We were saying 'auto parameter not permitted' in a place where 'auto' is in
fact permitted in C++20, but a class template placeholder is not.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
* decl.c (grokdeclarator): Improve diagnostic for
disallowed CTAD placeholder.
gcc/testsuite/ChangeLog:
* g++.dg/other/pr88187.C: Adjust expected error.
* g++.dg/cpp2a/class-deduction-abbrev1.C: New test.
---
gcc/cp/decl.c | 10 ++++++++++
.../g++.dg/cpp2a/class-deduction-abbrev1.C | 13 +++++++++++++
gcc/testsuite/g++.dg/other/pr88187.C | 2 +-
3 files changed, 24 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-abbrev1.C
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 1e2bae4afba..0cf84a0750c 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -13145,6 +13145,16 @@ grokdeclarator (const cp_declarator *declarator,
if (decl_context == PARM && AUTO_IS_DECLTYPE (auto_node))
error_at (typespec_loc,
"cannot declare a parameter with %<decltype(auto)%>");
+ else if (tree c = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
+ {
+ auto_diagnostic_group g;
+ error_at (typespec_loc,
+ "class template placeholder %qE not permitted "
+ "in this context", c);
+ if (decl_context == PARM && cxx_dialect >= cxx20)
+ inform (typespec_loc, "use %<auto%> for an "
+ "abbreviated function template");
+ }
else
error_at (typespec_loc,
"%<auto%> parameter not permitted in this context");
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-abbrev1.C
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-abbrev1.C
new file mode 100644
index 00000000000..f9310090b5b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-abbrev1.C
@@ -0,0 +1,13 @@
+ // { dg-do compile { target c++20 } }
+
+template <class T> struct A { };
+template <class T> concept is_A = requires { A(T()); };
+
+void f(auto); // OK
+void f(is_A auto); // OK
+void f(A); // { dg-error "placeholder" }
+
+int main()
+{
+ f(A<int>());
+}
diff --git a/gcc/testsuite/g++.dg/other/pr88187.C
b/gcc/testsuite/g++.dg/other/pr88187.C
index ebdafddc634..13466d3ce57 100644
--- a/gcc/testsuite/g++.dg/other/pr88187.C
+++ b/gcc/testsuite/g++.dg/other/pr88187.C
@@ -4,4 +4,4 @@
template <int> struct A;
void f (A ()); // { dg-error "6:variable or field 'f' declared void" "" {
target c++14_down } }
// { dg-error "missing template arguments before '\\(' token"
"" { target c++14_down } .-1 }
- // { dg-error "'auto' parameter not permitted in this context"
"" { target c++17 } .-2 }
+ // { dg-error "placeholder .A. not permitted in this context"
"" { target c++17 } .-2 }
base-commit: d9288bd28e24c755a7216311ee5247e7c88270a6
--
2.27.0
