As described in detail in comment #4 of this PR, when tentatively parsing a construct that can either be a type or an expression, if during the type parse we encounter an unexpected template placeholder, we need to simulate an error rather than issue a real error because the subsequent expression parse can still succeed.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk? gcc/cp/ChangeLog: PR c++/87709 * parser.c (cp_parser_type_id_1): If we see a template placeholder, first try simulating an error before issuing a real error. gcc/testsuite/ChangeLog: PR c++/87709 * g++.dg/cpp1z/class-deduction86.C: New test. --- gcc/cp/parser.c | 11 +++++++---- gcc/testsuite/g++.dg/cpp1z/class-deduction86.C | 16 ++++++++++++++++ 2 files changed, 23 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction86.C diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index fba516efa23..e1b1617da68 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -23270,10 +23270,13 @@ 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); - inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here", - tmpl); + if (!cp_parser_simulate_error (parser)) + { + error_at (loc, "missing template arguments after %qT", + auto_node); + inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here", + tmpl); + } } else if (parser->in_template_argument_list_p) error_at (loc, "%qT not permitted in template argument", diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction86.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction86.C new file mode 100644 index 00000000000..a198ed24ec6 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction86.C @@ -0,0 +1,16 @@ +// PR c++/87709 +// { dg-do compile { target c++17 } } + +template <class T> +struct lit { + lit(T) { } +}; + +template <class T> +int operator+(lit<T>, lit<T>) { + return 0; +} + +auto r2 = (lit(0)) + lit(0); + +static_assert(sizeof(lit(0))); -- 2.31.1.362.g311531c9de