Revert "Revert llvm#76246 and llvm#76083"

This reverts commit 5c150e7.

Author: mysterymath

.github/workflows/libcxx-build-and-test.yaml

@@ -35,7 +35,6 @@ concurrency:
 
 
 env:
-  CMAKE: "/opt/bin/cmake"
   # LLVM POST-BRANCH bump version
   # LLVM POST-BRANCH add compiler test for ToT - 1, e.g. "Clang 17"
   # LLVM RELEASE bump remove compiler ToT - 3, e.g. "Clang 15"
@@ -169,24 +168,18 @@ jobs:
           'bootstrapping-build'
         ]
         machine: [ 'libcxx-runners-8-set' ]
-        std_modules: [ 'OFF' ]
         include:
         - config: 'generic-cxx26'
           machine: libcxx-runners-8-set
-          std_modules: 'ON'
         - config: 'generic-asan'
           machine: libcxx-runners-8-set
-          std_modules: 'OFF'
         - config: 'generic-tsan'
           machine: libcxx-runners-8-set
-          std_modules: 'OFF'
         - config: 'generic-ubsan'
           machine: libcxx-runners-8-set
-          std_modules: 'OFF'
         # Use a larger machine for MSAN to avoid timeout and memory allocation issues.
         - config: 'generic-msan'
           machine: libcxx-runners-8-set
-          std_modules: 'OFF'
     runs-on: ${{ matrix.machine }}
     steps:
       - uses: actions/checkout@v4
@@ -196,7 +189,6 @@ jobs:
           CC: clang-18
           CXX: clang++-18
           ENABLE_CLANG_TIDY: "OFF"
-          ENABLE_STD_MODULES: ${{ matrix.std_modules }}
       - uses: actions/upload-artifact@v3
         if: always()
         with:

libcxx/CMakeLists.txt

@@ -124,12 +124,6 @@ option(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS
    the shared library they shipped should turn this on and see `include/__availability`
    for more details." OFF)
 option(LIBCXX_ENABLE_CLANG_TIDY "Whether to compile and run clang-tidy checks" OFF)
-# TODO MODULES Remove this option and test for the requirements (CMake/Clang) instead.
-option(LIBCXX_ENABLE_STD_MODULES
-   "Whether to enable the building the C++23 `std` module. This feature is
-    experimental and has additional dependencies. Only enable this when
-    interested in testing or developing this module. See
-    https://libcxx.llvm.org/Modules.html for more information." OFF)
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
@@ -779,7 +773,6 @@ config_define_if_not(LIBCXX_ENABLE_RANDOM_DEVICE _LIBCPP_HAS_NO_RANDOM_DEVICE)
 config_define_if_not(LIBCXX_ENABLE_LOCALIZATION _LIBCPP_HAS_NO_LOCALIZATION)
 config_define_if_not(LIBCXX_ENABLE_UNICODE _LIBCPP_HAS_NO_UNICODE)
 config_define_if_not(LIBCXX_ENABLE_WIDE_CHARACTERS _LIBCPP_HAS_NO_WIDE_CHARACTERS)
-config_define_if_not(LIBCXX_ENABLE_STD_MODULES _LIBCPP_HAS_NO_STD_MODULES)
 config_define_if_not(LIBCXX_ENABLE_TIME_ZONE_DATABASE _LIBCPP_HAS_NO_TIME_ZONE_DATABASE)
 config_define_if_not(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
 
@@ -863,19 +856,15 @@ endfunction()
 add_subdirectory(include)
 add_subdirectory(src)
 add_subdirectory(utils)
-if (LIBCXX_ENABLE_STD_MODULES)
-  add_subdirectory(modules)
-endif()
+add_subdirectory(modules)
 
 set(LIBCXX_TEST_DEPS "cxx_experimental")
 
 if (LIBCXX_ENABLE_CLANG_TIDY)
   list(APPEND LIBCXX_TEST_DEPS cxx-tidy)
 endif()
 
-if (LIBCXX_ENABLE_STD_MODULES)
-  list(APPEND LIBCXX_TEST_DEPS generate-cxx-modules generate-test-module-std)
-endif()
+list(APPEND LIBCXX_TEST_DEPS generate-cxx-modules)
 
 if (LIBCXX_INCLUDE_BENCHMARKS)
   add_subdirectory(benchmarks)

libcxx/cmake/caches/Generic-cxx26.cmake

@@ -1,3 +1,2 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_TEST_PARAMS "std=c++26" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/cmake/caches/Generic-hardening-mode-extensive.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_HARDENING_MODE "extensive" CACHE STRING "")

libcxx/cmake/caches/Generic-no-exceptions.cmake

@@ -1,3 +1,2 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-experimental.cmake

@@ -1,3 +1,2 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_TEST_PARAMS "enable_experimental=False" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/cmake/caches/Generic-no-filesystem.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-localization.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_LOCALIZATION OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-random_device.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-threads.cmake

