[libc++] Remove the CI job testing Clang 15 (llvm#66406)

Since LLVM 17 has been branched and is on the verge of being released,
we can drop the CI job that tests against Clang 15. I think the number
of cherry-picks to `release/17.x` will be a lot smaller now, so keeping
a Clang 15 job around for that purpose seems unnecessary.

As a fly-by, this patch also removes some Clang 15 workarounds and test
suite annotations as we usually do. It also removes some slightly older
gcc test suite annotations that were missed.

Author: ldionne

libcxx/docs/index.rst

@@ -116,7 +116,7 @@ velocity, libc++ drops support for older compilers as newer ones are released.
 ============ =============== ========================== =====================
 Compiler     Versions        Restrictions               Support policy
 ============ =============== ========================== =====================
-Clang        15, 16, 17-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
+Clang        16, 17, 18-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
 AppleClang   15                                         latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
 Open XL      17.1 (AIX)                                 latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
 GCC          12              In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_

libcxx/include/__ranges/take_while_view.h

@@ -41,18 +41,6 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
-// The spec uses the unnamed requirement inside the `begin` and `end` member functions:
-//     constexpr auto begin() const
-//       requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>>
-// However, due to a clang-14 and clang-15 bug, the above produces a hard error when `const V` is not a range.
-// The workaround is to create a named concept and use the concept instead.
-// As of take_while_view is implemented, the clang-trunk has already fixed the bug.
-// It is OK to remove the workaround once our CI no longer uses clang-14, clang-15 based compilers,
-// because we don't actually expect a lot of vendors to ship a new libc++ with an old clang.
-template <class _View, class _Pred>
-concept __take_while_const_is_range =
-    range<const _View> && indirect_unary_predicate<const _Pred, iterator_t<const _View>>;
-
 template <view _View, class _Pred>
   requires input_range<_View> && is_object_v<_Pred> && indirect_unary_predicate<const _Pred, iterator_t<_View>>
 class take_while_view : public view_interface<take_while_view<_View, _Pred>> {
@@ -87,7 +75,7 @@ class take_while_view : public view_interface<take_while_view<_View, _Pred>> {
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
-    requires __take_while_const_is_range<_View, _Pred>
+    requires range<const _View> && indirect_unary_predicate<const _Pred, iterator_t<const _View>>
   {
     return ranges::begin(__base_);
   }
@@ -99,7 +87,7 @@ class take_while_view : public view_interface<take_while_view<_View, _Pred>> {
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
-    requires __take_while_const_is_range<_View, _Pred>
+    requires range<const _View> && indirect_unary_predicate<const _Pred, iterator_t<const _View>>
   {
     return __sentinel</*_Const=*/true>(ranges::end(__base_), std::addressof(*__pred_));
   }

libcxx/include/__ranges/to.h

@@ -44,14 +44,13 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
-// TODO(clang-15): in the Standard, it's a `constexpr bool` variable, not a concept, but constexpr variables don't
-// short-circuit properly on Clang 15 (fixed in later versions), so use a concept as a workaround.
 template <class _Container>
-concept __reservable_container = sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) {
-  __c.reserve(__n);
-  { __c.capacity() } -> same_as<decltype(__n)>;
-  { __c.max_size() } -> same_as<decltype(__n)>;
-};
+constexpr bool __reservable_container =
+    sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) {
+      __c.reserve(__n);
+      { __c.capacity() } -> same_as<decltype(__n)>;
+      { __c.max_size() } -> same_as<decltype(__n)>;
+    };
 
 template <class _Container, class _Ref>
 constexpr bool __container_insertable = requires(_Container& __c, _Ref&& __ref) {

libcxx/test/libcxx/experimental/fexperimental-library.compile.pass.cpp

@@ -12,10 +12,6 @@
 // GCC does not support the -fexperimental-library flag
 // UNSUPPORTED: gcc
 
-// Clang on AIX currently pretends that it is Clang 15, even though it is not (as of writing
-// this, LLVM 15 hasn't even been branched yet).
-// UNSUPPORTED: clang-15 && buildhost=aix
-
 // ADDITIONAL_COMPILE_FLAGS: -fexperimental-library
 
 #include <version>

libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp

@@ -12,7 +12,7 @@
 // UNSUPPORTED: c++03
 
 // TODO: Investigate these failures which break the CI.
-// UNSUPPORTED: clang-15, clang-16, clang-17, clang-18
+// UNSUPPORTED: clang-16, clang-17, clang-18
 
 // TODO: Investigate this failure on GCC 13 (in Ubuntu Jammy)
 // UNSUPPORTED: gcc-13

libcxx/test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp

@@ -19,7 +19,7 @@
 
 // XFAIL: sanitizer-new-delete && !hwasan
 
-// It fails with clang-14 or clang-16, but passes with clang-15.
+// TODO: Investigate this failure
 // UNSUPPORTED: ubsan
 
 // GCC doesn't support the aligned-allocation flags.

libcxx/test/std/containers/views/mdspan/mdspan/index_operator.pass.cpp

@@ -38,7 +38,7 @@
 #include "../ConvertibleToIntegral.h"
 #include "CustomTestLayouts.h"
 
-// Clang 15 and 16 do not support argument packs as input to operator []
+// Clang 16 does not support argument packs as input to operator []
 #if defined(__clang_major__) && __clang_major__ < 17
 template <class MDS>
 constexpr auto& access(MDS mds) {

libcxx/test/std/language.support/support.srcloc/general.pass.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// UNSUPPORTED: clang-15
 
 #include <source_location>
 

libcxx/test/std/ranges/range.adaptors/range.filter/iterator/arrow.pass.cpp

@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// This test is hitting Clang bugs with LSV in older versions of Clang.
-// UNSUPPORTED: clang-modules-build && clang-15
-
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
 // constexpr iterator_t<V> operator->() const

libcxx/test/std/thread/futures/futures.task/futures.task.members/ctad.static.compile.pass.cpp

@@ -8,7 +8,6 @@
 
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// XFAIL: clang-15
 
 // checks that CTAD for std::packaged_task works properly with static operator() overloads
 

libcxx/test/std/utilities/expected/expected.expected/swap/free.swap.pass.cpp

@@ -6,8 +6,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// Older Clangs do not support the C++20 feature to constrain destructors
-// XFAIL: clang-15
 
 // friend constexpr void swap(expected& x, expected& y) noexcept(noexcept(x.swap(y)));
 

libcxx/test/std/utilities/expected/expected.void/swap/free.swap.pass.cpp

@@ -6,8 +6,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// Older Clangs do not support the C++20 feature to constrain destructors
-// XFAIL: clang-15
 
 // friend constexpr void swap(expected& x, expected& y) noexcept(noexcept(swap(x,y)));
 

libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/ctad.static.compile.pass.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// XFAIL: clang-15
 
 // checks that CTAD for std::function works properly with static operator() overloads
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_copy.pass.cpp

@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Triggers a Clang assertion: llvm.org/PR45879
-// UNSUPPORTED: clang-15
-
 // <tuple>
 
 // template <class... Types> class tuple;

libcxx/utils/ci/buildkite-pipeline.yml

@@ -271,25 +271,6 @@ steps:
           limit: 2
     timeout_in_minutes: 120
 
-  - label: "Clang 15"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx23"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-15"
-        CXX: "clang++-15"
-        ENABLE_CLANG_TIDY: "On"
-        ENABLE_STD_MODULES: "Off"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
   - label: "Clang 16"
     command: "libcxx/utils/ci/run-buildbot generic-cxx23"
     artifact_paths: