[libc++] Deprecate and remove `uncaught_exception` #101830

frederick-vs-ja · 2024-08-03T15:09:18Z

Works towards P0619R4/#99985.

std::uncaught_exception was not previously deprecated. This patch deprecates it since C++17 as per N4259. std::uncaught_exceptions is used instead as libc++ unconditionally provides this function.

Escape hatches:

_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION restores std::uncaught_exception.

Drive-by changes:

In Cxx20.rst, says that D.11 is already done. It is done in 578d09c.

Works towards P0619R4. - `std::uncaught_exception` was not previously deprecated. This patch deprecates it since C++17 as per N4259. `std::uncaught_exceptions` is used instead as libc++ unconditionally provides this function. Escape hatches: - `_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION` restores `std::uncaught_exception`. Drive-by changes: - In Cxx20.rst, says that D.11 is already done. It is done in 578d09c.

llvmbot · 2024-08-03T15:09:46Z

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

Works towards P0619R4/#99985.

std::uncaught_exception was not previously deprecated. This patch deprecates it since C++17 as per N4259. std::uncaught_exceptions is used instead as libc++ unconditionally provides this function.

Escape hatches:

_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION restores std::uncaught_exception.

Drive-by changes:

In Cxx20.rst, says that D.11 is already done. It is done in 578d09c.

Full diff: https://github.com/llvm/llvm-project/pull/101830.diff

11 Files Affected:

(modified) libcxx/docs/ReleaseNotes/20.rst (+3)
(modified) libcxx/docs/Status/Cxx17.rst (+1)
(modified) libcxx/docs/Status/Cxx17Papers.csv (+1-1)
(modified) libcxx/docs/Status/Cxx20.rst (+1-1)
(modified) libcxx/docs/UsingLibcxx.rst (+3)
(modified) libcxx/include/__exception/operations.h (+3-1)
(modified) libcxx/include/__ostream/basic_ostream.h (+1-1)
(modified) libcxx/include/exception (+1-1)
(modified) libcxx/modules/std/exception.inc (-1)
(modified) libcxx/src/exception.cpp (+3)
(modified) libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp (+4)

diff --git a/libcxx/docs/ReleaseNotes/20.rst b/libcxx/docs/ReleaseNotes/20.rst
index 960fdd7ce0562..79079df6e061d 100644
--- a/libcxx/docs/ReleaseNotes/20.rst
+++ b/libcxx/docs/ReleaseNotes/20.rst
@@ -44,6 +44,9 @@ Implemented Papers
 Improvements and New Features
 -----------------------------
 
+- The ``_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION`` macro has been added to make ``std::uncaught_exception``
+  available.
+
 - TODO
 
 
diff --git a/libcxx/docs/Status/Cxx17.rst b/libcxx/docs/Status/Cxx17.rst
index 3f1f2071300c8..6bccd4cf854c4 100644
--- a/libcxx/docs/Status/Cxx17.rst
+++ b/libcxx/docs/Status/Cxx17.rst
@@ -40,6 +40,7 @@ Paper Status
 
 .. note::
 
+   .. [#note-N4259] N4259: ``std::uncaught_exception`` is deprecated since version 20.0.
    .. [#note-P0067] P0067: ``std::(to|from)_chars`` for integrals has been available since version 7.0. ``std::to_chars`` for ``float`` and ``double`` since version 14.0 ``std::to_chars`` for ``long double`` uses the implementation for ``double``.
    .. [#note-P0226] P0226: Progress is tracked `here <https://https://libcxx.llvm.org/Status/SpecialMath.html>`_.
    .. [#note-P0607] P0607: The parts of P0607 that are not done are the ``<regex>`` bits.
diff --git a/libcxx/docs/Status/Cxx17Papers.csv b/libcxx/docs/Status/Cxx17Papers.csv
index 232feea985545..afdfa6fd0f4d6 100644
--- a/libcxx/docs/Status/Cxx17Papers.csv
+++ b/libcxx/docs/Status/Cxx17Papers.csv
@@ -4,7 +4,7 @@
 "`N4169 <https://wg21.link/N4169>`__","A proposal to add invoke function template","Urbana","|Complete|","3.7",""
 "`N4190 <https://wg21.link/N4190>`__","Removing auto_ptr, random_shuffle(), And Old <functional> Stuff.","Urbana","|Complete|","15.0",""
 "`N4258 <https://wg21.link/N4258>`__","Cleaning-up noexcept in the Library.","Urbana","|In Progress|","3.7",""
-"`N4259 <https://wg21.link/N4259>`__","Wording for std::uncaught_exceptions","Urbana","|Complete|","3.7",""
+"`N4259 <https://wg21.link/N4259>`__","Wording for std::uncaught_exceptions","Urbana","|Complete| [#note-N4259]_","3.7",""
 "`N4277 <https://wg21.link/N4277>`__","TriviallyCopyable ``reference_wrapper``\ .","Urbana","|Complete|","3.2",""
 "`N4279 <https://wg21.link/N4279>`__","Improved insertion interface for unique-key maps.","Urbana","|Complete|","3.7",""
 "`N4280 <https://wg21.link/N4280>`__","Non-member size() and more","Urbana","|Complete|","3.6",""
diff --git a/libcxx/docs/Status/Cxx20.rst b/libcxx/docs/Status/Cxx20.rst
index b76e30fbb3712..951d8cde18338 100644
--- a/libcxx/docs/Status/Cxx20.rst
+++ b/libcxx/docs/Status/Cxx20.rst
@@ -44,7 +44,7 @@ Paper Status
    .. [#note-P0645] P0645: The paper is implemented but still marked as an incomplete feature
       (the feature-test macro is not set).
    .. [#note-P0966] P0966: It was previously erroneously marked as complete in version 8.0. See `bug 45368 <https://llvm.org/PR45368>`__.
-   .. [#note-P0619] P0619: Only sections D.8, D.9, D.10 and D.13 are implemented. Sections D.4, D.7, D.11, and D.12 remain undone.
+   .. [#note-P0619] P0619: Only sections D.7, D.8, D.9, D.10, D.11 and D.13 are implemented. Sections D.4 and D.12 remain undone.
    .. [#note-P0883.1] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.
    .. [#note-P0883.2] P0883: ``ATOMIC_FLAG_INIT`` was marked deprecated in version 14.0, but was undeprecated with the implementation of LWG3659 in version 15.0.
    .. [#note-P0660] P0660: The paper is implemented but the features are experimental and can be enabled via ``-fexperimental-library``.
diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
index df08875c13bea..cf10fe728fca0 100644
--- a/libcxx/docs/UsingLibcxx.rst
+++ b/libcxx/docs/UsingLibcxx.rst
@@ -215,6 +215,9 @@ C++17 Specific Configuration Macros
 
 C++20 Specific Configuration Macros
 -----------------------------------
+**_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION**:
+  This macro is used to re-enable `uncaught_exception`.
+
 **_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE**:
   This macro is used to re-enable the function
   ``std::shared_ptr<...>::unique()``.
diff --git a/libcxx/include/__exception/operations.h b/libcxx/include/__exception/operations.h
index 0a9c7a7c7f0d8..4a0a697c00e6e 100644
--- a/libcxx/include/__exception/operations.h
+++ b/libcxx/include/__exception/operations.h
@@ -29,7 +29,9 @@ using terminate_handler = void (*)();
 _LIBCPP_EXPORTED_FROM_ABI terminate_handler set_terminate(terminate_handler) _NOEXCEPT;
 _LIBCPP_EXPORTED_FROM_ABI terminate_handler get_terminate() _NOEXCEPT;
 
-_LIBCPP_EXPORTED_FROM_ABI bool uncaught_exception() _NOEXCEPT;
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
+_LIBCPP_EXPORTED_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 bool uncaught_exception() _NOEXCEPT;
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
 _LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
 
 class _LIBCPP_EXPORTED_FROM_ABI exception_ptr;
diff --git a/libcxx/include/__ostream/basic_ostream.h b/libcxx/include/__ostream/basic_ostream.h
index 178359d681567..e0698ccb4842a 100644
--- a/libcxx/include/__ostream/basic_ostream.h
+++ b/libcxx/include/__ostream/basic_ostream.h
@@ -152,7 +152,7 @@ basic_ostream<_CharT, _Traits>::sentry::sentry(basic_ostream<_CharT, _Traits>& _
 
 template <class _CharT, class _Traits>
 basic_ostream<_CharT, _Traits>::sentry::~sentry() {
-  if (__os_.rdbuf() && __os_.good() && (__os_.flags() & ios_base::unitbuf) && !uncaught_exception()) {
+  if (__os_.rdbuf() && __os_.good() && (__os_.flags() & ios_base::unitbuf) && uncaught_exceptions() == 0) {
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
diff --git a/libcxx/include/exception b/libcxx/include/exception
index 5eff8e3f8a4bf..64463e02cb16a 100644
--- a/libcxx/include/exception
+++ b/libcxx/include/exception
@@ -47,7 +47,7 @@ terminate_handler set_terminate(terminate_handler  f ) noexcept;
 terminate_handler get_terminate() noexcept;
 [[noreturn]] void terminate() noexcept;
 
