On 1/26/22 18:55, Marek Polacek wrote:
In r12-1933 I attempted to implement DR2397 aka allowingint 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. Does this make sense? Bootstrapped/regtested on x86_64-pc-linux-gnu.
OK.
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. --- gcc/cp/decl.cc | 12 ++++++++++++ .../g++.dg/cpp1z/class-deduction-new1.C | 16 ++++++++++++++++ gcc/testsuite/g++.dg/cpp23/auto-array2.C | 11 +++++++++++ 3 files changed, 39 insertions(+) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction-new1.C create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-array2.C diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index 6534a7fd320..10e6956117e 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -11087,6 +11087,18 @@ create_array_type_for_decl (tree name, tree type, tree size, location_t loc) if (type == error_mark_node || size == error_mark_node) return error_mark_node;+ /* [dcl.type.class.deduct] prohibits forming an array of placeholder+ for a deduced class type. */ + if (is_auto (type) && CLASS_PLACEHOLDER_TEMPLATE (type)) + { + if (name) + error_at (loc, "%qD declared as array of template placeholder " + "type %qT", name, type); + else + error ("creating array of template placeholder type %qT", type); + return error_mark_node; + } + /* If there are some types which cannot be array elements, issue an error-message and return. */ switch (TREE_CODE (type)) diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction-new1.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction-new1.C new file mode 100644 index 00000000000..70283353619 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction-new1.C @@ -0,0 +1,16 @@ +// PR c++/101988 +// { dg-do compile { target c++17 } } + +template<typename T> +struct A { + A(T); + A(); +}; +auto p1 = new A[]{1}; // { dg-error "creating array of template placeholder type" } +auto p2 = new A[1]{1}; // { dg-error "invalid use of placeholder" } +auto p3 = new A<int>[]{1}; +auto p4 = new A<int>[1]{1}; +auto p5 = new A[]{1, 2}; // { dg-error "creating array of template placeholder type" } +auto p6 = new A<int>[]{1, 2}; +auto p7 = new A<int>[]{A(1), A(1)}; +auto p8 = new A<int>[2]{A(1), A(1)}; diff --git a/gcc/testsuite/g++.dg/cpp23/auto-array2.C b/gcc/testsuite/g++.dg/cpp23/auto-array2.C new file mode 100644 index 00000000000..06431685b30 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-array2.C @@ -0,0 +1,11 @@ +// PR c++/101988 +// { dg-do compile { target c++17 } } + +template<class T> struct A { A(); }; +A<int> a[3]; +auto (*p)[3] = &a; +A<int> (*p2)[3] = &a; +A (*p3)[3] = &a; // { dg-error "template placeholder type" } +auto (&r)[3] = a; +A<int> (&r2)[3] = a; +A (&r3)[3] = a; // { dg-error "template placeholder type" } base-commit: fd5b0488ad5e4f29b65238e06a2d65b7de120235
