https://github.com/osamakader updated https://github.com/llvm/llvm-project/pull/166004
>From 649ca4009961f3cc4ceae88fa8477f0d381f788f Mon Sep 17 00:00:00 2001 From: Osama Abdelkader <[email protected]> Date: Sat, 1 Nov 2025 19:53:55 +0200 Subject: [PATCH] [clang] Reject 'auto' storage class with type specifier in C++ Previously, clang allowed 'auto int x = 1;' in C++ as an extension (for C compatibility), emitting only a warning. This was confusing since 'auto' in C++11+ is a type specifier, not a storage class. This patch: - Adds a new error diagnostic 'err_auto_type_specifier' - Updates the parser to emit an error (instead of warning) when 'auto' is used as a storage class with a type specifier in C++ mode - Preserves C23 behavior where 'auto int' is valid - Adds comprehensive tests Fixes #164273 Signed-off-by: Osama Abdelkader <[email protected]> --- .../clang/Basic/DiagnosticParseKinds.td | 2 ++ clang/lib/Parse/ParseDecl.cpp | 21 ++++++++--- .../test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp | 36 ++++++++++++------- .../dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp | 2 +- .../dcl.spec/dcl.type/dcl.spec.auto/p3.cpp | 7 +++- clang/test/CXX/drs/cwg3xx.cpp | 8 +++-- clang/test/Parser/cxx-auto-type-specifier.cpp | 22 ++++++++++++ clang/test/SemaCXX/auto-cxx0x.cpp | 2 +- clang/test/SemaCXX/class.cpp | 7 ++-- clang/test/SemaCXX/static-data-member.cpp | 7 +++- 10 files changed, 86 insertions(+), 28 deletions(-) create mode 100644 clang/test/Parser/cxx-auto-type-specifier.cpp diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td index e5e071f43fa75..baf91b107b8c4 100644 --- a/clang/include/clang/Basic/DiagnosticParseKinds.td +++ b/clang/include/clang/Basic/DiagnosticParseKinds.td @@ -399,6 +399,8 @@ def err_requires_clause_on_declarator_not_declaring_a_function : Error< "trailing requires clause can only be used when declaring a function">; def err_requires_clause_inside_parens : Error< "trailing requires clause should be placed outside parentheses">; +def err_auto_type_specifier : Error< + "'auto' cannot be combined with a type specifier in C++">; def ext_auto_storage_class : ExtWarn< "'auto' storage class specifier is not permitted in C++11, and will not " "be supported in future releases">, InGroup<DiagGroup<"auto-storage-class">>; diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp index 7e4a164e34eda..1ca182167e1e5 100644 --- a/clang/lib/Parse/ParseDecl.cpp +++ b/clang/lib/Parse/ParseDecl.cpp @@ -4095,11 +4095,22 @@ void Parser::ParseDeclarationSpecifiers( case tok::kw_auto: if (getLangOpts().CPlusPlus11 || getLangOpts().C23) { if (isKnownToBeTypeSpecifier(GetLookAheadToken(1))) { - isInvalid = DS.SetStorageClassSpec(Actions, DeclSpec::SCS_auto, Loc, - PrevSpec, DiagID, Policy); - if (!isInvalid && !getLangOpts().C23) - Diag(Tok, diag::ext_auto_storage_class) - << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc()); + // In C++ (not C23), 'auto' cannot be combined with a type specifier. + // However, OpenCL has its own error handling for this case. + if (getLangOpts().CPlusPlus && !getLangOpts().C23 && + !getLangOpts().OpenCLCPlusPlus) { + // In C++11+, 'auto' cannot be combined with a type specifier. + // Don't set the storage class specifier to avoid Sema emitting a + // redundant error (GCC only emits one error for this case: "two or + // more data types in declaration"). + isInvalid = true; + PrevSpec = "auto"; + DiagID = diag::err_auto_type_specifier; + } else { + // C23 allows 'auto' as storage class with type specifier. + isInvalid = DS.SetStorageClassSpec(Actions, DeclSpec::SCS_auto, Loc, + PrevSpec, DiagID, Policy); + } } else isInvalid = DS.SetTypeSpecType(DeclSpec::TST_auto, Loc, PrevSpec, DiagID, Policy); diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp index 723a79628116c..da8732dc6e62c 100644 --- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp +++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp @@ -5,14 +5,18 @@ // The auto or register specifiers can be applied only to names of objects // declared in a block (6.3) or to function parameters (8.4). -auto int ao; // expected-error {{illegal storage class on file-scoped variable}} +auto