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[clang] Reject 'auto' storage class with type specifier in C++ #166004

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[clang] Reject 'auto' storage class with type specifier in C++ #166004

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2 changes: 2 additions & 0 deletions clang/include/clang/Basic/DiagnosticParseKinds.td
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Original file line number Diff line number Diff line change
Expand Up @@ -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">;
def ext_auto_storage_class : ExtWarn<
"'auto' storage class specifier is not permitted in C++11, and will not "
Comment on lines 404 to 405
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This pr makes ext_auto_storage_class unused, so we should remove it

"be supported in future releases">, InGroup<DiagGroup<"auto-storage-class">>;
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22 changes: 17 additions & 5 deletions clang/lib/Parse/ParseDecl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4095,11 +4095,23 @@ 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.
// OpenCL is excluded here because Sema emits a more specific error
// message for OpenCL (e.g., "does not support the 'auto' storage
// class specifier").
if (!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";
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Suggested change
PrevSpec = "auto";
PrevSpec = Tok.getIdentifierInfo()->getNameStart();

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);
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36 changes: 23 additions & 13 deletions clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp
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Expand Up @@ -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}}
#else
// expected-error@-4 {{illegal storage class on file-scoped variable}}
Comment on lines +10 to +12
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It'd be slightly easier to review this file if we used -verify= and different prefixes instead of preprocessor conditionals, but I don't insist on a change for this PR either unless others have strong feelings.

#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}}
#else
// expected-error@-4 {{illegal storage class on function}}
#endif

register int ro; // expected-error {{illegal storage class on file-scoped variable}}
Expand All @@ -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}}
#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}}
#else
// expected-error@-4 {{storage class specified for a member declaration}}
#endif

register int ro; // expected-error {{storage class specified for a member declaration}}
Expand All @@ -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}}
// 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}}
// 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}}
#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}}
#else
// expected-error@-4 {{illegal storage class on function}}
#endif

register int rbo;
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2 changes: 1 addition & 1 deletion clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp
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Expand Up @@ -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}}

static_assert(is_same<decltype(x), int>(), "");
static_assert(is_same<decltype(v), const int*>(), "");
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7 changes: 6 additions & 1 deletion clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp
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Expand Up @@ -42,7 +42,12 @@ void p3example() {
static auto y = 0.0;
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This line should also be diagnosed in C++98 mode... this seems to be a preexisting bug: https://godbolt.org/z/3cza618cx (we have a similar bug with register: https://godbolt.org/z/zs5918YY4)

GitHub is too useless to let me put this comment on the correct line, but line 40 has a similar C++98 bug: https://godbolt.org/z/xEozMhe6z because there's no type specifier there, and line 41 does as well for the same reason.

Hmmm, it seems we're treating type deduction as an extension in C++98 mode, but we don't list it in the language extensions page as such and we don't issue pedantic diagnostics for it. @zygoloid do you recall if this was an intentional extension or not? Regardless, because this is existing behavior, nothing needs to change as part of this PR.

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Hmmm, it seems we're treating type deduction as an extension in C++98 mode, but we don't list it in the language extensions page as such and we don't issue pedantic diagnostics for it. @zygoloid do you recall if this was an intentional extension or not?

I see a diagnostic for it appearing in all of your test cases:

<source>:2:10: warning: 'auto' type specifier is a C++11 extension [-Wc++11-extensions]
    2 |   static auto y = 0.0;
      |

... and -pedantic-errors does promote that to an error. So yeah, this is an intentional extension, from the general category of feature from a later language mode accepted in earlier language modes, but I guess the table in our documentation is incomplete -- it only seems to include the C++ features with feature test macros (plus one that I guess postdates the table).

If we want that table to be complete, it's probably worth going through the diagnostics in the -Wc++XY-extensions groups and making sure they're all listed. All the relevant extensions should have diagnostics already.

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I see a diagnostic for it appearing in all of your test cases:

Ugh, yeah, I am seeing that now, I think I was looking at the wrong output before. :-D

Yeah, I think the table just needs to be updated, that doesn't need to be a part of this PR though. Thanks!

// 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}}
#else
// expected-warning@-4 {{'auto' storage class specifier}}
#endif

same<__typeof(x), int> xHasTypeInt;
same<__typeof(v), const int*> vHasTypeConstIntPtr;
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8 changes: 5 additions & 3 deletions clang/test/CXX/drs/cwg3xx.cpp
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Expand Up @@ -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}}
// cxx98-error@-1 {{illegal storage class on function}}
// since-cxx11-error@-2 {{'auto' cannot be combined with a type specifier}}
// 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}}
// expected-error@-2 {{redefinition of 'i'}}
// expected-note@#cwg396-i {{previous definition is here}}
}
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22 changes: 22 additions & 0 deletions clang/test/Parser/cxx-auto-type-specifier.cpp
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@@ -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}}
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One more test to add:

template <typename Ty>
void g() {
  auto Ty x;
}

void test() {
  g<float>();
}

auto char c = 'a'; // expected-error {{'auto' cannot be combined with a type specifier}}
auto float f = 1.0f; // expected-error {{'auto' cannot be combined with a type specifier}}
auto double d = 1.0; // expected-error {{'auto' cannot be combined with a type specifier}}
auto long l = 1L; // expected-error {{'auto' cannot be combined with a type specifier}}
}

// Test that regular 'auto' (type deduction) still works in C++.
void h() {
auto x = 1;
auto y = 2.0;
auto z = 'c';
}

2 changes: 1 addition & 1 deletion clang/test/SemaCXX/auto-cxx0x.cpp
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@@ -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}}
int auto b; // expected-error{{cannot combine with previous 'int' declaration specifier}}
}

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7 changes: 4 additions & 3 deletions clang/test/SemaCXX/class.cpp
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Expand Up @@ -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}}
#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}}
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7 changes: 6 additions & 1 deletion clang/test/SemaCXX/static-data-member.cpp
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Expand Up @@ -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}}
#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