Talking about the declarator form doesn't help when fixing that would get you a different error about placeholders not being valid in a parameter.
This also adds a <> fixit, which isn't enough for most templates, but is a start. Tested x86_64-pc-linux-gnu, applying to trunk. PR c++/106793 gcc/cp/ChangeLog: * decl.cc (grokdeclarator): Improve placeholder diagnostics. * parser.cc (cp_parser_type_id_1): Add fixit. gcc/testsuite/ChangeLog: * g++.dg/cpp23/auto-array2.C: Adjust. * g++.dg/cpp1z/class-deduction113.C: New test. --- gcc/cp/decl.cc | 30 ++++++++++++------- gcc/cp/parser.cc | 7 +++-- .../g++.dg/cpp1z/class-deduction113.C | 5 ++++ gcc/testsuite/g++.dg/cpp23/auto-array2.C | 4 +-- 4 files changed, 32 insertions(+), 14 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction113.C diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index 6d20765f40c..4665a29a24d 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -12407,14 +12407,20 @@ grokdeclarator (const cp_declarator *declarator, if (cxx_dialect >= cxx17 && type && is_auto (type) && innermost_code != cdk_function + /* Placeholder in parm gets a better error below. */ + && !(decl_context == PARM || decl_context == CATCHPARM) && id_declarator && declarator != id_declarator) if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (type)) - { - error_at (typespec_loc, "template placeholder type %qT must be followed " - "by a simple declarator-id", type); - inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here", tmpl); - type = error_mark_node; - } + { + auto_diagnostic_group g; + gcc_rich_location richloc (typespec_loc); + richloc.add_fixit_insert_after ("<>"); + error_at (&richloc, "missing template argument list after %qE; " + "for deduction, template placeholder must be followed " + "by a simple declarator-id", tmpl); + inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here", tmpl); + type = error_mark_node; + } staticp = 0; inlinep = decl_spec_seq_has_spec_p (declspecs, ds_inline); @@ -12892,6 +12898,7 @@ grokdeclarator (const cp_declarator *declarator, { if (!funcdecl_p || !dguide_name_p (unqualified_id)) { + auto_diagnostic_group g; error_at (typespec_loc, "deduced class " "type %qD in function return type", DECL_NAME (tmpl)); @@ -13837,12 +13844,15 @@ grokdeclarator (const cp_declarator *declarator, 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); + gcc_rich_location richloc (typespec_loc); + richloc.add_fixit_insert_after ("<>"); + error_at (&richloc, + "missing template argument list after %qE; template " + "placeholder not permitted in parameter", c); if (decl_context == PARM && cxx_dialect >= cxx20) - inform (typespec_loc, "use %<auto%> for an " + inform (typespec_loc, "or use %<auto%> for an " "abbreviated function template"); + inform (DECL_SOURCE_LOCATION (c), "%qD declared here", c); } else error_at (typespec_loc, diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc index 289c2142e45..841ba6ed997 100644 --- a/gcc/cp/parser.cc +++ b/gcc/cp/parser.cc @@ -24397,8 +24397,11 @@ cp_parser_type_id_1 (cp_parser *parser, cp_parser_flags flags, location_t loc = type_specifier_seq.locations[ds_type_spec]; if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node)) { - error_at (loc, "missing template arguments after %qT", - auto_node); + auto_diagnostic_group g; + gcc_rich_location richloc (loc); + richloc.add_fixit_insert_after ("<>"); + error_at (&richloc, "missing template arguments after %qE", + tmpl); inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here", tmpl); } diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction113.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction113.C new file mode 100644 index 00000000000..8f6908e2746 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction113.C @@ -0,0 +1,5 @@ +// PR c++/106793 + +template <class T> struct A { A(T); }; +template <class T> void f(A *a); // { dg-error "placeholder.*parameter" "" { target c++17 } } +// { dg-error "" "" { target c++14_down } .-1 } diff --git a/gcc/testsuite/g++.dg/cpp23/auto-array2.C b/gcc/testsuite/g++.dg/cpp23/auto-array2.C index 06431685b30..3fc2eae3cea 100644 --- a/gcc/testsuite/g++.dg/cpp23/auto-array2.C +++ b/gcc/testsuite/g++.dg/cpp23/auto-array2.C @@ -5,7 +5,7 @@ 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" } +A (*p3)[3] = &a; // { dg-error "template placeholder" } auto (&r)[3] = a; A<int> (&r2)[3] = a; -A (&r3)[3] = a; // { dg-error "template placeholder type" } +A (&r3)[3] = a; // { dg-error "template placeholder" } base-commit: a961ad1b13b9c294d4565344912b8e35ba71b369 -- 2.31.1