch/compiler.h
> @@ -244,9 +244,8 @@
> #define BUILD_ASSERT(EXPR) ((void) 0)
> #define BUILD_ASSERT_DECL(EXPR) extern int (*build_assert(void))[1]
> #elif defined(__cplusplus)
> -#include <boost/static_assert.hpp>
> -#define BUILD_ASSERT BOOST_STATIC_ASSERT
> -#define BUILD_ASSERT_DECL BOOST_STATIC_ASSERT
> +#define BUILD_ASSERT(EXPR) static_assert(EXPR, "assertion failed")
> +#define BUILD_ASSERT_DECL(EXPR) static_assert(EXPR, "assertion failed")
> #elif (__GNUC__ * 256 + __GNUC_MINOR__ >= 0x403 \
> || __has_extension(c_static_assert))
> #define BUILD_ASSERT_DECL(EXPR) _Static_assert(EXPR, #EXPR)
> diff --git a/m4/ax_cxx_compile_stdcxx.m4 b/m4/ax_cxx_compile_stdcxx.m4
> new file mode 100644
> index 000000000000..5032bba8091d
> --- /dev/null
> +++ b/m4/ax_cxx_compile_stdcxx.m4
> @@ -0,0 +1,982 @@
> +# ===========================================================================
> +# https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
> +# ===========================================================================
> +#
> +# SYNOPSIS
> +#
> +# AX_CXX_COMPILE_STDCXX(VERSION, [ext|noext], [mandatory|optional])
> +#
> +# DESCRIPTION
> +#
> +# Check for baseline language coverage in the compiler for the specified
> +# version of the C++ standard. If necessary, add switches to CXX and
> +# CXXCPP to enable support. VERSION may be '11' (for the C++11 standard)
> +# or '14' (for the C++14 standard).
> +#
> +# The second argument, if specified, indicates whether you insist on an
> +# extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
> +# -std=c++11). If neither is specified, you get whatever works, with
> +# preference for an extended mode.
> +#
> +# The third argument, if specified 'mandatory' or if left unspecified,
> +# indicates that baseline support for the specified C++ standard is
> +# required and that the macro should error out if no mode with that
> +# support is found. If specified 'optional', then configuration proceeds
> +# regardless, after defining HAVE_CXX${VERSION} if and only if a
> +# supporting mode is found.
> +#
> +# LICENSE
> +#
> +# Copyright (c) 2008 Benjamin Kosnik <bkoz at redhat.com>
> +# Copyright (c) 2012 Zack Weinberg <zackw at panix.com>
> +# Copyright (c) 2013 Roy Stogner <roystgnr at ices.utexas.edu>
> +# Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov at google.com>
> +# Copyright (c) 2015 Paul Norman <penorman at mac.com>
> +# Copyright (c) 2015 Moritz Klammler <moritz at klammler.eu>
> +# Copyright (c) 2016 Krzesimir Nowak <qdlacz at gmail.com>
> +#
> +# Copying and distribution of this file, with or without modification, are
> +# permitted in any medium without royalty provided the copyright notice
> +# and this notice are preserved. This file is offered as-is, without any
> +# warranty.
> +
> +#serial 7
> +
> +dnl This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
> +dnl (serial version number 13).
