[RFC][libc++] Install modules.

The patch is based on the discussion in SG-15 on 12.12.2023.

Fixes: #73089

libcxx/CMakeLists.txt

@@ -178,6 +178,10 @@ set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
 option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
+cmake_dependent_option(LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCES
+  "Install the libc++ C++20 module interface unit source files (experimental)." OFF
+  "LIBCXX_ENABLE_STD_MODULES" OFF
+)
 cmake_dependent_option(LIBCXX_INSTALL_STATIC_LIBRARY
   "Install the static libc++ library." ON
   "LIBCXX_ENABLE_STATIC;LIBCXX_INSTALL_LIBRARY" OFF)
@@ -425,6 +429,8 @@ set(LIBCXX_INSTALL_INCLUDE_DIR "${CMAKE_INSTALL_INCLUDEDIR}/c++/v1" CACHE STRING
     "Path where target-agnostic libc++ headers should be installed.")
 set(LIBCXX_INSTALL_RUNTIME_DIR "${CMAKE_INSTALL_BINDIR}" CACHE STRING
     "Path where built libc++ runtime libraries should be installed.")
+set(LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCE_DIR "share/libc++/v1" CACHE STRING
+    "Path where target-agnostic libc++ module interface unit source should be installed.")
 
 set(LIBCXX_SHARED_OUTPUT_NAME "c++" CACHE STRING "Output name for the shared libc++ runtime library.")
 set(LIBCXX_STATIC_OUTPUT_NAME "c++" CACHE STRING "Output name for the static libc++ runtime library.")

libcxx/cmake/caches/Generic-cxx26.cmake

@@ -1,2 +1,3 @@
+set(LIBCXX_INSTALL_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 +1,2 @@
+set(LIBCXX_INSTALL_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_HARDENING_MODE "extensive" CACHE STRING "")

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

@@ -1,2 +1,3 @@
+set(LIBCXX_INSTALL_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

@@ -1,2 +1,3 @@
+set(LIBCXX_INSTALL_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 +1,2 @@
+set(LIBCXX_INSTALL_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 +1,2 @@
+set(LIBCXX_INSTALL_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 +1,2 @@
+set(LIBCXX_INSTALL_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

@@ -1,3 +1,4 @@
+set(LIBCXX_INSTALL_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-unicode.cmake

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

libcxx/docs/Modules.rst

@@ -69,7 +69,6 @@ Some of the current limitations
  * The path to the compiler may not be a symlink, ``clang-scan-deps`` does
    not handle that case properly
  * Libc++ is not tested with modules instead of headers
- * The module ``.cppm`` files are not installed
  * Clang supports modules using GNU extensions, but libc++ does not work using
    GNU extensions.
  * Clang:

libcxx/docs/ReleaseNotes/18.rst

@@ -93,6 +93,13 @@ Improvements and New Features
   infrastructure no longer depends on a modern CMake, it works with the minimal
   required LLVM version (3.20.0).
 
+- The ``.cppm`` files of experimental standard library modules can now be
+  installed. By default, they are not installed. This can be enabled by
+  configuring CMake with ``-DLIBCXX_INSTALL_MODULES=ON``. The installation
+  directory can be configured with the CMake option
+  ``-DLIBCXX_INSTALL_MODULE_DIR=<path>``. The default location is
+  ``share/libc++/v1`` in the same prefix as the ``include`` directory.
+
 
 Deprecations and Removals
 -------------------------

libcxx/modules/CMakeLists.txt

@@ -182,3 +182,56 @@ add_custom_target(generate-cxx-modules
   ALL DEPENDS
     ${_all_modules}
 )
+
+# Use the relative path between the installation and the module in the json
+# file. This allows moving the entire installation to a different location.
+file(RELATIVE_PATH LIBCXX_MODULE_RELATIVE_PATH
+  ${CMAKE_INSTALL_PREFIX}/${LIBCXX_INSTALL_LIBRARY_DIR}
+  ${CMAKE_INSTALL_PREFIX}/${LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCE_DIR})
+configure_file(
+  "modules.json.in"
+  "${LIBCXX_LIBRARY_DIR}/libc++.modules.json"
+  @ONLY
+)
+
+# Dummy library to make modules an installation component.
+add_library(cxx-modules INTERFACE)
+add_dependencies(cxx-modules generate-cxx-modules)
+
+if (LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCES)
+  foreach(file ${LIBCXX_MODULE_STD_SOURCES} ${LIBCXX_MODULE_STD_COMPAT_SOURCES})
+    get_filename_component(dir ${file} DIRECTORY)
+    install(FILES ${file}
+      DESTINATION "${LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCE_DIR}/${dir}"
+      COMPONENT cxx-modules
+      PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+    )
+  endforeach()
+
+  # Install the generated module files.
+  install(FILES
+      "${LIBCXX_GENERATED_MODULE_DIR}/std.cppm"
+      "${LIBCXX_GENERATED_MODULE_DIR}/std.compat.cppm"
+    DESTINATION "${LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCE_DIR}"
+    COMPONENT cxx-modules
+    PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+  )
+
+  # Install the module manifest.
+  install(FILES
+      "${LIBCXX_LIBRARY_DIR}/libc++.modules.json"
+    DESTINATION "${LIBCXX_INSTALL_LIBRARY_DIR}"
+    COMPONENT cxx-modules
+    PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+  )
+
+  if (NOT CMAKE_CONFIGURATION_TYPES)
+    add_custom_target(install-cxx-modules
+                      DEPENDS cxx-modules
+                      COMMAND "${CMAKE_COMMAND}"
+                              -DCMAKE_INSTALL_COMPONENT=cxx-modules
+                              -P "${CMAKE_BINARY_DIR}/cmake_install.cmake")
+    # Stripping is a no-op for modules
+    add_custom_target(install-cxx-modules-stripped DEPENDS install-cxx-headers)
+  endif()
+endif()

libcxx/modules/modules.json.in

@@ -0,0 +1,26 @@
+{
+  "version": 1,
+  "revision": 1,
+  "modules": [
+    {
+      "logical-name": "std",
+      "source-path": "@LIBCXX_MODULE_RELATIVE_PATH@/std.cppm",
+      "is-standard-library": true,
+      "local-arguments": {
+        "system-include-directories": [
+          "@LIBCXX_MODULE_RELATIVE_PATH@"
+        ]
+      }
+    },
+    {
+      "logical-name": "std.compat",
+      "source-path": "@LIBCXX_MODULE_RELATIVE_PATH@/std.compat.cppm",
+      "is-std-library": true,
+      "local-arguments": {
+        "system-include-directories": [
+          "@LIBCXX_MODULE_RELATIVE_PATH@"
+        ]
+      }
+    }
+  ]
+}

libcxx/src/CMakeLists.txt

@@ -399,6 +399,9 @@ if (NOT CMAKE_CONFIGURATION_TYPES)
     if(LIBCXX_INSTALL_HEADERS)
       set(header_install_target install-cxx-headers)
     endif()
+    if(LIBCXX_INSTALL_MODULE_INTERFACE_UNIT_SOURCES)
+      set(header_install_target install-cxx-modules)
+    endif()
     add_custom_target(install-cxx
                       DEPENDS ${lib_install_target}
                               cxx_experimental