@@ -1,4 +1,3 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_THREADS OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-tzdb.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_TIME_ZONE_DATABASE OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-unicode.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_UNICODE OFF CACHE BOOL "")

libcxx/cmake/caches/Generic-no-wide-characters.cmake

@@ -1,2 +1 @@
-set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_WIDE_CHARACTERS OFF CACHE BOOL "")

libcxx/docs/Modules.rst

@@ -115,7 +115,7 @@ directory. First libc++ needs to be build with module support enabled.
   $ git clone https://github.com/llvm/llvm-project.git
   $ cd llvm-project
   $ mkdir build
-  $ cmake -G Ninja -S runtimes -B build -DLIBCXX_ENABLE_STD_MODULES=ON -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"
+  $ cmake -G Ninja -S runtimes -B build -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"
   $ ninja -C build
 
 The above ``build`` directory will be referred to as ``<build>`` in the

libcxx/docs/ReleaseNotes/18.rst

@@ -89,6 +89,10 @@ Improvements and New Features
 - The ``_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE`` macro has been added to make
   the function ``std::shared_ptr<...>::unique()`` available.
 
+- The cmake option ``LIBCXX_ENABLE_STD_MODULES`` has been removed. The test
+  infrastructure no longer depends on a modern CMake, it works with the minimal
+  required LLVM version (3.20.0).
+
 
