[libc++] Include <__config_site> from <__config>

Prior to this patch, we would generate a fancy <__config> header by
concatenating <__config_site> and <__config>. This complexifies the
build system and also increases the difference between what's tested
and what's actually installed.

This patch removes that complexity and instead simply installs <__config_site>
alongside the libc++ headers. <__config_site> is then included by <__config>,
which is much simpler. Doing this also opens the door to having different
<__config_site> headers depending on the target, which was impossible before.

It does change the workflow for testing header-only changes to libc++.
Previously, we would run `lit` against the headers in libcxx/include.
After this patch, we run it against a fake installation root of the
headers (containing a proper <__config_site> header). This makes use
closer to testing what we actually install, which is good, however it
does mean that we have to update that root before testing header changes.
Thus, we now need to run `ninja check-cxx-deps` before running `lit` by
hand.

Differential Revision: https://reviews.llvm.org/D97572

libcxx/CMakeLists.txt

@@ -403,21 +403,23 @@ endif ()
 # Configure System
 #===============================================================================
 
+# TODO: Projects that depend on libc++ should use LIBCXX_GENERATED_INCLUDE_DIR
+# instead of hard-coding include/c++/v1.
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE}/c++)
-  set(LIBCXX_HEADER_DIR ${LLVM_BINARY_DIR})
+  set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE}/c++)
   if(LIBCXX_LIBDIR_SUBDIR)
     string(APPEND LIBCXX_LIBRARY_DIR /${LIBCXX_LIBDIR_SUBDIR})
     string(APPEND LIBCXX_INSTALL_LIBRARY_DIR /${LIBCXX_LIBDIR_SUBDIR})
   endif()
 elseif(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
-  set(LIBCXX_HEADER_DIR  ${LLVM_BINARY_DIR})
+  set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
 else()
   set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})
-  set(LIBCXX_HEADER_DIR  ${CMAKE_BINARY_DIR})
+  set(LIBCXX_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
 endif()
 

libcxx/benchmarks/CMakeLists.txt

@@ -10,7 +10,7 @@ set(CMAKE_FOLDER "${CMAKE_FOLDER}/Benchmarks")
 set(BENCHMARK_LIBCXX_COMPILE_FLAGS
     -Wno-unused-command-line-argument
     -nostdinc++
-    -isystem ${LIBCXX_SOURCE_DIR}/include
+    -isystem "${LIBCXX_GENERATED_INCLUDE_DIR}"
     -L${LIBCXX_LIBRARY_DIR}
     -Wl,-rpath,${LIBCXX_LIBRARY_DIR}
     ${SANITIZER_FLAGS}
@@ -20,7 +20,6 @@ if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
           -L${LIBCXX_CXX_ABI_LIBRARY_PATH}
           -Wl,-rpath,${LIBCXX_CXX_ABI_LIBRARY_PATH})
 endif()
-list(APPEND BENCHMARK_LIBCXX_COMPILE_FLAGS -include "${LIBCXX_BINARY_DIR}/__config_site")
 split_list(BENCHMARK_LIBCXX_COMPILE_FLAGS)
 
 ExternalProject_Add(google-benchmark-libcxx

libcxx/cmake/Modules/HandleLibCXXABI.cmake

@@ -52,14 +52,14 @@ macro(setup_abi_lib abidefines abishared abistatic abifiles abidirs)
             COMMENT "Copying C++ ABI header ${fpath}...")
         list(APPEND abilib_headers "${dst}")
 
-        if (LIBCXX_HEADER_DIR)
-          set(dst "${LIBCXX_HEADER_DIR}/include/c++/v1/${dstdir}/${fpath}")
-          add_custom_command(OUTPUT ${dst}
-              DEPENDS ${src}
-              COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
-              COMMENT "Copying C++ ABI header ${fpath}...")
-          list(APPEND abilib_headers "${dst}")
-        endif()
+        # TODO: libc++ shouldn't be responsible for copying the libc++abi
+        # headers into the right location.
+        set(dst "${LIBCXX_GENERATED_INCLUDE_DIR}/include/c++/v1/${dstdir}/${fpath}")
+        add_custom_command(OUTPUT ${dst}
+            DEPENDS ${src}
+            COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+            COMMENT "Copying C++ ABI header ${fpath}...")
+        list(APPEND abilib_headers "${dst}")
 
         if (LIBCXX_INSTALL_HEADERS)
           install(FILES "${LIBCXX_BINARY_INCLUDE_DIR}/${fpath}"

libcxx/docs/TestingLibcxx.rst

@@ -37,6 +37,12 @@ whether the required libraries have been built, you can use the
   $ <build>/bin/llvm-lit -sv libcxx/test/std/depr/depr.c.headers/stdlib_h.pass.cpp # Run a single test
   $ <build>/bin/llvm-lit -sv libcxx/test/std/atomics libcxx/test/std/threads # Test std::thread and std::atomic
 