-bool uncaught_exception()  noexcept;
+bool uncaught_exception()  noexcept;  // deprecated in C++17, removed in C++20
 int  uncaught_exceptions() noexcept;  // C++17
 
 typedef unspecified exception_ptr;
diff --git a/libcxx/modules/std/exception.inc b/libcxx/modules/std/exception.inc
index 8e802c7065e0f..0c110e6e743fb 100644
--- a/libcxx/modules/std/exception.inc
+++ b/libcxx/modules/std/exception.inc
@@ -21,6 +21,5 @@ export namespace std {
   using std::terminate;
   using std::terminate_handler;
   using std::throw_with_nested;
-  using std::uncaught_exception;
   using std::uncaught_exceptions;
 } // namespace std
diff --git a/libcxx/src/exception.cpp b/libcxx/src/exception.cpp
index ddb186bf8048f..ac6324cd9fe35 100644
--- a/libcxx/src/exception.cpp
+++ b/libcxx/src/exception.cpp
@@ -6,6 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define _LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION
+#define _LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 #include <exception>
 #include <new>
 #include <typeinfo>
diff --git a/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp b/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp
index e368ce177b317..6fa4cb22070c8 100644
--- a/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp
+++ b/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp
@@ -7,6 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: no-exceptions
+
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // test uncaught_exception
 
 #include <exception>

mordante

Thanks! This looks mostly good, I like to have a quick review after addressing the review comments.

libcxx/docs/ReleaseNotes/20.rst

libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp

- Remove meaningless `TODO`. - Add `uncaught_exeption.depr_in_cxx17.verify.cpp`

github-actions · 2024-08-03T16:34:17Z

✅ With the latest revision this PR passed the C/C++ code formatter.

mordante

Thanks! LGTM modulo one minor issue I missed in the previous review.

libcxx/modules/std/exception.inc

ldionne

LGTM with nits.

libcxx/docs/ReleaseNotes/20.rst

libcxx/docs/Status/Cxx17.rst

Nits in release notes.

frederick-vs-ja requested a review from a team as a code owner August 3, 2024 15:09

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Aug 3, 2024

mordante self-assigned this Aug 3, 2024

mordante reviewed Aug 3, 2024

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frederick-vs-ja changed the title ~~[libc++] Remove and deprecate uncaught_exception~~ [libc++] Deprecate and remove uncaught_exception Aug 3, 2024

Address @mordante's review comments

efcd488

- Remove meaningless `TODO`. - Add `uncaught_exeption.depr_in_cxx17.verify.cpp`

frederick-vs-ja added 2 commits August 4, 2024 00:34

Clang-format

5d8ef45

Merge branch 'main' into remove-uncaught_exception

7d78ec1

mordante approved these changes Aug 4, 2024

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frederick-vs-ja added 2 commits August 4, 2024 21:13

Make uncaught_exception restorable in std modules

7922ea6

Merge branch 'main' into remove-uncaught_exception

dad71e8

ldionne approved these changes Aug 5, 2024

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frederick-vs-ja and others added 3 commits August 6, 2024 00:01

Address @ldionne's review comments

d5e2c1c

Nits in release notes.

Merge branch 'main' into remove-uncaught_exception

f39e8a3

Merge branch 'main' into remove-uncaught_exception

2900120

ldionne approved these changes Aug 27, 2024

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ldionne merged commit 4ea2c73 into llvm:main Aug 27, 2024
8 of 13 checks passed

frederick-vs-ja deleted the remove-uncaught_exception branch August 28, 2024 06:42

frederick-vs-ja mentioned this pull request Aug 28, 2024

P0619R4: Reviewing Deprecated Facilities of C++17 for C++20 #99985

Closed

frederick-vs-ja mentioned this pull request Sep 8, 2024

[libc++] std::uncaught_exceptions is provided in all standard modes while __cpp_lib_uncaught_exceptions is not #100515

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