> +
> +AX_REQUIRE_DEFINED([AC_MSG_WARN])
> +AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
> + m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
> + [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
> + [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
> + [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
> + m4_if([$2], [], [],
> + [$2], [ext], [],
> + [$2], [noext], [],
> + [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX])])dnl
> + m4_if([$3], [], [ax_cxx_compile_cxx$1_required=true],
> + [$3], [mandatory], [ax_cxx_compile_cxx$1_required=true],
> + [$3], [optional], [ax_cxx_compile_cxx$1_required=false],
> + [m4_fatal([invalid third argument `$3' to AX_CXX_COMPILE_STDCXX])])
> + AC_LANG_PUSH([C++])dnl
> + ac_success=no
> + AC_CACHE_CHECK(whether $CXX supports C++$1 features by default,
> + ax_cv_cxx_compile_cxx$1,
> + [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
> + [ax_cv_cxx_compile_cxx$1=yes],
> + [ax_cv_cxx_compile_cxx$1=no])])
> + if test x$ax_cv_cxx_compile_cxx$1 = xyes; then
> + ac_success=yes
> + fi
> +
> + m4_if([$2], [noext], [], [dnl
> + if test x$ac_success = xno; then
> + for alternative in ${ax_cxx_compile_alternatives}; do
> + switch="-std=gnu++${alternative}"
> + cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
> + AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
> + $cachevar,
> + [ac_save_CXX="$CXX"
> + CXX="$CXX $switch"
> + AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
> + [eval $cachevar=yes],
> + [eval $cachevar=no])
> + CXX="$ac_save_CXX"])
> + if eval test x\$$cachevar = xyes; then
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> + ac_success=yes
> + break
> + fi
> + done
> + fi])
> +
> + m4_if([$2], [ext], [], [dnl
> + if test x$ac_success = xno; then
> + dnl HP's aCC needs +std=c++11 according to:
> + dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
> + dnl Cray's crayCC needs "-h std=c++11"
> + for alternative in ${ax_cxx_compile_alternatives}; do
> + for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
> + cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
> + AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
> + $cachevar,
> + [ac_save_CXX="$CXX"
> + CXX="$CXX $switch"
> + AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
> + [eval $cachevar=yes],
> + [eval $cachevar=no])
> + CXX="$ac_save_CXX"])
> + if eval test x\$$cachevar = xyes; then
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> + ac_success=yes
> + break
> + fi
> + done
> + if test x$ac_success = xyes; then
> + break
> + fi
> + done
> + fi])
> + AC_LANG_POP([C++])
> + if test x$ax_cxx_compile_cxx$1_required = xtrue; then
> + if test x$ac_success = xno; then
> + AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
> + fi
> + fi
> + if test x$ac_success = xno; then
> + HAVE_CXX$1=0
> + AC_MSG_NOTICE([No compiler with C++$1 support was found])
> + else
> + HAVE_CXX$1=1
> + AC_DEFINE(HAVE_CXX$1,1,
> + [define if the compiler supports basic C++$1 syntax])
> + fi
> + AC_SUBST(HAVE_CXX$1)
> + m4_if([$1], [17], [AC_MSG_WARN([C++17 is not yet standardized, so the checks may change in incompatible ways anytime])])
> +])
> +
> +
> +dnl Test body for checking C++11 support
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
> +)
> +
> +
> +dnl Test body for checking C++14 support
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
> +)
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
> + _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
> +)
> +
> +dnl Tests for new features in C++11
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[
> +
> +// If the compiler admits that it is not ready for C++11, why torture it?
> +// Hopefully, this will speed up the test.
> +
> +#ifndef __cplusplus
> +
> +#error "This is not a C++ compiler"
> +
> +#elif __cplusplus < 201103L
> +
> +#error "This is not a C++11 compiler"
> +
> +#else
> +
> +namespace cxx11
> +{
> +
> + namespace test_static_assert
> + {
> +
> + template <typename T>
> + struct check
> + {
> + static_assert(sizeof(int) <= sizeof(T), "not big enough");
> + };
> +
> + }
> +
> + namespace test_final_override
> + {
> +
> + struct Base
> + {
> + virtual void f() {}
> + };
> +
> + struct Derived : public Base
> + {
> + virtual void f() override {}
> + };
> +
> + }
> +
> + namespace test_double_right_angle_brackets
> + {
> +
> + template < typename T >
> + struct check {};
> +
> + typedef check<void> single_type;
> + typedef check<check<void>> double_type;
> + typedef check<check<check<void>>> triple_type;
> + typedef check<check<check<check<void>>>> quadruple_type;
> +
> + }
> +
> + namespace test_decltype
