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Jonathan WakelyandTomasz Kamiński
ea37298b65
C++26 changes assert into a variadic macro to support using
assignment-expressions that would be interpreted as multiple macro
arguments, in particular one containing:
* template parameter lists: func<int, float>()
* calls to overloaded operator[] that accepts multiple arguments: arr[1, 2]
this is C++23 feature, see libstdc++ PR/119855 [1]
* lambdas with explicit captures: [x, y] { ... }
The new expansion in form:
(__VA_ARGS__) ? void (1 ? 1 : bool (__VA_ARGS__))
: __assert_fail (...)
Has the following properties:
* Use of (__VA_ARGS__) ? ... : ..., requires that __VA_ARGS__
is contextually convertible to bool. This means that enumerators
of scoped enumeration are no longer accepted (they are only
explicitly convertible). Thus this patch address the glibc PR/27276 [2].
* Nested ternary 1 ? 1 : bool (__VA_ARGS__) guarantees that
expression expanded from __VA_ARGS__ is not evaluated twice.
This is used instead of unevaluated context (like sizeof...)
to support C++ expressions that are not allowed in unevaluated
context (lambdas until C++20, co_await, co_yield).
* bool (__VA_ARGS__) is ill-formed if __VA_ARGS__ expands to
multiple arguments: assert(1, 2)
* bool (__VA_ARGS__) also triggers warnings when __VA_ARGS__
expands to x = 1: assert(x = 1)
To guarantee that the code snippets from assert/test-assert-c++-variadic.cc,
are actually checked for validity, we need to compile this test in C++26
(-std=c++26) mode. To achieve that, this patch compiles the file with
test-config-cxxflags-stdcxx26 variable as additional flag, that is set to
-std=c++26 if $(TEST_CXX) executable supports that flag, and empty otherwise.
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119855
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=27276
Co-authored-by: Tomasz Kamiński <tkaminsk@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
116 lines
2.1 KiB
C++
116 lines
2.1 KiB
C++
/* Test assert as a variadic macro for C++ code snippets.
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Copyright The GNU Toolchain Authors.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This test requires C++26, and is compiled with -std=c++26
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if GCC version supports that, and no additional options
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otherwise. */
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#if defined __cplusplus && __cplusplus > 202302L
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#undef NDEBUG
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#include <assert.h>
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template <typename T1, typename T2>
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bool
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foo ()
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{ return true; }
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struct C
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{
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C (int p, int r) : x (p + r) {}
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int x;
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};
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int
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func ()
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{
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return 1;
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}
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static void
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test_enabled ()
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{
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{
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assert (foo <int, float> ());
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}
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{
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assert (C {1, 2}.x > 0);
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}
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{
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int x = 10, y = 20;
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assert ([x, y] { return x < y; } ());
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}
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{
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/* Ill-formed, not an assigment expression. */
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// assert (func (), func ());
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assert ((func (), func ()));
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}
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}
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template <typename Ts>
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constexpr bool
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assert_works ()
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{
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return requires (Ts ts) {
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assert (ts);
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};
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}
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enum OE { oe };
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enum TE : int { te };
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enum class SE : int { se };
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static_assert ( assert_works <OE> ());
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static_assert ( assert_works <TE> ());
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static_assert (!assert_works <SE> ());
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#define NDEBUG
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#include <assert.h>
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static void
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test_disabled ()
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{
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/* Assert is variadic, but ignores arguments */
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assert(1, 2);
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assert(+, 1, -, 2, *, 30);
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}
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static int
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do_test ()
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{
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test_enabled ();
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test_disabled ();
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return 0;
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}
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#else
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#include <support/test-driver.h>
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static int
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do_test ()
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{
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return EXIT_UNSUPPORTED;
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}
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#endif
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#include <support/test-driver.c>
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