[libc++] Re-add transitive includes that had been removed since LLVM 14

This commit re-adds transitive includes that had been removed by
4cd04d1, c36870c, a83f4b9, 1458458, 2e2f315,
and 489637e. This should cover almost all the includes that had
been removed since LLVM 14 and that would contribute to breaking user
code when releasing LLVM 15.

It is possible to disable the inclusion of these headers by defining
_LIBCPP_REMOVE_TRANSITIVE_INCLUDES. The intent is that vendors will
enable that macro and start fixing downstream issues immediately. We
can then remove the macro (and the transitive includes) by default in
a future release. That way, we will break users only once by removing
transitive includes in bulk instead of doing it bit by bit a every
release, which is more disruptive for users.

Note 1: The set of headers to re-add was found by re-generating the
        transitive include test on a checkout of release/14.x, which
        provided the list of all transitive includes we used to provide.

Note 2: Several includes of <vector>, <optional>, <array> and <unordered_map>
        have been added in this commit. These transitive inclusions were
        added when we implemented boyer_moore_searcher in <functional>.

Note 3: This is a best effort patch to try and resolve downstream breakage
        caused since branching LLVM 14. I wasn't able to perfectly mirror
        transitive includes in LLVM 14 for a few headers, so I added a
        release note explaining it. To summarize, adding boyer_moore_searcher
        created a bunch of circular dependencies, so we have to break
        backwards compatibility in a few cases.

Differential Revision: https://reviews.llvm.org/D128661

Author: ldionne

libcxx/cmake/caches/Generic-no-transitive-includes.cmake

@@ -0,0 +1,2 @@
+set(LIBCXX_TEST_PARAMS "enable_transitive_includes=False" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/docs/ReleaseNotes.rst

@@ -97,19 +97,15 @@ API Changes
   ``<filesystem>`` header. The associated macro
   ``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed.
 
-- Some libc++ headers no longer transitively include all of:
-    - ``<algorithm>``
-    - ``<chrono>``
-    - ``<exception>``
-    - ``<functional>``
-    - ``<iterator>``
-    - ``<new>``
-    - ``<typeinfo>``
-    - ``<utility>``
-
-  If, after updating libc++, you see compiler errors related to missing declarations
-  in namespace ``std``, it might be because one of your source files now needs to
-  include one or more of the headers listed above.
+- Libc++ is getting ready to remove unnecessary transitive inclusions. This may
+  break your code in the future. To future-proof your code to these removals,
+  please compile your code with ``_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`` defined
+  and fix any compilation error resulting from missing includes.
+
+- The ``<algorithm>``, ``<array>``, ``<optional>``, ``<unordered_map>`` and ``<vector>``
+  headers no longer transitively include the ``<functional>`` header. If you see compiler
+  errors related to missing declarations in namespace ``std``, make sure you have the
+  necessary includes.
 
 - The integer distributions ``binomial_distribution``, ``discrete_distribution``,
   ``geometric_distribution``, ``negative_binomial_distribution``, ``poisson_distribution``,

libcxx/include/algorithm

@@ -1260,6 +1260,12 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/unwrap_iter.h>
 #include <__algorithm/upper_bound.h>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <chrono>
+#  include <iterator>
+#  include <utility>
+#endif
+
 // standard-mandated includes
 #include <initializer_list>
 

libcxx/include/any

@@ -94,6 +94,10 @@ namespace std {
 #include <typeinfo>
 #include <version>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <chrono>
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

libcxx/include/array

@@ -123,6 +123,12 @@ template <size_t I, class T, size_t N> const T&& get(const array<T, N>&&) noexce
 #include <type_traits>
 #include <version>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <algorithm>
+#  include <iterator>
+#  include <utility>
+#endif
+
 // standard-mandated includes
 
 // [iterator.range]

libcxx/include/atomic

@@ -534,6 +534,10 @@ template <class T>
 # include <__threading_support>
 #endif
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <chrono>
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

libcxx/include/bit

@@ -71,6 +71,10 @@ namespace std {
 #include <type_traits>
 #include <version>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <iosfwd>
+#endif
+
 #if defined(__IBMCPP__)
 #  include "__support/ibm/support.h"
 #endif

libcxx/include/charconv

@@ -96,6 +96,10 @@ namespace std {
 #include <limits>
 #include <type_traits>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <iosfwd>
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

libcxx/include/coroutine

@@ -46,6 +46,10 @@ struct suspend_always;
 #include <__coroutine/trivial_awaitables.h>
 #include <version>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <iosfwd>
+#endif
+
 // standard-mandated includes
 #include <compare>
 

libcxx/include/deque

@@ -185,6 +185,12 @@ template <class T, class Allocator, class Predicate>
 #include <type_traits>
 #include <version>
 
+#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
+#  include <algorithm>
+#  include <functional>
+#  include <iterator>
+#endif
+
 // standard-mandated includes
 
 // [iterator.range]