> + {
> +
> + int
> + f()
> + {
> + int a = 1;
> + decltype(a) b = 2;
> + return a + b;
> + }
> +
> + }
> +
> + namespace test_type_deduction
> + {
> +
> + template < typename T1, typename T2 >
> + struct is_same
> + {
> + static const bool value = false;
> + };
> +
> + template < typename T >
> + struct is_same<T, T>
> + {
> + static const bool value = true;
> + };
> +
> + template < typename T1, typename T2 >
> + auto
> + add(T1 a1, T2 a2) -> decltype(a1 + a2)
> + {
> + return a1 + a2;
> + }
> +
> + int
> + test(const int c, volatile int v)
> + {
> + static_assert(is_same<int, decltype(0)>::value == true, "");
> + static_assert(is_same<int, decltype(c)>::value == false, "");
> + static_assert(is_same<int, decltype(v)>::value == false, "");
> + auto ac = c;
> + auto av = v;
> + auto sumi = ac + av + 'x';
> + auto sumf = ac + av + 1.0;
> + static_assert(is_same<int, decltype(ac)>::value == true, "");
> + static_assert(is_same<int, decltype(av)>::value == true, "");
> + static_assert(is_same<int, decltype(sumi)>::value == true, "");
> + static_assert(is_same<int, decltype(sumf)>::value == false, "");
> + static_assert(is_same<int, decltype(add(c, v))>::value == true, "");
> + return (sumf > 0.0) ? sumi : add(c, v);
> + }
> +
> + }
> +
> + namespace test_noexcept
> + {
> +
> + int f() { return 0; }
> + int g() noexcept { return 0; }
> +
> + static_assert(noexcept(f()) == false, "");
> + static_assert(noexcept(g()) == true, "");
> +
> + }
> +
> + namespace test_constexpr
> + {
> +
> + template < typename CharT >
> + unsigned long constexpr
> + strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
> + {
> + return *s ? strlen_c_r(s + 1, acc + 1) : acc;
> + }
> +
> + template < typename CharT >
> + unsigned long constexpr
> + strlen_c(const CharT *const s) noexcept
> + {
> + return strlen_c_r(s, 0UL);
> + }
> +
> + static_assert(strlen_c("") == 0UL, "");
> + static_assert(strlen_c("1") == 1UL, "");
> + static_assert(strlen_c("example") == 7UL, "");
> + static_assert(strlen_c("another\0example") == 7UL, "");
> +
> + }
> +
> + namespace test_rvalue_references
> + {
> +
> + template < int N >
> + struct answer
> + {
> + static constexpr int value = N;
> + };
> +
> + answer<1> f(int&) { return answer<1>(); }
> + answer<2> f(const int&) { return answer<2>(); }
> + answer<3> f(int&&) { return answer<3>(); }
> +
> + void
> + test()
> + {
> + int i = 0;
> + const int c = 0;
> + static_assert(decltype(f(i))::value == 1, "");
> + static_assert(decltype(f(c))::value == 2, "");
> + static_assert(decltype(f(0))::value == 3, "");
> + }
> +
> + }
> +
> + namespace test_uniform_initialization
> + {
> +
> + struct test
> + {
> + static const int zero {};
> + static const int one {1};
> + };
> +
> + static_assert(test::zero == 0, "");
> + static_assert(test::one == 1, "");
> +
> + }
> +
> + namespace test_lambdas
> + {
> +
> + void
> + test1()
> + {
> + auto lambda1 = [](){};
> + auto lambda2 = lambda1;
> + lambda1();
> + lambda2();
> + }
> +
> + int
> + test2()
> + {
> + auto a = [](int i, int j){ return i + j; }(1, 2);
> + auto b = []() -> int { return '0'; }();
> + auto c = [=](){ return a + b; }();
> + auto d = [&](){ return c; }();
> + auto e = [a, &b](int x) mutable {
> + const auto identity = [](int y){ return y; };
> + for (auto i = 0; i < a; ++i)
> + a += b--;
> + return x + identity(a + b);
> + }(0);
> + return a + b + c + d + e;
> + }
> +
> + int
> + test3()
> + {
> + const auto nullary = [](){ return 0; };
> + const auto unary = [](int x){ return x; };
> + using nullary_t = decltype(nullary);
> + using unary_t = decltype(unary);
> + const auto higher1st = [](nullary_t f){ return f(); };
> + const auto higher2nd = [unary](nullary_t f1){
> + return [unary, f1](unary_t f2){ return f2(unary(f1())); };
> + };
> + return higher1st(nullary) + higher2nd(nullary)(unary);
> + }
> +
> + }
> +
> + namespace test_variadic_templates
> + {
> +
> + template <int...>
> + struct sum;
> +
> + template <int N0, int... N1toN>
> + struct sum<N0, N1toN...>
> + {
> + static constexpr auto value = N0 + sum<N1toN...>::value;
> + };
> +
> + template <>
> + struct sum<>
> + {
> + static constexpr auto value = 0;
> + };
> +
> + static_assert(sum<>::value == 0, "");
> + static_assert(sum<1>::value == 1, "");
> + static_assert(sum<23>::value == 23, "");
> + static_assert(sum<1, 2>::value == 3, "");
> + static_assert(sum<5, 5, 11>::value == 21, "");
> + static_assert(sum<2, 3, 5, 7, 11, 13>::value == 41, "");
> +
> + }
> +
> + // http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
> + // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function
> + // because of this.
