[libc++] Divorce the std Lit feature from the -std=XXX compiler flag

[ldionne]

Summary

After this patch, we can use --param std=c++20 even if the compiler only
supports -std=c++2a. The test suite will handle that for us. The only Lit
feature that isn't fully baked will always be the "in development" one,
since we don't know exactly what year the standard will be ratified in.

This is another take on https://reviews.llvm.org/D99789.

[curdeius]

It's fine with me. I don't mind switching from 2a to 20.

[• Quuxplusone]

libcxx/utils/libcxx/test/params.py

50

if std in fallbacks and
should fix the build errors.

[ldionne]

Fix CI failure - thanks Arthur!

[• Quuxplusone]

This feels simpler than D99789, so OK.
(Somehow wc -l thinks D99789 is simpler, but whatever. This one also updates Generic-cxx20.cmake, which is a good thing.)

[ldionne]

I'll land this once CI is green. Thanks!

libcxx/cmake/caches/Generic-cxx20.cmake

-set(LIBCXX_TEST_PARAMS "std=c++2a" CACHE STRING "")
+set(LIBCXX_TEST_PARAMS "std=c++20" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/docs/TestingLibcxx.rst

.. option:: stdlib=<stdlib name>
   **Values**: libc++, libstdc++, msvc
 
   Specify the C++ standard library being tested. The default is libc++ if this
   option is not provided. This option is intended to allow running the libc++
   test suite against other standard library implementations.
 
 .. option:: std=<standard version>
 
-  **Values**: c++03, c++11, c++14, c++17, c++2a, c++2b
+  **Values**: c++03, c++11, c++14, c++17, c++20, c++2b
 
   Change the standard version used when building the tests.
 
 .. option:: cxx_headers=<path/to/headers>
 
   Specify the c++ standard library headers that are tested. By default the
   headers in the source tree are used.
 

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array11.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
 //
 //===----------------------------------------------------------------------===//
 
 // test sized operator delete[] replacement.
 
 // Note that sized delete operator definitions below are simply ignored
 // when sized deallocation is not supported, e.g., prior to C++14.
 
-// UNSUPPORTED: c++14, c++17, c++2a
+// REQUIRES: c++03 || c++11
 // UNSUPPORTED: sanitizer-new-delete
 
 #include <new>
 #include <cstddef>
 #include <cstdlib>
 #include <cassert>
 
 #include "test_macros.h"

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete11.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
 //
 //===----------------------------------------------------------------------===//
 
 // test sized operator delete replacement.
 
 // Note that sized delete operator definitions below are simply ignored
 // when sized deallocation is not supported, e.g., prior to C++14.
 
-// UNSUPPORTED: c++14, c++17, c++2a
+// REQUIRES: c++03 || c++11
 // UNSUPPORTED: sanitizer-new-delete
 
 #include <new>
 #include <cstddef>
 #include <cstdlib>
 #include <cassert>
 
 #include "test_macros.h"

libcxx/test/std/strings/basic.string/string.contains/contains.char.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
 //   constexpr bool contains(charT x) const noexcept;
 
 #include <string>
 #include <cassert>
 

libcxx/test/std/strings/basic.string/string.contains/contains.ptr.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
 //   constexpr bool contains(const CharT *x) const;
 
 #include <string>
 #include <cassert>
 

libcxx/test/std/strings/basic.string/string.contains/contains.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string>
 
 //   constexpr bool contains(basic_string_view x) const noexcept;
 
 #include <string>
 #include <cassert>
 

libcxx/test/std/strings/string.view/string.view.template/contains.char.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
 //   constexpr bool contains(charT x) const noexcept;
 
 #include <string_view>
 #include <cassert>
 

libcxx/test/std/strings/string.view/string.view.template/contains.ptr.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
 //   constexpr bool contains(const CharT *x) const;
 
 #include <string_view>
 #include <cassert>
 

libcxx/test/std/strings/string.view/string.view.template/contains.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // <string_view>
 
 //   constexpr bool contains(string_view x) const noexcept;
 
 #include <string_view>
 #include <cassert>
 

libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_scoped_enum.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // type_traits
 
 // is_scoped_enum // C++2b
 
 #include <type_traits>
 #include <cstddef> // for std::nullptr_t
 #include "test_macros.h"

libcxx/test/std/utilities/utility/utility.underlying/to_underlying.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // [utility.underlying], to_underlying
 // template <class T>
 //     constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
 
 #include <utility>
 #include <cassert>
 #include <limits>

libcxx/test/std/utilities/utility/utility.underlying/to_underlying.verify.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, c++17, c++2a
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // [utility.underlying], to_underlying
 // template <class T>
 //     constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
 
 #include <utility>
 
 struct S {};
 
 int main(int, char**) {
   std::to_underlying(125); // expected-error {{no matching function for call}}
   std::to_underlying(S{}); // expected-error {{no matching function for call}}
 
   return 0;
 }

libcxx/utils/libcxx/test/params.py

 #===----------------------------------------------------------------------===##
 #
 # 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
 #
 #===----------------------------------------------------------------------===##
 
 from libcxx.test.dsl import *
 
-_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++2a', 'c++2b']
 _warningFlags = [
   '-Werror',
   '-Wall',
   '-Wextra',
   '-Wshadow',
   '-Wundef',
   '-Wno-unused-command-line-argument',
   '-Wno-attributes',
_warningFlags = [
   # expect the test suite to be clean.
   '-Wsign-compare',
   '-Wunused-variable',
   '-Wunused-parameter',
   '-Wunreachable-code',
   '-Wno-unused-local-typedef',
 ]
 
+_allStandards = ['c++03', 'c++11', 'c++14', 'c++17', 'c++20', 'c++2b']
+def getStdFlag(cfg, std):
+  fallbacks = {
+    'c++11': 'c++0x',
+    'c++14': 'c++1y',
+    'c++17': 'c++1z',
+    'c++20': 'c++2a',
+  }
+  if hasCompileFlag(cfg, '-std='+std):
+    return '-std='+std
+  if std in fallbacks and hasCompileFlag(cfg, '-std='+fallbacks[std]):
+    return '-std='+fallbacks[std]
+  return None
+
 DEFAULT_PARAMETERS = [
   # Core parameters of the test suite
   Parameter(name='std', choices=_allStandards, type=str,
             help="The version of the standard to compile the test suite with.",
-            default=lambda cfg: next(s for s in reversed(_allStandards) if hasCompileFlag(cfg, '-std='+s)),
+            default=lambda cfg: next(s for s in reversed(_allStandards) if getStdFlag(cfg, s)),
             actions=lambda std: [
               AddFeature(std),
-              AddCompileFlag('-std={}'.format(std)),
+              AddCompileFlag(lambda cfg: getStdFlag(cfg, std)),
             ]),
 
   Parameter(name='enable_exceptions', choices=[True, False], type=bool, default=True,
             help="Whether to enable exceptions when compiling the test suite.",
             actions=lambda exceptions: [] if exceptions else [
               AddFeature('no-exceptions'),
               AddCompileFlag('-fno-exceptions')
             ]),