[libc++] Fix header deprecations #163356

philnik777 · 2025-10-14T10:11:17Z

Currently, there are no diagnostics issued when including a deprecated header, since the diagnostic is issued inside a system header. This patch fixes that by using #warning instead, which also simplifies the implementation of the deprecation warnings.

libcxx/test/extensions/clang/clang_modules_include.gen.py

libcxx/test/libcxx/transitive_includes.gen.py

libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp

llvmbot · 2025-10-23T16:17:23Z

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

Currently, there are no diagnostics issued when including a deprecated header, since the diagnostic is issued inside a system header. This patch fixes that by using #warning instead, which also simplifies the implementation of the deprecation warnings.

Full diff: https://github.com/llvm/llvm-project/pull/163356.diff

13 Files Affected:

(modified) libcxx/include/__config (+6)
(modified) libcxx/include/ccomplex (+3-11)
(modified) libcxx/include/ciso646 (+3-6)
(modified) libcxx/include/cstdalign (+3-10)
(modified) libcxx/include/cstdbool (+3-10)
(modified) libcxx/include/ctgmath (+2-11)
(modified) libcxx/test/extensions/clang/clang_modules_include.gen.py (+2-2)
(modified) libcxx/test/libcxx/transitive_includes.gen.py (+1-1)
(modified) libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp (+1-7)
(modified) libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp (+2-1)
(modified) libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp (+1-7)
(modified) libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp (+1-7)
(modified) libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp (+1-7)

diff --git a/libcxx/include/__config b/libcxx/include/__config
index b4c081dcdff1b..dfc101954bddb 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -721,6 +721,12 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DEPRECATED_(m)
 #  endif
 
+#  if defined(__DEPRECATED) && __DEPRECATED && !defined(_LIBCPP_DISABLE_DEPRECATION_WARNINGS) && !__building_module(std)
+#    define _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS 1
+#  else
+#    define _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS 0
+#  endif
+
 #  if !defined(_LIBCPP_CXX03_LANG)
 #    define _LIBCPP_DEPRECATED_IN_CXX11 _LIBCPP_DEPRECATED
 #  else
diff --git a/libcxx/include/ccomplex b/libcxx/include/ccomplex
index ee7e088aac54d..bade696b95c70 100644
--- a/libcxx/include/ccomplex
+++ b/libcxx/include/ccomplex
@@ -26,18 +26,10 @@
 #    pragma GCC system_header
 #  endif
 
-#  if _LIBCPP_STD_VER >= 20
-
-using __standard_header_ccomplex
-    _LIBCPP_DEPRECATED_("removed in C++20. Include <complex> instead.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_ccomplex _LIBCPP_NODEBUG                                    = __standard_header_ccomplex;
-
-#  elif _LIBCPP_STD_VER >= 17
-
-using __standard_header_ccomplex _LIBCPP_DEPRECATED_("Include <complex> instead.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_ccomplex _LIBCPP_NODEBUG = __standard_header_ccomplex;
-
+#  if _LIBCPP_STD_VER >= 17 && _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS
+#    warning <ccomplex> is removed in C++20. Include <complex> instead.
 #  endif
+
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_CCOMPLEX
diff --git a/libcxx/include/ciso646 b/libcxx/include/ciso646
index 34164362dc10d..f4b1d6fa78ce7 100644
--- a/libcxx/include/ciso646
+++ b/libcxx/include/ciso646
@@ -24,13 +24,10 @@
 #    pragma GCC system_header
 #  endif
 
-#  if _LIBCPP_STD_VER >= 20
-
-using __standard_header_ciso646
-    _LIBCPP_DEPRECATED_("removed in C++20. Include <version> instead.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_ciso646 _LIBCPP_NODEBUG                                     = __standard_header_ciso646;
-
+#  if _LIBCPP_STD_VER >= 20 && _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS
+#    warning <ciso646> is removed in C++20. Include <version> instead.
 #  endif
+
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_CISO646
diff --git a/libcxx/include/cstdalign b/libcxx/include/cstdalign
index 7f8dd1e1fbaf8..60b2963c10fb4 100644
--- a/libcxx/include/cstdalign
+++ b/libcxx/include/cstdalign
@@ -43,17 +43,10 @@ Macros:
 #  undef __alignof_is_defined
 #  define __alignof_is_defined 1
 
