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.
Does this make sense? Bootstrapped/regtested on x86_64-pc-linux-gnu.
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
--
2.34.1