> + namespace test_template_alias_sfinae
> + {
> +
> + struct foo {};
> +
> + template<typename T>
> + using member = typename T::member_type;
> +
> + template<typename T>
> + void func(...) {}
> +
> + template<typename T>
> + void func(member<T>*) {}
> +
> + void test();
> +
> + void test() { func<foo>(0); }
> +
> + }
> +
> +} // namespace cxx11
> +
> +#endif // __cplusplus >= 201103L
> +
> +]])
> +
> +
> +dnl Tests for new features in C++14
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[
> +
> +// If the compiler admits that it is not ready for C++14, why torture it?
> +// Hopefully, this will speed up the test.
> +
> +#ifndef __cplusplus
> +
> +#error "This is not a C++ compiler"
> +
> +#elif __cplusplus < 201402L
> +
> +#error "This is not a C++14 compiler"
> +
> +#else
> +
> +namespace cxx14
> +{
> +
> + namespace test_polymorphic_lambdas
> + {
> +
> + int
> + test()
> + {
> + const auto lambda = [](auto&&... args){
> + const auto istiny = [](auto x){
> + return (sizeof(x) == 1UL) ? 1 : 0;
> + };
> + const int aretiny[] = { istiny(args)... };
> + return aretiny[0];
> + };
> + return lambda(1, 1L, 1.0f, '1');
> + }
> +
> + }
> +
> + namespace test_binary_literals
> + {
> +
> + constexpr auto ivii = 0b0000000000101010;
> + static_assert(ivii == 42, "wrong value");
> +
> + }
> +
> + namespace test_generalized_constexpr
> + {
> +
> + template < typename CharT >
> + constexpr unsigned long
> + strlen_c(const CharT *const s) noexcept
> + {
> + auto length = 0UL;
> + for (auto p = s; *p; ++p)
> + ++length;
> + return length;
> + }
> +
> + static_assert(strlen_c("") == 0UL, "");
> + static_assert(strlen_c("x") == 1UL, "");
> + static_assert(strlen_c("test") == 4UL, "");
> + static_assert(strlen_c("another\0test") == 7UL, "");
> +
> + }
> +
> + namespace test_lambda_init_capture
> + {
> +
> + int
> + test()
> + {
> + auto x = 0;
> + const auto lambda1 = [a = x](int b){ return a + b; };
> + const auto lambda2 = [a = lambda1(x)](){ return a; };
> + return lambda2();
> + }
> +
> + }
> +
> + namespace test_digit_separators
> + {
> +
> + constexpr auto ten_million = 100'000'000;
> + static_assert(ten_million == 100000000, "");
> +
> + }
> +
> + namespace test_return_type_deduction
> + {
> +
> + auto f(int& x) { return x; }
> + decltype(auto) g(int& x) { return x; }
> +
> + template < typename T1, typename T2 >
> + struct is_same
> + {
> + static constexpr auto value = false;
> + };
> +
> + template < typename T >
> + struct is_same<T, T>
> + {
> + static constexpr auto value = true;
> + };
> +
> + int
> + test()
> + {
> + auto x = 0;
> + static_assert(is_same<int, decltype(f(x))>::value, "");
> + static_assert(is_same<int&, decltype(g(x))>::value, "");
> + return x;
> + }
> +
> + }
> +
> +} // namespace cxx14
> +
> +#endif // __cplusplus >= 201402L
> +
> +]])
> +
> +
> +dnl Tests for new features in C++17
> +
> +m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[
> +
> +// If the compiler admits that it is not ready for C++17, why torture it?
> +// Hopefully, this will speed up the test.