int ao; #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{illegal storage class on file-scoped variable}} #endif -auto void af(); // expected-error {{illegal storage class on function}} +auto void af(); #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{illegal storage class on function}} #endif register int ro; // expected-error {{illegal storage class on file-scoped variable}} @@ -25,13 +29,17 @@ register int ro; // expected-error {{illegal storage class on file-scoped variab register void rf(); // expected-error {{illegal storage class on function}} struct S { - auto int ao; // expected-error {{storage class specified for a member declaration}} + auto int ao; #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{storage class specified for a member declaration}} #endif - auto void af(); // expected-error {{storage class specified for a member declaration}} + auto void af(); #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{storage class specified for a member declaration}} #endif register int ro; // expected-error {{storage class specified for a member declaration}} @@ -40,19 +48,21 @@ struct S { void foo(auto int ap, register int rp) { #if __cplusplus >= 201703L -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} // expected-error@-3 {{ISO C++17 does not allow 'register' storage class specifier}} #elif __cplusplus >= 201103L -// expected-warning@-5 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-5 {{'auto' cannot be combined with a type specifier in C++}} // expected-warning@-6 {{'register' storage class specifier is deprecated}} #endif auto int abo; #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} #endif - auto void abf(); // expected-error {{illegal storage class on function}} + auto void abf(); #if __cplusplus >= 201103L // C++11 or later -// expected-warning@-2 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{illegal storage class on function}} #endif register int rbo; diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp index e8f12156a4242..983119d6af8d0 100644 --- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp +++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp @@ -56,7 +56,7 @@ namespace p3_example { auto x = 5; const auto *v = &x, u = 6; static auto y = 0.0; - auto int r; // expected-warning {{storage class}} expected-error {{file-scope}} + auto int r; // expected-error {{'auto' cannot be combined with a type specifier in C++}} static_assert(is_same<decltype(x), int>(), ""); static_assert(is_same<decltype(v), const int*>(), ""); diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp index 440c78201293b..0a2688ee288ae 100644 --- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp +++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp @@ -42,7 +42,12 @@ void p3example() { static auto y = 0.0; // In C++98: 'auto' storage class specifier is redundant and incompatible with C++0x // In C++0x: 'auto' storage class specifier is not permitted in C++0x, and will not be supported in future releases - auto int r; // expected-warning {{'auto' storage class specifier}} + auto int r; +#if __cplusplus >= 201103L + // expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else + // expected-warning@-4 {{'auto' storage class specifier}} +#endif same<__typeof(x), int> xHasTypeInt; same<__typeof(v), const int*> vHasTypeConstIntPtr; diff --git a/clang/test/CXX/drs/cwg3xx.cpp b/clang/test/CXX/drs/cwg3xx.cpp index bbd87c060801a..73b9d513bf3e2 100644 --- a/clang/test/CXX/drs/cwg3xx.cpp +++ b/clang/test/CXX/drs/cwg3xx.cpp @@ -1732,11 +1732,13 @@ namespace cwg395 { // cwg395: 3.0 namespace cwg396 { // cwg396: 3.0 void f() { auto int a(); - // since-cxx11-error@-1 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} - // expected-error@-2 {{illegal storage class on function}} + // since-cxx11-error@-1 {{'auto' cannot be combined with a type specifier in C++}} + // cxx98-error@-2 {{illegal storage class on function}} + // since-cxx11-warning@-3 {{empty parentheses interpreted as a function declaration}} + // since-cxx11-note@-4 {{replace parentheses with an initializer to declare a variable}} int (i); // #cwg396-i auto int (i); - // since-cxx11-error@-1 