Index: clang/include/clang/Parse/Parser.h =================================================================== --- clang/include/clang/Parse/Parser.h +++ clang/include/clang/Parse/Parser.h @@ -2639,7 +2639,8 @@ // which standard permits but we don't supported yet, for example, attributes // appertain to decl specifiers. void ProhibitCXX11Attributes(ParsedAttributesWithRange &Attrs, - unsigned DiagID); + unsigned DiagID, + bool DiagnoseEmptyAttrs = false); /// Skip C++11 and C2x attributes and return the end location of the /// last one. Index: clang/lib/Parse/ParseDecl.cpp =================================================================== --- clang/lib/Parse/ParseDecl.cpp +++ clang/lib/Parse/ParseDecl.cpp @@ -1607,7 +1607,30 @@ } void Parser::ProhibitCXX11Attributes(ParsedAttributesWithRange &Attrs, - unsigned DiagID) { + unsigned DiagID, bool DiagnoseEmptyAttrs) { + + if (DiagnoseEmptyAttrs && Attrs.empty() && Attrs.Range.isValid()) { + // An attribute list has been parsed, but it was empty. + // This is the case for [[]]. + auto &SM = PP.getSourceManager(); + auto &LangOpts = getLangOpts(); + Token FirstLSquare; + Lexer::getRawToken(Attrs.Range.getBegin(), FirstLSquare, SM, LangOpts); + + if (FirstLSquare.is(tok::l_square)) { + llvm::Optional SecondLSquare = + Lexer::findNextToken(FirstLSquare.getLocation(), SM, LangOpts); + + if (SecondLSquare && SecondLSquare->is(tok::l_square)) { + // The attribute range starts with [[, but is empty. So this must + // be [[]], which we are supposed to diagnose because + // DiagnoseEmptyAttrs is true. + Diag(Attrs.Range.getBegin(), DiagID) << Attrs.Range; + return; + } + } + } + for (const ParsedAttr &AL : Attrs) { if (!AL.isCXX11Attribute() && !AL.isC2xAttribute()) continue; Index: clang/lib/Parse/ParseDeclCXX.cpp =================================================================== --- clang/lib/Parse/ParseDeclCXX.cpp +++ clang/lib/Parse/ParseDeclCXX.cpp @@ -1836,7 +1836,8 @@ } else if (TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation && TUK == Sema::TUK_Declaration) { // This is an explicit instantiation of a class template. - ProhibitAttributes(attrs); + ProhibitCXX11Attributes(attrs, diag::err_attributes_not_allowed, + /*DiagnoseEmptyAttrs=*/true); TagOrTempResult = Actions.ActOnExplicitInstantiation( getCurScope(), TemplateInfo.ExternLoc, TemplateInfo.TemplateLoc, Index: clang/test/Parser/cxx0x-attributes.cpp =================================================================== --- clang/test/Parser/cxx0x-attributes.cpp +++ clang/test/Parser/cxx0x-attributes.cpp @@ -179,6 +179,7 @@ struct [[]] Template t; // expected-error {{an attribute list cannot appear here}} struct [[]] ::template Template u; // expected-error {{an attribute list cannot appear here}} template struct [[]] Template; // expected-error {{an attribute list cannot appear here}} +template struct __attribute__((pure)) Template; // We still allow GNU-style attributes here template <> struct [[]] Template; enum [[]] E1 {};