https://github.com/yronglin updated https://github.com/llvm/llvm-project/pull/192073
>From d5c3cd1f77a34e6b0b281d2a40f23a16dc760457 Mon Sep 17 00:00:00 2001 From: yronglin <[email protected]> Date: Tue, 14 Apr 2026 22:44:09 +0800 Subject: [PATCH 1/2] [NFC][Clang] Add test for P2843R3 - Preprocessing is never undefined Signed-off-by: yronglin <[email protected]> --- clang/docs/ReleaseNotes.rst | 4 ++++ clang/test/Preprocessor/p2843r3.cpp | 35 +++++++++++++++++++++++++++++ clang/www/cxx_status.html | 2 +- 3 files changed, 40 insertions(+), 1 deletion(-) create mode 100644 clang/test/Preprocessor/p2843r3.cpp diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 3e2d287d1eb1f..859b7e999848a 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -133,6 +133,10 @@ C++ Language Changes C++2c Feature Support ^^^^^^^^^^^^^^^^^^^^^ +- Implemented `P2843R3 <https://wg21.link/P2843R3>`_ Preprocessing is never undefined. + The constructs it makes ill-formed were already diagnosed by Clang under + ``-pedantic``; no behavior change, just conformance. + C++23 Feature Support ^^^^^^^^^^^^^^^^^^^^^ diff --git a/clang/test/Preprocessor/p2843r3.cpp b/clang/test/Preprocessor/p2843r3.cpp new file mode 100644 index 0000000000000..53c272390527c --- /dev/null +++ b/clang/test/Preprocessor/p2843r3.cpp @@ -0,0 +1,35 @@ +// RUN: %clang_cc1 -std=c++26 -pedantic -verify -Wno-invalid-pp-token %s +// RUN: %clang_cc1 -std=c++23 -pedantic -verify -Wno-invalid-pp-token %s + +// P2843R3: Preprocessing is never undefined. +// These constructs were previously "undefined behavior" in the preprocessor; +// as of C++26 they are ill-formed (diagnostic required). Clang already +// diagnoses them under -pedantic, so this test just pins that behavior down. + +// [cpp.cond] A macro that expands to 'defined' in a conditional expression. +#define DEFINED defined +#if DEFINED(bar) // expected-warning {{macro expansion producing 'defined' has undefined behavior}} +#endif + +// [cpp.replace.general] A preprocessing directive inside the arguments of a +// function-like macro invocation. +#define FUNCTION_MACRO(...) +FUNCTION_MACRO( + #if 0 // expected-warning {{embedding a directive within macro arguments has undefined behavior}} + #endif +) + +// [cpp.concat] Concatenation that does not form a valid preprocessing token. +#define CONCAT(A, B) A ## B +CONCAT(=, >) // expected-error {{pasting formed '=>', an invalid preprocessing token}} +// expected-error@-1 {{expected unqualified-id}} + +// [cpp.predefined] #undef of a reserved identifier / builtin macro. +#undef defined // expected-error {{'defined' cannot be used as a macro name}} +#undef __DATE__ // expected-warning {{undefining builtin macro}} + +// [cpp.line] #line with a non-positive or out-of-range argument. +#line 0 // expected-warning {{#line directive with zero argument is a GNU extension}} +#line -1 // expected-error {{#line directive requires a positive integer argument}} +#line 2147483647 // ok, largest value required to be accepted +#line 2147483648 // expected-warning {{C requires #line number to be less than 2147483648, allowed as extension}} diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html index 2c834b07f9a8f..4a669ff4da8a1 100755 --- a/clang/www/cxx_status.html +++ b/clang/www/cxx_status.html @@ -330,7 +330,7 @@ <h2 id="cxx26">C++2c implementation status</h2> <tr> <td>Preprocessing is never undefined</td> <td><a href="https://wg21.link/P2843";>P2843R3</a></td> - <td class="none" align="center">No</td> + <td class="full" align="center">Clang 23</td> </tr> <!-- Kona, Fall 2025--> <tr> >From 3cf297853d16cb4215fb1b98468b4537c0c98406 Mon Sep 17 00:00:00 2001 From: yronglin <[email protected]> Date: Tue, 14 Apr 2026 23:00:19 +0800 Subject: [PATCH 2/2] Update ReleaseNotes Signed-off-by: yronglin <[email protected]> --- clang/docs/ReleaseNotes.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 859b7e999848a..8d69c4716620b 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -133,7 +133,7 @@ C++ Language Changes C++2c Feature Support ^^^^^^^^^^^^^^^^^^^^^ -- Implemented `P2843R3 <https://wg21.link/P2843R3>`_ Preprocessing is never undefined. +- Mark `P2843R3 <https://wg21.link/P2843R3>`_ Preprocessing is never undefined as implemented. The constructs it makes ill-formed were already diagnosed by Clang under ``-pedantic``; no behavior change, just conformance. _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