> +
> +#ifndef __cplusplus
> +
> +#error "This is not a C++ compiler"
> +
> +#elif __cplusplus <= 201402L
> +
> +#error "This is not a C++17 compiler"
> +
> +#else
> +
> +#if defined(__clang__)
> + #define REALLY_CLANG
> +#else
> + #if defined(__GNUC__)
> + #define REALLY_GCC
> + #endif
> +#endif
> +
> +#include <initializer_list>
> +#include <utility>
> +#include <type_traits>
> +
> +namespace cxx17
> +{
> +
> +#if !defined(REALLY_CLANG)
> + namespace test_constexpr_lambdas
> + {
> +
> + // TODO: test it with clang++ from git
> +
> + constexpr int foo = [](){return 42;}();
> +
> + }
> +#endif // !defined(REALLY_CLANG)
> +
> + namespace test::nested_namespace::definitions
> + {
> +
> + }
> +
> + namespace test_fold_expression
> + {
> +
> + template<typename... Args>
> + int multiply(Args... args)
> + {
> + return (args * ... * 1);
> + }
> +
> + template<typename... Args>
> + bool all(Args... args)
> + {
> + return (args && ...);
> + }
> +
> + }
> +
> + namespace test_extended_static_assert
> + {
> +
> + static_assert (true);
> +
> + }
> +
> + namespace test_auto_brace_init_list
> + {
> +
> + auto foo = {5};
> + auto bar {5};
> +
> + static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
> + static_assert(std::is_same<int, decltype(bar)>::value);
> + }
> +
> + namespace test_typename_in_template_template_parameter
> + {
> +
> + template<template<typename> typename X> struct D;
> +
> + }
> +
> + namespace test_fallthrough_nodiscard_maybe_unused_attributes
> + {
> +
> + int f1()
> + {
> + return 42;
> + }
> +
> + [[nodiscard]] int f2()
> + {
> + [[maybe_unused]] auto unused = f1();
> +
> + switch (f1())
> + {
> + case 17:
> + f1();
> + [[fallthrough]];
> + case 42:
> + f1();
> + }
> + return f1();
> + }
> +
> + }
> +
> + namespace test_extended_aggregate_initialization
> + {
> +
> + struct base1
> + {
> + int b1, b2 = 42;
> + };
> +
> + struct base2
> + {
> + base2() {
> + b3 = 42;
> + }
> + int b3;
> + };
> +
> + struct derived : base1, base2
> + {
> + int d;
> + };
> +
> + derived d1 {{1, 2}, {}, 4}; // full initialization
> + derived d2 {{}, {}, 4}; // value-initialized bases
> +
> + }
> +
> + namespace test_general_range_based_for_loop
> + {
> +
> + struct iter
> + {
> + int i;
> +
> + int& operator* ()
> + {
> + return i;
> + }
> +
> + const int& operator* () const
> + {
> + return i;
> + }
> +
> + iter& operator++()
> + {
> + ++i;
> + return *this;
> + }
> + };
> +
> + struct sentinel
> + {
> + int i;
> + };
> +
> + bool operator== (const iter& i, const sentinel& s)
> + {
> + return i.i == s.i;
> + }
> +
> + bool operator!= (const iter& i, const sentinel& s)
> + {
> + return !(i == s);
> + }
> +
> + struct range
> + {
> + iter begin() const
> + {
> + return {0};
> + }
> +
> + sentinel end() const
> + {
> + return {5};
> + }
> + };
> +
> + void f()
> + {
> + range r {};
> +
> + for (auto i : r)
> + {
> + [[maybe_unused]] auto v = i;
> + }
> + }
> +
> + }
> +
> + namespace test_lambda_capture_asterisk_this_by_value
> + {
> +
> + struct t
> + {
> + int i;
> + int foo()
> + {
> + return [*this]()
> + {
> + return i;
> + }();
> + }
> + };
> +
> + }
> +
> + namespace test_enum_class_construction
> + {
> +
> + enum class byte : unsigned char
> + {};
> +
> + byte foo {42};
> +
> + }
> +
> + namespace test_constexpr_if
> + {
> +
> + template <bool cond>
> + int f ()
> + {
> + if constexpr(cond)
> + {
> + return 13;
> + }
> + else
> + {
