https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101988
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:0c0f453c4af4880c522c8472c33eef42bee9eda1 commit r12-6894-g0c0f453c4af4880c522c8472c33eef42bee9eda1 Author: Marek Polacek <pola...@redhat.com> Date: Wed Jan 26 17:29:19 2022 -0500 c++: new-expr of array of deduced class tmpl [PR101988] In r12-1933 I attempted to implement DR2397 aka allowing int a[3]; auto (&r)[3] = a; by removing the type_uses_auto check in create_array_type_for_decl. That may have gone too far, because it also allows arrays of CLASS_PLACEHOLDER_TEMPLATE and it looks like [dcl.type.class.deduct] prohibits that: "...the declared type of the variable shall be cv T, where T is the placeholder." However, in /2 it explicitly states that "A placeholder for a deduced class type can also be used in the type-specifier-seq in the new-type-id or type-id of a new-expression." In this PR, it manifested by making us accept invalid template<class T> struct A { A(T); }; auto p = new A[]{1}; [expr.new]/2 says that such a construct is treated as an invented declaration of the form A x[]{1}; but, I think, that ought to be ill-formed as per above. So this patch sort of restores the create_array_type_for_decl check. I should mention that the difference between [] and [1] is due to cp_parser_new_type_id: if (*nelts == NULL_TREE) /* Leave [] in the declarator. */; and groktypename returning different types based on that. PR c++/101988 gcc/cp/ChangeLog: * decl.cc (create_array_type_for_decl): Reject forming an array of placeholder for a deduced class type. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction-new1.C: New test. * g++.dg/cpp23/auto-array2.C: New test.
