[libc++] [test] Eliminate the libcpp-no-if-constexpr feature flag.

[• Quuxplusone]

Summary

At this point, every supported compiler that claims a -std=c++17 mode should also support if constexpr. This was an issue for GCC 5 and GCC 6, but hasn't been an issue since GCC 7. (Our current minimum supported GCC version, IIUC, is GCC 10 or 11.)

[Mordante]

Thanks for looking at this! If the CI's happy, I'm happy.

libcxx/utils/libcxx/test/features.py

39

Incidentally I've been looking at this recently and I think libcpp-no-structured-bindings and no-noexcept-function-type can also be removed. Obviously not intended for this patch.

[ldionne]

There's also an instance of __cpp_if_constexpr in libcxx/test/support/container_debug_tests.h you can remove.

libcxx/utils/libcxx/test/features.py

39

Yup, there's some more cleanup we can do!!

libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test container debugging
 
 #include <map>
 #include <set>

libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-has-no-threads
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test multihtreaded container debugging
 
 #include <cassert>
 #include <cstddef>

libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test container debugging
 
 #include <forward_list>
 #include <list>

libcxx/test/libcxx/debug/containers/db_string.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test container debugging
 
 #include <string>
 #include <vector>

libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test container debugging
 
 #include <unordered_map>
 #include <unordered_set>

libcxx/test/libcxx/debug/db_string_view.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: windows
-// UNSUPPORTED: libcpp-no-if-constexpr
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=1
 // UNSUPPORTED: libcxx-no-debug-mode
 
 // test container debugging
 
 #include <string_view>
 

libcxx/test/support/container_debug_tests.h

 #include "debug_mode_helper.h"
 #include "test_allocator.h"
 
 // These test make use of 'if constexpr'.
 #if TEST_STD_VER <= 14
 #error This header may only be used in C++17 and greater
 #endif
 
-#ifndef __cpp_if_constexpr
-#error These tests require if constexpr
-#endif
-
-
 namespace IteratorDebugChecks {
 
 enum ContainerType {
   CT_None,
   CT_String,
   CT_Vector,
   CT_VectorBool,
   CT_List,

libcxx/utils/libcxx/test/features.py

DEFAULT_FEATURES = [
   Feature(name='diagnose-if-support',
           when=lambda cfg: hasCompileFlag(cfg, '-Wuser-defined-warnings'),
           actions=[AddCompileFlag('-Wuser-defined-warnings')]),
 
   Feature(name='has-fblocks',                   when=lambda cfg: hasCompileFlag(cfg, '-fblocks')),
   Feature(name='-fsized-deallocation',          when=lambda cfg: hasCompileFlag(cfg, '-fsized-deallocation')),
   Feature(name='-faligned-allocation',          when=lambda cfg: hasCompileFlag(cfg, '-faligned-allocation')),
   Feature(name='fdelayed-template-parsing',     when=lambda cfg: hasCompileFlag(cfg, '-fdelayed-template-parsing')),
-  Feature(name='libcpp-no-if-constexpr',        when=lambda cfg: '__cpp_if_constexpr' not in featureTestMacros(cfg)),
   Feature(name='libcpp-no-structured-bindings', when=lambda cfg: '__cpp_structured_bindings' not in featureTestMacros(cfg)),
   Feature(name='libcpp-no-concepts',            when=lambda cfg: featureTestMacros(cfg).get('__cpp_concepts', 0) < 201907),
   Feature(name='has-fobjc-arc',                 when=lambda cfg: hasCompileFlag(cfg, '-xobjective-c++ -fobjc-arc') and
                                                                  sys.platform.lower().strip() == 'darwin'), # TODO: this doesn't handle cross-compiling to Apple platforms.
   Feature(name='objective-c++',                 when=lambda cfg: hasCompileFlag(cfg, '-xobjective-c++ -fobjc-arc')),
   Feature(name='no-noexcept-function-type',     when=lambda cfg: featureTestMacros(cfg).get('__cpp_noexcept_function_type', 0) < 201510),
 
   Feature(name='non-lockfree-atomics',
           when=lambda cfg: sourceBuilds(cfg, """