[Clang] disallow constexpr with auto and explicit type in C23

[a-tarasyuk]

Fixes #163090

---

This PR addresses the issue of Clang not diagnosing the invalid combination of constexpr,
auto, and an explicit type

constexpr auto int x = 0

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

Changes

Fixes #163090

---

This PR addresses the issue of Clang not diagnosing the invalid combination of constexpr,
auto, and an explicit type

constexpr auto int x = 0

---

Full diff: https://github.com/llvm/llvm-project/pull/163469.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Sema/DeclSpec.cpp (+1-1)
• (modified) clang/test/Parser/c2x-auto.c (+2)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index edb872c1f388d..de745e54a0cbd 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -269,6 +269,8 @@ Non-comprehensive list of changes in this release allocation functions with a token ID can be enabled via the ``-fsanitize=alloc-token`` flag. +- Clang now rejects the invalid use of ``constexpr`` with ``auto`` and an explicit type. (#GH163090) + New Compiler Flags ------------------ - New option ``-fno-sanitize-debug-trap-reasons`` added to disable emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``). diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp index 184d31ecd1e40..482cb1fe703fe 100644 --- a/clang/lib/Sema/DeclSpec.cpp +++ b/clang/lib/Sema/DeclSpec.cpp @@ -1369,7 +1369,7 @@ void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) { if (S.getLangOpts().C23 && getConstexprSpecifier() == ConstexprSpecKind::Constexpr && - StorageClassSpec == SCS_extern) { + (StorageClassSpec == SCS_extern || StorageClassSpec == SCS_auto)) { S.Diag(ConstexprLoc, diag::err_invalid_decl_spec_combination) << DeclSpec::getSpecifierName(getStorageClassSpec()) << SourceRange(getStorageClassSpecLoc()); diff --git a/clang/test/Parser/c2x-auto.c b/clang/test/Parser/c2x-auto.c index b878a5b7c42d4..b33b267841132 100644 --- a/clang/test/Parser/c2x-auto.c +++ b/clang/test/Parser/c2x-auto.c @@ -62,6 +62,8 @@ auto basic_usage(auto auto) { // c23-error {{'auto' not allowed in function pr int auto_cxx_decl = auto(0); // expected-error {{expected expression}} + constexpr auto int x = 0; // c23-error {{cannot combine with previous 'auto' declaration specifier}} \ + c17-error {{use of undeclared identifier 'constexpr'}} return c; } 

[Fznamznon]

Thank you for working on this!

[AaronBallman]

LGTM!

[Halalaluyafail3]

Why is the order of keywords here significant?