> + return 42;
> + }
> + }
> +
> + }
> +
> + namespace test_selection_statement_with_initializer
> + {
> +
> + int f()
> + {
> + return 13;
> + }
> +
> + int f2()
> + {
> + if (auto i = f(); i > 0)
> + {
> + return 3;
> + }
> +
> + switch (auto i = f(); i + 4)
> + {
> + case 17:
> + return 2;
> +
> + default:
> + return 1;
> + }
> + }
> +
> + }
> +
> +#if !defined(REALLY_CLANG)
> + namespace test_template_argument_deduction_for_class_templates
> + {
> +
> + // TODO: test it with clang++ from git
> +
> + template <typename T1, typename T2>
> + struct pair
> + {
> + pair (T1 p1, T2 p2)
> + : m1 {p1},
> + m2 {p2}
> + {}
> +
> + T1 m1;
> + T2 m2;
> + };
> +
> + void f()
> + {
> + [[maybe_unused]] auto p = pair{13, 42u};
> + }
> +
> + }
> +#endif // !defined(REALLY_CLANG)
> +
> + namespace test_non_type_auto_template_parameters
> + {
> +
> + template <auto n>
> + struct B
> + {};
> +
> + B<5> b1;
> + B<'a'> b2;
> +
> + }
> +
> +#if !defined(REALLY_CLANG)
> + namespace test_structured_bindings
> + {
> +
> + // TODO: test it with clang++ from git
> +
> + int arr[2] = { 1, 2 };
> + std::pair<int, int> pr = { 1, 2 };
> +
> + auto f1() -> int(&)[2]
> + {
> + return arr;
> + }
> +
> + auto f2() -> std::pair<int, int>&
> + {
> + return pr;
> + }
> +
> + struct S
> + {
> + int x1 : 2;
> + volatile double y1;
> + };
> +
> + S f3()
> + {
> + return {};
> + }
> +
> + auto [ x1, y1 ] = f1();
> + auto& [ xr1, yr1 ] = f1();
> + auto [ x2, y2 ] = f2();
> + auto& [ xr2, yr2 ] = f2();
> + const auto [ x3, y3 ] = f3();
> +
> + }
> +#endif // !defined(REALLY_CLANG)
> +
> +#if !defined(REALLY_CLANG)
> + namespace test_exception_spec_type_system
> + {
> +
> + // TODO: test it with clang++ from git
> +
> + struct Good {};
> + struct Bad {};
> +
> + void g1() noexcept;
> + void g2();
> +
> + template<typename T>
> + Bad
> + f(T*, T*);
> +
> + template<typename T1, typename T2>
> + Good
> + f(T1*, T2*);
> +
> + static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);
> +
> + }
> +#endif // !defined(REALLY_CLANG)
> +
> + namespace test_inline_variables
> + {
> +
> + template<class T> void f(T)
> + {}
> +
> + template<class T> inline T g(T)
> + {
> + return T{};
> + }
> +
> + template<> inline void f<>(int)
> + {}
> +
> + template<> int g<>(int)
> + {
> + return 5;
> + }
> +
> + }
> +
> +} // namespace cxx17
> +
> +#endif // __cplusplus <= 201402L
> +
> +]])
> diff --git a/m4/openvswitch.m4 b/m4/openvswitch.m4
> index 648750ab5ad9..00ffad35f6b0 100644
> --- a/m4/openvswitch.m4
> +++ b/m4/openvswitch.m4
> @@ -620,3 +620,19 @@ AC_DEFUN([OVS_LIBTOOL_VERSIONS],
> AC_MSG_RESULT([libX-$OVS_MAJOR.$OVS_MINOR.so.$LT_CURRENT.0.$OVS_MICRO)])
> AC_SUBST(OVS_LTINFO)
> ])
> +
> +dnl OVS does not use C++ itself, but it provides public header files
> +dnl that a C++ compiler should accept, so when --enable-Werror is in
> +dnl effect and a C++ compiler is available, we enable building a C++
> +dnl source file that #includes all the public headers, as a way to
> +dnl ensure that they are acceptable as C++.
> +AC_DEFUN([OVS_CHECK_CXX],
> + [AC_REQUIRE([AC_PROG_CXX])
> + AC_REQUIRE([OVS_ENABLE_WERROR])
> + AX_CXX_COMPILE_STDCXX([11], [], [optional])
> + if test $enable_Werror = yes && test $HAVE_CXX11 = 1; then
> + enable_cxx=:
> + else
> + enable_cxx=false
> + fi
> + AM_CONDITIONAL([HAVE_CXX], [$enable_cxx])])
> --
> 2.10.2
--
Russell Bryant
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