[clang] ce7c196 - [Clang] Ignore -fchar8_t in C (#138716)

[via cfe-commits]

Author: cor3ntin
Date: 2025-05-08T12:15:05+02:00
New Revision: ce7c1963b914931817dd983f488cc0b810187b3a

URL: https://github.com/llvm/llvm-project/commit/ce7c1963b914931817dd983f488cc0b810187b3a
DIFF: https://github.com/llvm/llvm-project/commit/ce7c1963b914931817dd983f488cc0b810187b3a.diff

LOG: [Clang] Ignore -fchar8_t in C (#138716)

In C, `char8_t` is an alias to unsigned char, and should never be a
keyword.

Fixes #55373

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/Driver/Options.td
    clang/test/Lexer/char8_t.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c52e285bde627..7f68fd877e4e2 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -319,6 +319,8 @@ Modified Compiler Flags
 
 - The ``-mexecute-only`` and ``-mpure-code`` flags are now accepted for AArch64 targets. (#GH125688)
 
+- The ``-fchar8_t`` flag is no longer considered in non-C++ languages modes. (#GH55373)
+
 Removed Compiler Flags
 -------------------------
 

diff  --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 351e1ad4e1b03..c8bd81bdf1e43 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3911,7 +3911,8 @@ defm char8__t : BoolFOption<"char8_t",
   LangOpts<"Char8">, Default<cpp20.KeyPath>,
   PosFlag<SetTrue, [], [ClangOption], "Enable">,
   NegFlag<SetFalse, [], [ClangOption], "Disable">,
-  BothFlags<[], [ClangOption, CC1Option], " C++ builtin type char8_t">>;
+  BothFlags<[], [ClangOption, CC1Option], " C++ builtin type char8_t">>,
+  ShouldParseIf<cplusplus.KeyPath>;
 def fshort_wchar : Flag<["-"], "fshort-wchar">, Group<f_Group>,
   HelpText<"Force wchar_t to be a short unsigned int">;
 def fno_short_wchar : Flag<["-"], "fno-short-wchar">, Group<f_Group>,

diff  --git a/clang/test/Lexer/char8_t.cpp b/clang/test/Lexer/char8_t.cpp
index d65597c68d8bc..2148609155186 100644
--- a/clang/test/Lexer/char8_t.cpp
+++ b/clang/test/Lexer/char8_t.cpp
@@ -5,6 +5,7 @@
 // RUN: %clang_cc1 -std=c++17 -verify %s
 // RUN: %clang_cc1 -std=c++17 -verify %s -fno-char8_t
 // RUN: %clang_cc1 -std=c++20 -verify %s -fno-char8_t
+// RUN: %clang_cc1 -x c -verify %s -fchar8_t
 
 #if defined(__cpp_char8_t) != defined(CHAR8_T)
 #error wrong setting for __cpp_char_t