Author: rnk Date: Thu Aug 15 12:45:28 2019 New Revision: 369043 URL: http://llvm.org/viewvc/llvm-project?rev=369043&view=rev Log: [Sema] Implement DR2386 for C++17 structured binding
Allow implementations to provide complete definitions of std::tuple_size<T>, but to omit the 'value' member to signal that T is not tuple-like. The Microsoft standard library implements std::tuple_size<const T> this way. If the value member exists, clang still validates that it is an ICE, but if it does not, then the type is considered to not be tuple-like. Fixes PR33236 Reviewers: rsmith Differential Revision: https://reviews.llvm.org/D66040 Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp cfe/trunk/test/CXX/dcl.decl/dcl.decomp/p3.cpp cfe/trunk/test/CXX/drs/dr23xx.cpp Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=369043&r1=369042&r2=369043&view=diff ============================================================================== --- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original) +++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Thu Aug 15 12:45:28 2019 @@ -1030,8 +1030,10 @@ static IsTupleLike isTupleLike(Sema &S, TemplateArgumentListInfo Args(Loc, Loc); Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T)); - // If there's no tuple_size specialization, it's not tuple-like. - if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/0)) + // If there's no tuple_size specialization or the lookup of 'value' is empty, + // it's not tuple-like. + if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) || + R.empty()) return IsTupleLike::NotTupleLike; // If we get this far, we've committed to the tuple interpretation, but @@ -1048,11 +1050,6 @@ static IsTupleLike isTupleLike(Sema &S, } } Diagnoser(R, Args); - if (R.empty()) { - Diagnoser.diagnoseNotICE(S, Loc, SourceRange()); - return IsTupleLike::Error; - } - ExprResult E = S.BuildDeclarationNameExpr(CXXScopeSpec(), R, /*NeedsADL*/false); if (E.isInvalid()) Modified: cfe/trunk/test/CXX/dcl.decl/dcl.decomp/p3.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/dcl.decl/dcl.decomp/p3.cpp?rev=369043&r1=369042&r2=369043&view=diff ============================================================================== --- cfe/trunk/test/CXX/dcl.decl/dcl.decomp/p3.cpp (original) +++ cfe/trunk/test/CXX/dcl.decl/dcl.decomp/p3.cpp Thu Aug 15 12:45:28 2019 @@ -12,7 +12,7 @@ void no_tuple_size_2() { auto [x, y] = A struct Bad1 { int a, b; }; template<> struct std::tuple_size<Bad1> {}; -void no_tuple_size_3() { auto [x, y] = Bad1(); } // expected-error {{cannot decompose this type; 'std::tuple_size<Bad1>::value' is not a valid integral constant expression}} +void no_tuple_size_3() { auto [x, y] = Bad1(); } // ok, omitting value is valid after DR2386 struct Bad2 {}; template<> struct std::tuple_size<Bad2> { const int value = 5; }; Modified: cfe/trunk/test/CXX/drs/dr23xx.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/drs/dr23xx.cpp?rev=369043&r1=369042&r2=369043&view=diff ============================================================================== --- cfe/trunk/test/CXX/drs/dr23xx.cpp (original) +++ cfe/trunk/test/CXX/drs/dr23xx.cpp Thu Aug 15 12:45:28 2019 @@ -40,6 +40,27 @@ namespace dr2353 { // dr2353: 9 #pragma clang __debug dump not_use_2 } +#if __cplusplus >= 201707L +// Otherwise, if the qualified-id std::tuple_size<E> names a complete class +// type **with a member value**, the expression std::tuple_size<E>::value shall +// be a well-formed integral constant expression +namespace dr2386 { // dr2386: 9 +struct Bad1 { int a, b; }; +struct Bad2 { int a, b; }; +} // namespace dr2386 +namespace std { +template <typename T> struct tuple_size; +template <> struct std::tuple_size<dr2386::Bad1> {}; +template <> struct std::tuple_size<dr2386::Bad2> { + static const int value = 42; +}; +} // namespace std +namespace dr2386 { +void no_value() { auto [x, y] = Bad1(); } +void wrong_value() { auto [x, y] = Bad2(); } // expected-error {{decomposes into 42 elements}} +} // namespace dr2386 +#endif + namespace dr2387 { // dr2387: 9 #if __cplusplus >= 201402L template<int> int a = 0; _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