-#  if _LIBCPP_STD_VER >= 20
-
-using __standard_header_cstdalign _LIBCPP_DEPRECATED_("removed in C++20.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_cstdalign _LIBCPP_NODEBUG = __standard_header_cstdalign;
-
-#  elif _LIBCPP_STD_VER >= 17
-
-using __standard_header_cstdalign _LIBCPP_DEPRECATED _LIBCPP_NODEBUG = void;
-using __use_standard_header_cstdalign _LIBCPP_NODEBUG                = __standard_header_cstdalign;
-
+#  if _LIBCPP_STD_VER >= 17 && _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS
+#    warning <cstdalign> is removed in C++20.
 #  endif
+
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_CSTDALIGN
diff --git a/libcxx/include/cstdbool b/libcxx/include/cstdbool
index a432d5f08b9ae..78b98699460dc 100644
--- a/libcxx/include/cstdbool
+++ b/libcxx/include/cstdbool
@@ -31,17 +31,10 @@ Macros:
 #  undef __bool_true_false_are_defined
 #  define __bool_true_false_are_defined 1
 
-#  if _LIBCPP_STD_VER >= 20
-
-using __standard_header_cstdbool _LIBCPP_DEPRECATED_("removed in C++20.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_cstdbool _LIBCPP_NODEBUG                                      = __standard_header_cstdbool;
-
-#  elif _LIBCPP_STD_VER >= 17
-
-using __standard_header_cstdbool _LIBCPP_DEPRECATED _LIBCPP_NODEBUG = void;
-using __use_standard_header_cstdbool _LIBCPP_NODEBUG                = __standard_header_cstdbool;
-
+#  if _LIBCPP_STD_VER >= 17 && _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS
+#    warning <cstdbool> is removed in C++20.
 #  endif
+
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 
 #endif // _LIBCPP_CSTDBOOL
diff --git a/libcxx/include/ctgmath b/libcxx/include/ctgmath
index db0786f1e2c46..9a0049a38880f 100644
--- a/libcxx/include/ctgmath
+++ b/libcxx/include/ctgmath
@@ -28,17 +28,8 @@
 #    pragma GCC system_header
 #  endif
 
-#  if _LIBCPP_STD_VER >= 20
-
-using __standard_header_ctgmath
-    _LIBCPP_DEPRECATED_("removed in C++20. Include <cmath> and <complex> instead.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_ctgmath _LIBCPP_NODEBUG = __standard_header_ctgmath;
-
-#  elif _LIBCPP_STD_VER >= 17
-
-using __standard_header_ctgmath _LIBCPP_DEPRECATED_("Include <cmath> and <complex> instead.") _LIBCPP_NODEBUG = void;
-using __use_standard_header_ctgmath _LIBCPP_NODEBUG = __standard_header_ctgmath;
-
+#  if _LIBCPP_STD_VER >= 17 && _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS
+#    warning <ctgmath> is removed in C++20. Include <cmath> and <complex> instead.
 #  endif
 
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
diff --git a/libcxx/test/extensions/clang/clang_modules_include.gen.py b/libcxx/test/extensions/clang/clang_modules_include.gen.py
index 28661049d6e85..f21c2cc9fd805 100644
--- a/libcxx/test/extensions/clang/clang_modules_include.gen.py
+++ b/libcxx/test/extensions/clang/clang_modules_include.gen.py
@@ -50,7 +50,7 @@
     print(
         f"""\
 //--- {header}.compile.pass.cpp
-// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} -fmodules -fcxx-modules -fmodules-cache-path=%t -fsyntax-only
+// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} -fmodules -fcxx-modules -fmodules-cache-path=%t -fsyntax-only -Wno-deprecated
 
 {lit_header_restrictions.get(header, '')}
 {lit_header_undeprecations.get(header, '')}
@@ -62,7 +62,7 @@
 print(
     f"""\
 //--- import_std.compile.pass.mm
-// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} -fmodules -fcxx-modules -fmodules-cache-path=%t -fsyntax-only
+// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} -fmodules -fcxx-modules -fmodules-cache-path=%t -fsyntax-only -Wno-deprecated
 
 // REQUIRES: clang-modules-build
 
diff --git a/libcxx/test/libcxx/transitive_includes.gen.py b/libcxx/test/libcxx/transitive_includes.gen.py
index 6ed35af7e275e..2b643e1f2ad48 100644
--- a/libcxx/test/libcxx/transitive_includes.gen.py
+++ b/libcxx/test/libcxx/transitive_includes.gen.py
@@ -89,7 +89,7 @@
 // UNSUPPORTED: LIBCXX-FREEBSD-FIXME
 
