diff options
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/cp/pt.cc | 26 | ||||
| -rw-r--r-- | gcc/testsuite/g++.dg/cpp1z/class-deduction-alias1.C | 3 |
2 files changed, 23 insertions, 6 deletions
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 1f0231f..eeebc4c 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -29909,8 +29909,6 @@ do_class_deduction (tree ptype, tree tmpl, tree init, && CLASS_PLACEHOLDER_TEMPLATE (TREE_TYPE (init)) == tmpl) return cp_build_qualified_type (TREE_TYPE (init), cp_type_quals (ptype)); - /* Look through alias templates that just rename another template. */ - tmpl = get_underlying_template (tmpl); if (!ctad_template_p (tmpl)) { if (complain & tf_error) @@ -29920,15 +29918,33 @@ do_class_deduction (tree ptype, tree tmpl, tree init, else if (cxx_dialect < cxx20 && DECL_ALIAS_TEMPLATE_P (tmpl)) { if (complain & tf_error) - error ("alias template deduction only available " - "with %<-std=c++20%> or %<-std=gnu++20%>"); - return error_mark_node; + { + /* Be permissive with equivalent alias templates. */ + tree u = get_underlying_template (tmpl); + diagnostic_t dk = (u == tmpl) ? DK_ERROR : DK_PEDWARN; + bool complained + = emit_diagnostic (dk, input_location, 0, + "alias template deduction only available " + "with %<-std=c++20%> or %<-std=gnu++20%>"); + if (u == tmpl) + return error_mark_node; + else if (complained) + { + inform (input_location, "use %qD directly instead", u); + tmpl = u; + } + } + else + return error_mark_node; } /* Wait until the initializer is non-dependent. */ if (type_dependent_expression_p (init)) return ptype; + /* Don't bother with the alias rules for an equivalent template. */ + tmpl = get_underlying_template (tmpl); + tree type = TREE_TYPE (tmpl); bool try_list_ctor = false; diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction-alias1.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction-alias1.C index 1ec90b5..ffa5f2b 100644 --- a/gcc/testsuite/g++.dg/cpp1z/class-deduction-alias1.C +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction-alias1.C @@ -1,5 +1,6 @@ // PR c++/103852 // { dg-do compile { target c++17 } } +// { dg-options "" } template <class T> struct b{}; template <class T, class T1 = b<T>> @@ -10,7 +11,7 @@ struct s s c(100); template <class T, class T1 = b<T>> using ss = s<T, T1>; // equivalent under proposed resolution of DR 1286 -ss tt(1); // OK +ss tt(1); // { dg-warning "alias template deduction" "" { target c++17_only } } template <class T, class T1 = T> using ss2 = s<T, T1>; // different default arg makes it non-equivalent |