Author: Aaron Ballman Date: 2025-05-13T10:59:55-04:00 New Revision: e3f87e15910a5f1c5552fc3ef57e7dda3f68901a
URL: https://github.com/llvm/llvm-project/commit/e3f87e15910a5f1c5552fc3ef57e7dda3f68901a DIFF: https://github.com/llvm/llvm-project/commit/e3f87e15910a5f1c5552fc3ef57e7dda3f68901a.diff LOG: [C] Fix a false-positive with tentative defn compat (#139738) C++ has a carve-out that makes a declaration with 'extern' explicitly specified and no initializer be a declaration rather than a definition. We now account for that to silence a diagnostic with: ``` extern const int i; const int i = 12; ``` which is valid C++. Addresses an issue that was brought up via post-commit review. Added: Modified: clang/lib/Sema/SemaDecl.cpp clang/test/Sema/warn-tentative-defn-compat.c Removed: ################################################################################ diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index 5a45198a7ce02..152f3f340cd50 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -4755,8 +4755,16 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) { return; } } else { - Diag(New->getLocation(), diag::warn_cxx_compat_tentative_definition) << New; - Diag(Old->getLocation(), diag::note_previous_declaration); + // C++ may not have a tentative definition rule, but it has a diff erent + // rule about what constitutes a definition in the first place. See + // [basic.def]p2 for details, but the basic idea is: if the old declaration + // contains the extern specifier and doesn't have an initializer, it's fine + // in C++. + if (Old->getStorageClass() != SC_Extern || Old->hasInit()) { + Diag(New->getLocation(), diag::warn_cxx_compat_tentative_definition) + << New; + Diag(Old->getLocation(), diag::note_previous_declaration); + } } if (haveIncompatibleLanguageLinkages(Old, New)) { diff --git a/clang/test/Sema/warn-tentative-defn-compat.c b/clang/test/Sema/warn-tentative-defn-compat.c index 02f3db99992f1..6e6b70df2cf7b 100644 --- a/clang/test/Sema/warn-tentative-defn-compat.c +++ b/clang/test/Sema/warn-tentative-defn-compat.c @@ -20,4 +20,7 @@ int k = 12; // expected-warning {{duplicate declaration of 'k' is invalid in C++ cxx-error {{redefinition of 'k'}} // Cannot have two declarations with initializers, that is a redefinition in -// both C and C++. +// both C and C++. However, C++ does have a diff erent definition of what makes +// a declaration a definition. +extern const int a; +const int a = 12; // Okay in C and C++ _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