 // RUN: mkdir %t
-// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} --trace-includes -fshow-skipped-includes --preprocess > /dev/null 2> %t/trace-includes.txt
+// RUN: %{{cxx}} %s %{{flags}} %{{compile_flags}} -Wno-deprecated --trace-includes -fshow-skipped-includes --preprocess > /dev/null 2> %t/trace-includes.txt
 // RUN: %{{python}} %{{libcxx-dir}}/test/libcxx/transitive_includes/to_csv.py %t/trace-includes.txt > %t/actual_transitive_includes.csv
 // RUN: cat %{{libcxx-dir}}/test/libcxx/transitive_includes/%{{cxx_std}}.csv | awk '/^{escaped_header} / {{ print }}' > %t/expected_transitive_includes.csv
 // RUN: diff -w %t/expected_transitive_includes.csv %t/actual_transitive_includes.csv
diff --git a/libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp b/libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp
index 0eaf82ce5cef0..f63c971f9592f 100644
--- a/libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp
+++ b/libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp
@@ -14,12 +14,6 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
-#include "test_macros.h"
-
 #include <ccomplex>
 
-#if TEST_STD_VER >= 20
-// expected-warning@ccomplex:* {{'__standard_header_ccomplex' is deprecated: removed in C++20. Include <complex> instead.}}
-#else
-// expected-warning@ccomplex:* {{'__standard_header_ccomplex' is deprecated: Include <complex> instead.}}
-#endif
+// expected-warning@ccomplex:* {{<ccomplex> is removed in C++20. Include <complex> instead.}}
diff --git a/libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp b/libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp
index 04acd10081548..32b57033331c8 100644
--- a/libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp
+++ b/libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp
@@ -15,4 +15,5 @@
 // UNSUPPORTED: clang-modules-build
 
 #include <ciso646>
-// expected-warning@ciso646:* {{'__standard_header_ciso646' is deprecated: removed in C++20. Include <version> instead.}}
+
+// expected-warning@ciso646:* {{<ciso646> is removed in C++20. Include <version> instead.}}
diff --git a/libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp b/libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp
index dc9f1af55b3f1..258e82cfe0ad2 100644
--- a/libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp
+++ b/libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp
@@ -14,12 +14,6 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
-#include "test_macros.h"
-
 #include <cstdalign>
 
-#if TEST_STD_VER >= 20
-// expected-warning@cstdalign:* {{'__standard_header_cstdalign' is deprecated: removed in C++20.}}
-#else
-// expected-warning@cstdalign:* {{'__standard_header_cstdalign' is deprecated}}
-#endif
+// expected-warning@cstdalign:* {{<cstdalign> is removed in C++20.}}
diff --git a/libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp b/libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp
index eddefe14d35ea..5c89cfad27c3d 100644
--- a/libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp
+++ b/libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp
@@ -14,12 +14,6 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
-#include "test_macros.h"
-
 #include <cstdbool>
 
-#if TEST_STD_VER >= 20
-// expected-warning@cstdbool:* {{'__standard_header_cstdbool' is deprecated: removed in C++20.}}
-#else
-// expected-warning@cstdbool:* {{'__standard_header_cstdbool' is deprecated}}
-#endif
+// expected-warning@cstdbool:* {{<cstdbool> is removed in C++20.}}
diff --git a/libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp b/libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp
index 097ab1643d15a..1ada3768f894d 100644
--- a/libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp
+++ b/libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp
@@ -14,12 +14,6 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
-#include "test_macros.h"
-
 #include <ctgmath>
 
-#if TEST_STD_VER >= 20
-// expected-warning@ctgmath:* {{'__standard_header_ctgmath' is deprecated: removed in C++20. Include <cmath> and <complex> instead.}}
-#else
-// expected-warning@ctgmath:* {{'__standard_header_ctgmath' is deprecated: Include <cmath> and <complex> instead.}}
-#endif
+// expected-warning@ctgmath:* {{<ctgmath> is removed in C++20. Include <cmath> and <complex> instead.}}

libcxx/include/ccomplex

nico · 2025-11-21T16:13:43Z

This emits warnings for deprecated headers pulled in by system headers, e.g.:

In file included from ../../ios/chrome/browser/shared/ui/util/uikit_ui_util.mm:7:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Headers/Accelerate.h:20:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Headers/../Frameworks/vecLib.framework/Headers/vecLib.h:111:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Frameworks/vecLib.framework/Headers/vForce.h:50:
gen/third_party/libc++/src/include/ciso646:28:6: error: <ciso646> is removed in C++20. Include <version> instead. [-Werror,-W#warnings]
   28 | #    warning <ciso646> is removed in C++20. Include <version> instead.

That's not actionable for users.

What's a good path forward here?

philnik777 · 2025-11-21T16:31:36Z

This emits warnings for deprecated headers pulled in by system headers, e.g.:

In file included from ../../ios/chrome/browser/shared/ui/util/uikit_ui_util.mm:7:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Headers/Accelerate.h:20:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Headers/../Frameworks/vecLib.framework/Headers/vecLib.h:111:
In file included from sdk/xcode_links/iPhoneSimulator26.0.sdk/System/Library/Frameworks/Accelerate.framework/Frameworks/vecLib.framework/Headers/vForce.h:50:
gen/third_party/libc++/src/include/ciso646:28:6: error: <ciso646> is removed in C++20. Include <version> instead. [-Werror,-W#warnings]
   28 | #    warning <ciso646> is removed in C++20. Include <version> instead.

That's not actionable for users.

What's a good path forward here?

Urgh. I didn't expect that. I guess #168041 is more urgent than I thought.

nico · 2025-11-21T16:37:27Z

Oh, that's a very elegant approach!

Any chance we could revert this here until a bit until the clang change is in, so we don't have to block a libc++ update on a clang update? We kind of urgently want to roll in #168894 as it fixes a correctness issue.

I suppose we could add a file called ciso646 on our end and put it in the include search path first on iOS and put something akin to

#pragma clang diagnostic push
#pragma clang diagnostic ignored "deprecated-declarations"
#include_next <ciso646>
#pragma clang diagnostic pop

in it, but that feels a bit yucky…

philnik777 · 2025-11-21T16:45:36Z

In the interest of reducing churn and avoiding unrelated regressions I'd be more comfortable with defining _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS to 0 until we have Clang updated. Would that work for you?

nico · 2025-11-21T16:50:45Z

That would effectively get us back to the behavior before this PR (i.e. users never see deprecation warnings for headers from libc++ in practice), yes? If so, yes, that sounds like a good temporary workaround.

philnik777 · 2025-11-21T16:59:57Z

Yes, exactly. I guess we're also removing the diagnostic for people using -Wsystem-header or stuff like that, but I really don't care TBH. We're not supporting that stuff anyways.

nico · 2025-11-21T18:49:36Z

Sounds good. Are you making a PR?

philnik777 · 2025-11-24T09:14:42Z

I can make one.

nico · 2025-11-24T14:13:44Z

I can make one.

=> #169305

Thanks :)

Currently, there are no diagnostics issued when including a deprecated header, since the diagnostic is issued inside a system header. This patch fixes that by using `#warning` instead, which also simplifies the implementation of the deprecation warnings.

philnik777 force-pushed the simplify_header_deprecations branch 2 times, most recently from 3f18fc7 to 1d5093e Compare October 14, 2025 11:30

philnik777 changed the title ~~[libc++] Simplify how headers are deprecated~~ [libc++] Fix header deprecations Oct 15, 2025

philnik777 force-pushed the simplify_header_deprecations branch 2 times, most recently from 3861df3 to ddaebf4 Compare October 17, 2025 12:36

ldionne requested changes Oct 23, 2025

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ldionne marked this pull request as ready for review October 23, 2025 16:16

ldionne requested a review from a team as a code owner October 23, 2025 16:16

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Oct 23, 2025

philnik777 force-pushed the simplify_header_deprecations branch 2 times, most recently from a83b41f to b1d3271 Compare October 27, 2025 16:04

ldionne approved these changes Nov 10, 2025

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philnik777 force-pushed the simplify_header_deprecations branch from b1d3271 to c99b635 Compare November 14, 2025 11:16

[libc++] Simplify how headers are deprecated

30d301b

philnik777 force-pushed the simplify_header_deprecations branch from c99b635 to 30d301b Compare November 14, 2025 12:48

philnik777 merged commit 75792d6 into llvm:main Nov 18, 2025
80 checks passed

philnik777 deleted the simplify_header_deprecations branch November 18, 2025 15:05

[libc++] Fix header deprecations #163356

[libc++] Fix header deprecations #163356

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