[libc++] Disable incomplete library features.

Adds a new CMake option to disable the usage of incomplete headers.
These incomplete headers are not guaranteed to be ABI stable. This
option is intended to be used by vendors so they can avoid their users
from code that's not ready for production usage.

The option is enabled by default.

Differential Revision: https://reviews.llvm.org/D106763

Author: mordante

libcxx/CMakeLists.txt

@@ -123,6 +123,11 @@ option(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS
    to provide compile-time errors when using features unavailable on some version of
    the shared library they shipped should turn this on and see `include/__availability`
    for more details." OFF)
+option(LIBCXX_ENABLE_INCOMPLETE_FEATURES
+    "Whether to enable support for incomplete library features. Incomplete features
+    are new library features under development. These features don't guarantee
+    ABI stability nor the quality of completed library features. Vendors
+    shipping the library may want to disable this option." ON)
 set(LIBCXX_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/configs/legacy.cfg.in" CACHE STRING
     "The Lit testing configuration to use when running the tests.")
 set(LIBCXX_TEST_PARAMS "" CACHE STRING
@@ -883,6 +888,10 @@ config_define_if_not(LIBCXX_ENABLE_FILESYSTEM _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY)
 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_VENDOR_AVAILABILITY_ANNOTATIONS _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
+# Incomplete features get their own specific disabling flags. This makes it
+# easier to grep for target specific flags once the feature is complete.
+config_define_if_not(LIBCXX_ENABLE_INCOMPLETE_FEATURES _LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+config_define_if_not(LIBCXX_ENABLE_INCOMPLETE_FEATURES _LIBCPP_HAS_NO_INCOMPLETE_RANGES)
 
 if (LIBCXX_ABI_DEFINES)
   set(abi_defines)

libcxx/cmake/caches/Apple.cmake

@@ -11,6 +11,7 @@ set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
 set(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT ON CACHE BOOL "")
 set(LIBCXX_ENABLE_DEBUG_MODE_SUPPORT OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS ON CACHE BOOL "")
+set(LIBCXX_ENABLE_INCOMPLETE_FEATURES OFF CACHE BOOL "")
 
 set(LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
 set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")

libcxx/docs/BuildingLibcxx.rst

@@ -251,6 +251,15 @@ libc++ specific options
    This option can be used to enable or disable the filesystem components on
    platforms that may not support them. For example on Windows.
 
+.. option:: LIBCXX_ENABLE_INCOMPLETE_FEATURES:BOOL
+
+  **Default**: ``ON``
+
+  Whether to enable support for incomplete library features. Incomplete features
+  are new library features under development. These features don't guarantee
+  ABI stability nor the quality of completed library features. Vendors
+  shipping the library may want to disable this option.
+
 .. option:: LIBCXX_INSTALL_LIBRARY_DIR:PATH
 
   **Default**: ``lib${LIBCXX_LIBDIR_SUFFIX}``

libcxx/include/__config_site.in

@@ -34,6 +34,8 @@
 #cmakedefine _LIBCPP_HAS_PARALLEL_ALGORITHMS
 #cmakedefine _LIBCPP_HAS_NO_RANDOM_DEVICE
 #cmakedefine _LIBCPP_HAS_NO_LOCALIZATION
+#cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_FORMAT
+#cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_RANGES
 
 @_LIBCPP_ABI_DEFINES@
 

libcxx/include/format

@@ -60,6 +60,10 @@ namespace std {
 #include <__format/format_parse_context.h>
 #include <version>
 
+#if defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+# error "The Format library is not supported since libc++ has been configured with LIBCXX_ENABLE_INCOMPLETE_FEATURES disabled"
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

libcxx/include/ranges

@@ -183,6 +183,10 @@ namespace std::ranges {
 #include <type_traits>
 #include <version>
 
+#if defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+# error "The Ranges library is not supported since libc++ has been configured with LIBCXX_ENABLE_INCOMPLETE_FEATURES disabled"
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif

libcxx/src/CMakeLists.txt

@@ -12,7 +12,6 @@ set(LIBCXX_SOURCES
   condition_variable.cpp
   condition_variable_destructor.cpp
   exception.cpp
-  format.cpp
   functional.cpp
   future.cpp
   hash.cpp
@@ -74,6 +73,12 @@ if (LIBCXX_ENABLE_LOCALIZATION)
     )
 endif()
 
+if(LIBCXX_ENABLE_INCOMPLETE_FEATURES)
+  list(APPEND LIBCXX_SOURCES
+    format.cpp
+  )
+endif()
+
 if(WIN32)
   list(APPEND LIBCXX_SOURCES
     support/win32/locale_win32.cpp

libcxx/test/libcxx/double_include.sh.cpp

@@ -91,7 +91,9 @@
 #    include <filesystem>
 #endif
 #include <float.h>
-#include <format>
+#ifndef _LIBCPP_HAS_NO_INCOMPLETE_FORMAT
+#    include <format>
+#endif
 #include <forward_list>
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
 #    include <fstream>
@@ -143,7 +145,9 @@
 #endif
 #include <queue>
 #include <random>
-#include <ranges>
+#ifndef _LIBCPP_HAS_NO_INCOMPLETE_RANGES
+#    include <ranges>
+#endif
 #include <ratio>
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
 #    include <regex>

libcxx/test/libcxx/inclusions/ranges.inclusions.compile.pass.cpp

@@ -12,6 +12,7 @@
 // clang-format off
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
 
 // <ranges>
 

libcxx/test/libcxx/min_max_macros.compile.pass.cpp

@@ -136,8 +136,10 @@ TEST_MACROS();
 #endif
 #include <float.h>
 TEST_MACROS();
-#include <format>
+#ifndef _LIBCPP_HAS_NO_INCOMPLETE_FORMAT
+#    include <format>
 TEST_MACROS();
+#endif
 #include <forward_list>
 TEST_MACROS();
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
@@ -218,8 +220,10 @@ TEST_MACROS();
 TEST_MACROS();
 #include <random>
 TEST_MACROS();
-#include <ranges>
+#ifndef _LIBCPP_HAS_NO_INCOMPLETE_RANGES
+#    include <ranges>
 TEST_MACROS();
+#endif
 #include <ratio>
 TEST_MACROS();
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION