[Clang] Warn with -Wpre-c23-compat instead of -Wpre-c++17-compat for u8 character literals in C23

[MitalAshok]

No description provided.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Mital Ashok (MitalAshok)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/97210.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/include/clang/Basic/DiagnosticLexKinds.td (+3)
• (modified) clang/lib/Lex/Lexer.cpp (+3-1)
• (modified) clang/test/Sema/pre-c2x-compat.c (+1)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c720e47dbe35b..d2939ef7a875c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -627,6 +627,8 @@ Improvements to Clang's diagnostics
   used rather than when they are needed for constant evaluation or when code is generated for them.
   The check is now stricter to prevent crashes for some unsupported declarations (Fixes #GH95495).
 
+- Clang now warns for u8 character literals used in C23 with ``-Wpre-c23-compat`` instead of ``-Wpre-c++17-compat``.
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index 12d7b8c0205ee..fc14bb6aa2165 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -283,6 +283,9 @@ def warn_cxx98_compat_unicode_literal : Warning<
 def warn_cxx14_compat_u8_character_literal : Warning<
   "unicode literals are incompatible with C++ standards before C++17">,
   InGroup<CXXPre17Compat>, DefaultIgnore;
+def warn_c17_compat_u8_character_literal : Warning<
+  "unicode literals are incompatible with C standards before C23">,
+  InGroup<CPre23Compat>, DefaultIgnore;
 def warn_cxx11_compat_user_defined_literal : Warning<
   "identifier after literal will be treated as a user-defined literal suffix "
   "in C++11">, InGroup<CXX11Compat>, DefaultIgnore;
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index e59c7805b3862..c61d81e93d990 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -2428,7 +2428,9 @@ bool Lexer::LexCharConstant(Token &Result, const char *CurPtr,
                           ? diag::warn_cxx98_compat_unicode_literal
                           : diag::warn_c99_compat_unicode_literal);
     else if (Kind == tok::utf8_char_constant)
-      Diag(BufferPtr, diag::warn_cxx14_compat_u8_character_literal);
+      Diag(BufferPtr, LangOpts.CPlusPlus
+                          ? diag::warn_cxx14_compat_u8_character_literal
+                          : diag::warn_c17_compat_u8_character_literal);
   }
 
   char C = getAndAdvanceChar(CurPtr, Result);
diff --git a/clang/test/Sema/pre-c2x-compat.c b/clang/test/Sema/pre-c2x-compat.c
index fad472f1f72d5..15bb9b58349fa 100644
--- a/clang/test/Sema/pre-c2x-compat.c
+++ b/clang/test/Sema/pre-c2x-compat.c
@@ -1,3 +1,4 @@
 // RUN: %clang_cc1 %s -std=c2x -Wpre-c2x-compat -pedantic -fsyntax-only -verify
 
 int digit_seps = 123'456; // expected-warning {{digit separators are incompatible with C standards before C23}}
+unsigned char u8_char = u8'x'; // expected-warning {{unicode literals are incompatible with C standards before C23}}

[cor3ntin]

It's a bit weird to have an extension warning given we seem to not support u8 in older language modes at all
https://www.godbolt.org/z/1KrqGeT1q

I think we should support the extension before in addition of having a warning for it
@AaronBallman

[AaronBallman]

It's a bit weird to have an extension warning given we seem to not support u8 in older language modes at all https://www.godbolt.org/z/1KrqGeT1q

I think we should support the extension before in addition of having a warning for it @AaronBallman

It's not an extension warning (it's marked Warning not Extension or ExtWarn), and the warning is telling you exactly that -- u8 in older language modes may not work pre-C23.

[AaronBallman]

LGTM!