+In the default configuration, the tests are built against headers that form a
+fake installation root of libc++. This installation root has to be updated when
+changes are made to the headers, so you should re-run the `cxx-test-depends`
+target before running the tests manually with `lit` when you make any sort of
+change, including to the headers.
+
 Sometimes you'll want to change the way LIT is running the tests. Custom options
 can be specified using the `--param=<name>=<val>` flag. The most common option
 you'll want to change is the standard dialect (ie -std=c++XX). By default the

libcxx/include/CMakeLists.txt

@@ -4,6 +4,7 @@ set(files
   __bits
   __bsd_locale_defaults.h
   __bsd_locale_fallbacks.h
+  __config
   __debug
   __errc
   __functional_03
@@ -190,65 +191,28 @@ set(files
   wctype.h
   )
 
-configure_file("__config_site.in"
-               "${LIBCXX_BINARY_DIR}/__config_site"
-               @ONLY)
+configure_file("__config_site.in" "${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site" @ONLY)
 
-# Generate a custom __config header. The new header is created
-# by prepending __config_site to the current __config header.
-add_custom_command(OUTPUT ${LIBCXX_BINARY_DIR}/__generated_config
-  COMMAND ${Python3_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/cat_files.py
-    ${LIBCXX_BINARY_DIR}/__config_site
-    ${LIBCXX_SOURCE_DIR}/include/__config
-    -o ${LIBCXX_BINARY_DIR}/__generated_config
-  DEPENDS ${LIBCXX_SOURCE_DIR}/include/__config
-          ${LIBCXX_BINARY_DIR}/__config_site
-)
-# Add a target that executes the generation commands.
-add_custom_target(cxx-generated-config ALL
-  DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
-
-if(LIBCXX_HEADER_DIR)
-  set(output_dir ${LIBCXX_HEADER_DIR}/include/c++/v1)
-
-  set(out_files)
-  foreach(f ${files})
-    set(src ${CMAKE_CURRENT_SOURCE_DIR}/${f})
-    set(dst ${output_dir}/${f})
-    add_custom_command(OUTPUT ${dst}
-      DEPENDS ${src}
-      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
-      COMMENT "Copying CXX header ${f}")
-    list(APPEND out_files ${dst})
-  endforeach()
-
-  # Copy the generated header as __config into build directory.
-  set(src ${LIBCXX_BINARY_DIR}/__generated_config)
-  set(dst ${output_dir}/__config)
+set(_all_includes "${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site")
+foreach(f ${files})
+  set(src "${CMAKE_CURRENT_SOURCE_DIR}/${f}")
+  set(dst "${LIBCXX_GENERATED_INCLUDE_DIR}/${f}")
   add_custom_command(OUTPUT ${dst}
-      DEPENDS ${src} cxx-generated-config
-      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
-      COMMENT "Copying CXX __config")
-  list(APPEND out_files ${dst})
-  add_custom_target(generate-cxx-headers ALL DEPENDS ${out_files})
+    DEPENDS ${src}
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+    COMMENT "Copying CXX header ${f}")
+  list(APPEND _all_includes "${dst}")
+endforeach()
 
-  add_library(cxx-headers INTERFACE)
-  add_dependencies(cxx-headers generate-cxx-headers ${LIBCXX_CXX_ABI_HEADER_TARGET})
-  # TODO: Use target_include_directories once we figure out why that breaks the runtimes build
-  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
-    target_compile_options(cxx-headers INTERFACE /I "${output_dir}")
-  else()
-    target_compile_options(cxx-headers INTERFACE -I "${output_dir}")
-  endif()
+add_custom_target(generate-cxx-headers DEPENDS ${_all_includes})
 
-  # Make sure the generated __config_site header is included when we build the library.
-  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
-    target_compile_options(cxx-headers INTERFACE /FI "${LIBCXX_BINARY_DIR}/__config_site")
-  else()
-    target_compile_options(cxx-headers INTERFACE -include "${LIBCXX_BINARY_DIR}/__config_site")
-  endif()
+add_library(cxx-headers INTERFACE)
+add_dependencies(cxx-headers generate-cxx-headers ${LIBCXX_CXX_ABI_HEADER_TARGET})
+# TODO: Use target_include_directories once we figure out why that breaks the runtimes build
+if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
+  target_compile_options(cxx-headers INTERFACE /I "${LIBCXX_GENERATED_INCLUDE_DIR}")
 else()
-  add_library(cxx-headers INTERFACE)
+  target_compile_options(cxx-headers INTERFACE -I "${LIBCXX_GENERATED_INCLUDE_DIR}")
 endif()
 
 if (LIBCXX_INSTALL_HEADERS)
@@ -261,16 +225,15 @@ if (LIBCXX_INSTALL_HEADERS)
     )
   endforeach()
 
