diff options
| author | Jason Merrill <jason@redhat.com> | 2022-04-04 11:56:38 -0400 |
|---|---|---|
| committer | Jason Merrill <jason@redhat.com> | 2022-04-05 12:29:33 -0400 |
| commit | 5d583d24200ac33a1cb281b7ddee9aad351151b5 (patch) | |
| tree | 1cfc2dfb4e7a0fffc6c757a414a607705c266a0a /gcc | |
| parent | 1de6612d994ada8edaab18bbc6afd8e9a57413aa (diff) | |
| download | gcc-5d583d24200ac33a1cb281b7ddee9aad351151b5.zip gcc-5d583d24200ac33a1cb281b7ddee9aad351151b5.tar.gz gcc-5d583d24200ac33a1cb281b7ddee9aad351151b5.tar.bz2 | |
c++: alias template equivalence and CTAD [PR103852]
I had been thinking about DR1286 "equivalence" as meaning generally
interchangeable, but looking back at the proposed resolution in the context
of this PR, I see that it's just about use as a template argument. So let's
give a pedwarn if we look through a renaming alias.
PR c++/103852
DR 1286
gcc/cp/ChangeLog:
* pt.cc (do_class_deduction): Pedwarn for renaming alias in C++17.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1z/class-deduction-alias1.C: Expect warning.
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 |