 Deprecations and Removals
 -------------------------

libcxx/docs/TestingLibcxx.rst

@@ -394,7 +394,7 @@ Custom Directives
 ~~~~~~~~~~~~~~~~~
 
 Lit has many directives built in (e.g., ``DEFINE``, ``UNSUPPORTED``). In addition to those directives, libc++ adds two additional libc++-specific directives that makes
-writing tests easier. See `libc++-specific Lit Directives`_ for more information about the ``FILE_DEPENDENCIES`` and ``ADDITIONAL_COMPILE_FLAGS`` libc++-specific directives.
+writing tests easier. See `libc++-specific Lit Directives`_ for more information about the ``FILE_DEPENDENCIES``, ``ADDITIONAL_COMPILE_FLAGS``, and ``MODULE_DEPENDENCIES`` libc++-specific directives.
 
 .. _libc++-specific Lit Directives:
 .. list-table:: libc++-specific Lit Directives
@@ -417,6 +417,13 @@ writing tests easier. See `libc++-specific Lit Directives`_ for more information
      - The additional compiler flags specified by a space-separated list to the ``ADDITIONAL_COMPILE_FLAGS`` libc++-specific Lit directive will be added to the end of the ``%{compile_flags}``
        substitution for the test that contains it. This libc++-specific Lit directive makes it possible to add special compilation flags without having to resort to writing a ``.sh.cpp`` test (see
        `Lit Meaning of libc++ Test Filenames`_), more powerful but perhaps overkill.
+   * - ``MODULE_DEPENDENCIES``
+     - ``// MODULE_DEPENDENCIES: std std.compat``
+     - This directive will build the required C++23 standard library
+       modules and add the additional compiler flags in
+       %{compile_flags}. (Libc++ offers these modules in C++20 as an
+       extension.)
+
 
 Benchmarks
 ==========

libcxx/modules/CMakeLists.txt

@@ -1,8 +1,3 @@
-if (CMAKE_VERSION VERSION_LESS 3.26)
-  message(WARNING "The libc++ modules won't be available because the CMake version is too old. Update to CMake 3.26 or later.")
-  return()
-endif()
-
 # The headers of Table 24: C++ library headers [tab:headers.cpp]
 # and the headers of Table 25: C++ headers for C library facilities [tab:headers.cpp.c]
 set(LIBCXX_MODULE_STD_SOURCES
@@ -142,28 +137,6 @@ set(LIBCXX_MODULE_STD_COMPAT_SOURCES
   std.compat/cwctype.inc
 )
 
-# TODO MODULES the CMakeLists.txt in the install directory is only temporary
-# When that is removed the configured file can use the substitution
-# LIBCXX_GENERATED_INCLUDE_TARGET_DIR avoiding this set.
-# Also clean up the parts needed to generate the install version.
-# - LIBCXX_GENERATED_INCLUDE_DIR contains the libc++ headers
-# - LIBCXX_GENERATED_INCLUDE_TARGET_DIR contains the libc++ site config
-if ("${LIBCXX_GENERATED_INCLUDE_DIR}" STREQUAL "${LIBCXX_GENERATED_INCLUDE_TARGET_DIR}")
-  # This typically happens when the target is not installed.
-  set(LIBCXX_CONFIGURED_INCLUDE_DIRS "${LIBCXX_GENERATED_INCLUDE_DIR}")
-else()
-  # It's important that the arch directory be included first so that its header files
-  # which interpose on the default include dir be included instead of the default ones.
-  set(LIBCXX_CONFIGURED_INCLUDE_DIRS
-    "${LIBCXX_GENERATED_INCLUDE_TARGET_DIR};${LIBCXX_GENERATED_INCLUDE_DIR}"
-  )
-endif()
-configure_file(
-  "CMakeLists.txt.in"
-  "${LIBCXX_GENERATED_MODULE_DIR}/CMakeLists.txt"
-  @ONLY
-)
-
 set(LIBCXX_MODULE_STD_INCLUDE_SOURCES)
 foreach(file ${LIBCXX_MODULE_STD_SOURCES})
   set(
@@ -193,7 +166,6 @@ configure_file(
 )
 
 set(_all_modules)
-list(APPEND _all_modules "${LIBCXX_GENERATED_MODULE_DIR}/CMakeLists.txt")
 list(APPEND _all_modules "${LIBCXX_GENERATED_MODULE_DIR}/std.cppm")
 list(APPEND _all_modules "${LIBCXX_GENERATED_MODULE_DIR}/std.compat.cppm")
 foreach(file ${LIBCXX_MODULE_STD_SOURCES} ${LIBCXX_MODULE_STD_COMPAT_SOURCES})

libcxx/modules/CMakeLists.txt.in

@@ -87,31 +87,6 @@ if (LIBCXX_INCLUDE_TESTS)
     ${CMAKE_CURRENT_BINARY_DIR}
     DEPENDS cxx-test-depends)
 
-  if(LIBCXX_ENABLE_STD_MODULES)
-    # Generates the modules used in the test.
-    # Note the test will regenerate this with the proper setting
-    # - the right DCMAKE_CXX_STANDARD
-    # - the right test compilation flags
-    # Since modules depend on these flags there currently is no way to
-    # avoid generating these for the tests. The advantage of the
-    # pre generation is that less build information needs to be shared
-    # in the bridge.
-    add_custom_command(
-        OUTPUT "${CMAKE_BINARY_DIR}/test/__config_module__/CMakeCache.txt"
-        COMMAND
-        ${CMAKE_COMMAND}
-            "-G${CMAKE_GENERATOR}"
-            "-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}"
-            "-B${CMAKE_BINARY_DIR}/test/__config_module__"
-            "-H${LIBCXX_GENERATED_MODULE_DIR}"
-            "-DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}"
-            "-DCMAKE_CXX_STANDARD=23"
-            "-DCMAKE_EXPORT_COMPILE_COMMANDS=ON"
-            )
-  add_custom_target(generate-test-module-std
-      DEPENDS "${CMAKE_BINARY_DIR}/test/__config_module__/CMakeCache.txt"
-      COMMENT "Builds generic module std.")
-  endif()
 endif()
 
 if (LIBCXX_GENERATE_COVERAGE)

libcxx/test/CMakeLists.txt

@@ -31,10 +31,3 @@ config.substitutions.append(('%{target-include}', '@LIBCXX_GENERATED_INCLUDE_TAR
 config.substitutions.append(('%{lib}', '@LIBCXX_LIBRARY_DIR@'))
 config.substitutions.append(('%{module}', '@LIBCXX_GENERATED_MODULE_DIR@'))
 config.substitutions.append(('%{test-tools}', '@LIBCXX_TEST_TOOLS_PATH@'))
-
-# The test needs to manually rebuild the module. The compiler flags used in the
-# test need to be the same as the compiler flags used to generate the module.
-# In the future, when CMake can generated modules this may no longer be
-# necessary.
-# TODO MODULES whether it's possible to remove this substitution.
-config.substitutions.append(('%{cmake}', '@CMAKE_COMMAND@'))

libcxx/test/configs/cmake-bridge.cfg.in

@@ -30,6 +30,7 @@
     "%{test-tools}/clang_tidy_checks/libcxx-tidy.plugin",
     "%{cxx}",
     "%{flags} %{compile_flags}",
+    "std",
 )
 
 

libcxx/test/libcxx/module_std.gen.py

@@ -30,6 +30,7 @@
     "%{test-tools}/clang_tidy_checks/libcxx-tidy.plugin",
     "%{cxx}",
     "%{flags} %{compile_flags}",
+    "std.compat",
 )
 
 

libcxx/test/libcxx/module_std_compat.gen.py

@@ -0,0 +1,14 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Make sure that the compile flags contain no module information.
+
+// MODULE_DEPENDENCIES:
+
+// RUN: echo "%{compile_flags}" | grep -v "std.pcm"
+// RUN: echo "%{compile_flags}" | grep -v "std.compat.pcm"

libcxx/test/libcxx/selftest/modules/no-modules.sh.cpp

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++20
+// UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
+
+// XFAIL: has-no-cxx-module-support
+
+// picolibc does not provide the required timespec_get function, and the
+// "using-if-exists" mechanism apparently did not work here.
+// XFAIL: LIBCXX-PICOLIBC-FIXME
+
+// Make sure that the compile flags contain the expected elements.
+// The tests only look for the expected components and not the exact flags.
+// Otherwise changing the location of the module would break this test.
+
+// MODULE_DEPENDENCIES: std std.compat
+
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std=.*/std.pcm .*/std.pcm"
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std.compat=.*/std.compat.pcm .*/std.compat.pcm"