Clang accepts invalid parenthesized template name in deduction guide declaration

[zygoloid]

Along the same lines as #152018, but a somewhat different case:

template<typename T> struct X {};
(X)() -> X<int>;

Clang accepts, but this is invalid: the syntax for deduction guides does not allow parentheses around the template-name.

While GCC accepts this, other implementations (EDG, MSVC) do not, so it would probably make sense for clang to also reject.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Richard Smith (zygoloid)

Along the same lines as #152018, but a somewhat different case:

template<typename T> struct X {};
(X)() -> X<int>;

Clang accepts, but this is invalid: the syntax for deduction guides does not allow parentheses around the template-name.

While GCC accepts this, other implementations (EDG, MSVC) do not, so it would probably make sense for clang to also reject.