-  # Install the generated header as __config.
-  install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
+  # Install the generated __config_site.
+  install(FILES ${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site
     DESTINATION ${LIBCXX_INSTALL_HEADER_PREFIX}include/c++/v1
     PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-    RENAME __config
     COMPONENT cxx-headers)
 
   if (NOT CMAKE_CONFIGURATION_TYPES)
     add_custom_target(install-cxx-headers
-                      DEPENDS cxx-headers cxx-generated-config
+                      DEPENDS cxx-headers
                       COMMAND "${CMAKE_COMMAND}"
                               -DCMAKE_INSTALL_COMPONENT=cxx-headers
                               -P "${CMAKE_BINARY_DIR}/cmake_install.cmake")

libcxx/include/__config

@@ -10,6 +10,8 @@
 #ifndef _LIBCPP_CONFIG
 #define _LIBCPP_CONFIG
 
+#include <__config_site>
+
 #if defined(_MSC_VER) && !defined(__clang__)
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    define _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER

libcxx/test/configs/legacy.cfg.in

@@ -3,6 +3,7 @@
 import os
 import site
 
+config.cxx_headers              = "@LIBCXX_GENERATED_INCLUDE_DIR@"
 config.cxx_under_test           = "@CMAKE_CXX_COMPILER@"
 config.project_obj_root         = "@CMAKE_BINARY_DIR@"
 config.libcxx_src_root          = "@LIBCXX_SOURCE_DIR@"

libcxx/utils/ci/run-buildbot

@@ -399,9 +399,12 @@ legacy-standalone)
           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
           -DLLVM_PATH="${MONOREPO_ROOT}/llvm" \
           -DLIBCXXABI_LIBCXX_PATH="${MONOREPO_ROOT}/libcxx" \
-          -DLIBCXXABI_LIBCXX_INCLUDES="${MONOREPO_ROOT}/libcxx/include" \
+          -DLIBCXXABI_LIBCXX_INCLUDES="${BUILD_DIR}/libcxx/include/c++/v1" \
           -DLIBCXXABI_LIBCXX_LIBRARY_PATH="${BUILD_DIR}/libcxx/lib"
 
+    echo "+++ Generating libc++ headers"
+    ${NINJA} -vC "${BUILD_DIR}/libcxx" generate-cxx-headers
+
     echo "+++ Building libc++abi"
     ${NINJA} -vC "${BUILD_DIR}/libcxxabi" cxxabi
 

libcxx/utils/libcxx/test/config.py

@@ -334,7 +334,6 @@ def configure_default_compile_flags(self):
 
     def configure_compile_flags_header_includes(self):
         support_path = os.path.join(self.libcxx_src_root, 'test', 'support')
-        self.configure_config_site_header()
         if self.cxx_stdlib_under_test != 'libstdc++' and \
            not self.target_info.is_windows() and \
            not self.target_info.is_zos():
@@ -352,33 +351,19 @@ def configure_compile_flags_header_includes(self):
                                          'set_windows_crt_report_mode.h')
             ]
         cxx_headers = self.get_lit_conf('cxx_headers')
-        if cxx_headers == '' or (cxx_headers is None
-                                 and self.cxx_stdlib_under_test != 'libc++'):
+        if cxx_headers is None and self.cxx_stdlib_under_test != 'libc++':
             self.lit_config.note('using the system cxx headers')
             return
         self.cxx.compile_flags += ['-nostdinc++']
-        if cxx_headers is None:
-            cxx_headers = os.path.join(self.libcxx_src_root, 'include')
         if not os.path.isdir(cxx_headers):
-            self.lit_config.fatal("cxx_headers='%s' is not a directory."
-                                  % cxx_headers)
+            self.lit_config.fatal("cxx_headers='{}' is not a directory.".format(cxx_headers))
         self.cxx.compile_flags += ['-I' + cxx_headers]
         if self.libcxx_obj_root is not None:
             cxxabi_headers = os.path.join(self.libcxx_obj_root, 'include',
                                           'c++build')
             if os.path.isdir(cxxabi_headers):
                 self.cxx.compile_flags += ['-I' + cxxabi_headers]
 
-    def configure_config_site_header(self):
-        # Check for a possible __config_site in the build directory. We
-        # use this if it exists.
-        if self.libcxx_obj_root is None:
-            return
-        config_site_header = os.path.join(self.libcxx_obj_root, '__config_site')
-        if not os.path.isfile(config_site_header):
-            return
-        self.cxx.compile_flags += ['-include', config_site_header]
-
     def configure_link_flags(self):
         # Configure library path
         self.configure_link_flags_cxx_library_path()

libcxxabi/test/libcxxabi/test/config.py

@@ -60,7 +60,6 @@ def configure_compile_flags(self):
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
-        self.configure_config_site_header()
         cxx_headers = self.get_lit_conf('cxx_headers', None) or \
             os.path.join(self.libcxxabi_hdr_root, 'include', 'c++', 'v1')
         if cxx_headers == '':

libunwind/test/libunwind/test/config.py

@@ -52,8 +52,6 @@ def configure_compile_flags(self):
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
-        self.configure_config_site_header()
-
         libunwind_headers = self.get_lit_conf(
             'libunwind_headers',
             os.path.join(self.libunwind_src_root, 'include'))