Index: include/clang/Parse/Parser.h =================================================================== --- include/clang/Parse/Parser.h +++ include/clang/Parse/Parser.h @@ -506,6 +506,12 @@ Kind == tok::annot_module_end || Kind == tok::annot_module_include; } + /// \brief Checks if the \p Level is valid for use in a fold expression. + bool isFoldOperator(prec::Level Level) const; + + /// \brief Checks if the \p Kind is a valid operator for fold expressions. + bool isFoldOperator(tok::TokenKind Kind) const; + /// \brief Initialize all pragma handlers. void initializePragmaHandlers(); Index: lib/Parse/ParseExpr.cpp =================================================================== --- lib/Parse/ParseExpr.cpp +++ lib/Parse/ParseExpr.cpp @@ -266,11 +266,12 @@ return false; } -static bool isFoldOperator(prec::Level Level) { +bool Parser::isFoldOperator(prec::Level Level) const { return Level > prec::Unknown && Level != prec::Conditional; } -static bool isFoldOperator(tok::TokenKind Kind) { - return isFoldOperator(getBinOpPrecedence(Kind, false, true)); + +bool Parser::isFoldOperator(tok::TokenKind Kind) const { + return isFoldOperator(getBinOpPrecedence(Kind, GreaterThanIsOperator, true)); } /// \brief Parse a binary expression that starts with \p LHS and has a Index: test/Parser/cxx1z-fold-expressions.cpp =================================================================== --- test/Parser/cxx1z-fold-expressions.cpp +++ test/Parser/cxx1z-fold-expressions.cpp @@ -43,3 +43,20 @@ (int)(undeclared_junk + ...) + // expected-error {{undeclared}} (int)(a + ...); // expected-error {{does not contain any unexpanded}} } + +// fold-operator can be '>' or '>>'. +template constexpr bool greaterThan() { return (N > ...); } +template constexpr int rightShift() { return (N >> ...); } + +static_assert(greaterThan<2, 1>()); +static_assert(rightShift<10, 1>() == 5); + +template constexpr auto Identity = V; + +// Support fold operators within templates. +template constexpr int nestedFoldOperator() { + return Identity<(Identity<0> >> ... >> N)> + + Identity<(N >> ... >> Identity<0>)>; +} + +static_assert(nestedFoldOperator<3, 1>() == 1);