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} + // since-cxx11-error@-1 {{'auto' cannot be combined with a type specifier in C++}} // expected-error@-2 {{redefinition of 'i'}} // expected-note@#cwg396-i {{previous definition is here}} } diff --git a/clang/test/Parser/cxx-auto-type-specifier.cpp b/clang/test/Parser/cxx-auto-type-specifier.cpp new file mode 100644 index 0000000000000..f34195934cc85 --- /dev/null +++ b/clang/test/Parser/cxx-auto-type-specifier.cpp @@ -0,0 +1,22 @@ +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++17 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++23 %s + +// Test that 'auto' cannot be combined with a type specifier in C++. +void f() { + auto int x = 1; // expected-error {{'auto' cannot be combined with a type specifier in C++}} + auto char c = 'a'; // expected-error {{'auto' cannot be combined with a type specifier in C++}} + auto float f = 1.0f; // expected-error {{'auto' cannot be combined with a type specifier in C++}} + auto double d = 1.0; // expected-error {{'auto' cannot be combined with a type specifier in C++}} + auto long l = 1L; // expected-error {{'auto' cannot be combined with a type specifier in C++}} +} + +// Test that regular 'auto' (type deduction) still works in C++. +void h() { + auto x = 1; + auto y = 2.0; + auto z = 'c'; +} + diff --git a/clang/test/SemaCXX/auto-cxx0x.cpp b/clang/test/SemaCXX/auto-cxx0x.cpp index 07687b6066790..2662319b900cd 100644 --- a/clang/test/SemaCXX/auto-cxx0x.cpp +++ b/clang/test/SemaCXX/auto-cxx0x.cpp @@ -1,7 +1,7 @@ // RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11 // RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++1y void f() { - auto int a; // expected-warning {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} + auto int a; // expected-error {{'auto' cannot be combined with a type specifier in C++}} int auto b; // expected-error{{cannot combine with previous 'int' declaration specifier}} } diff --git a/clang/test/SemaCXX/class.cpp b/clang/test/SemaCXX/class.cpp index f1e02d5158aac..e0aa09dca82e4 100644 --- a/clang/test/SemaCXX/class.cpp +++ b/clang/test/SemaCXX/class.cpp @@ -2,11 +2,12 @@ // RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx98 -Wc++11-compat %s -std=c++98 class C { public: - auto int errx; // expected-error {{storage class specified for a member declaration}} + auto int errx; #if __cplusplus <= 199711L - // expected-warning@-2 {{'auto' storage class specifier is redundant}} + // expected-error@-2 {{storage class specified for a member declaration}} + // expected-warning@-3 {{'auto' storage class specifier is redundant and incompatible with C++11}} #else - // expected-warning@-4 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}} + // expected-error@-5 {{'auto' cannot be combined with a type specifier in C++}} #endif register int erry; // expected-error {{storage class specified for a member declaration}} extern int errz; // expected-error {{storage class specified for a member declaration}} diff --git a/clang/test/SemaCXX/static-data-member.cpp b/clang/test/SemaCXX/static-data-member.cpp index fb63da9b40099..49c016dee892b 100644 --- a/clang/test/SemaCXX/static-data-member.cpp +++ b/clang/test/SemaCXX/static-data-member.cpp @@ -13,7 +13,12 @@ double ABC::a = 1.0; extern double ABC::b = 1.0; // expected-error {{static data member definition cannot specify a storage class}} static double ABC::c = 1.0; // expected-error {{'static' can only be specified inside the class definition}} __private_extern__ double ABC::d = 1.0; // expected-error {{static data member definition cannot specify a storage class}} -auto double ABC::e = 1.0; // expected-error {{static data member definition cannot specify a storage class}} +auto double ABC::e = 1.0; +#if __cplusplus >= 201103L +// expected-error@-2 {{'auto' cannot be combined with a type specifier in C++}} +#else +// expected-error@-4 {{static data member definition cannot specify a storage class}} +#endif #if __cplusplus < 201703L register double ABC::f = 1.0; // expected-error {{static data member definition cannot specify a storage class}} #endif _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
