[Clang] Define __cpp_pack_indexing

[Sirraide]

Following the discussion on #101448, this defines __cpp_pack_indexing. Since pack indexing is currently supported in all language modes, the feature test macro is also defined in all language modes.

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (Sirraide)

Changes

Following the discussion on #101448, this defines __cpp_pack_indexing. Since pack indexing is currently supported in all language modes, the feature test macro is also defined in all language modes.

---

Full diff: https://github.com/llvm/llvm-project/pull/101956.diff

3 Files Affected:

• (modified) clang/docs/LanguageExtensions.rst (+1)
• (modified) clang/lib/Frontend/InitPreprocessor.cpp (+1)
• (modified) clang/test/Lexer/cxx-features.cpp (+4)

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 9dcb4ac9b75ca..be07f81cc41b0 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -1503,6 +1503,7 @@ Conditional ``explicit``                     __cpp_conditional_explicit       C+
 ``static operator()``                        __cpp_static_call_operator       C++23         C++03
 Attributes on Lambda-Expressions                                              C++23         C++11
 Attributes on Structured Bindings            __cpp_structured_bindings        C++26         C++03
+Pack Indexing                                __cpp_pack_indexing              C++26         C++03
 ``= delete ("should have a reason");``       __cpp_deleted_function           C++26         C++03
 -------------------------------------------- -------------------------------- ------------- -------------
 Designated initializers (N494)                                                C99           C89
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 17b9ca7cb9910..8e62461d8a181 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -763,6 +763,7 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
   Builder.defineMacro("__cpp_placeholder_variables", "202306L");
 
   // C++26 features supported in earlier language modes.
+  Builder.defineMacro("__cpp_pack_indexing", "202311L");
   Builder.defineMacro("__cpp_deleted_function", "202403L");
 
   if (LangOpts.Char8)
diff --git a/clang/test/Lexer/cxx-features.cpp b/clang/test/Lexer/cxx-features.cpp
index 4c2aa3ae2c544..08b732132228b 100644
--- a/clang/test/Lexer/cxx-features.cpp
+++ b/clang/test/Lexer/cxx-features.cpp
@@ -38,6 +38,10 @@
 #error "wrong value for __cpp_deleted_function"
 #endif
 
+#if check(pack_indexing, 202311, 202311, 202311, 202311, 202311, 202311, 202311)
+#error "wrong value for __cpp_pack_indexing"
+#endif
+
 #if check(placeholder_variables, 202306, 202306, 202306, 202306, 202306, 202306, 202306)
 #error "wrong value for __cpp_placeholder_variables"
 #endif

[cor3ntin]

LGTM.
I think we should backport to Clang 19. WDYT?

[Sirraide]

I think we should backport to Clang 19. WDYT?

That makes a lot of sense to me imo: the feature is already in Clang 19, this just makes it so we claim to support it too.

[Sirraide]

/cherry-pick c65afad

[llvmbot]

/pull-request #101965