diff options
author | Marek Polacek <polacek@redhat.com> | 2022-04-14 13:48:15 -0400 |
---|---|---|
committer | Marek Polacek <polacek@redhat.com> | 2022-04-15 09:59:11 -0400 |
commit | ccae4443c8322d9d82a19a1e7c689413a122a478 (patch) | |
tree | 6386a8ba124f3532d233d5038bd9667dc8e8f4f4 | |
parent | a54137c88061c7495728fc6b8dfd0474e812b2cb (diff) |
c++: wrong error with variadic concept [PR105268]
Here we issue a wrong error for the
template<typename T = S<C_many<int>>> void g();
line in the testcase. I surmise that's because we mistakenly parse
C_many<int> as a placeholder-type-specifier, and things go wrong from
there. We are in a default argument so we should reject parsing C_many<int>
as a placeholder-type-specifier, which would mean creating a new parameter.
We want C_many<int> to be a concept-id instead.
It's interesting to see why the same problem didn't occur for C_one<int>.
In that case, cp_parser_placeholder_type_specifier -> finish_type_constraints
-> build_type_constraint -> build_concept_check -> build_standard_check ->
coerce_template_parms fails the parse here:
8916 nargs = inner_args ? NUM_TMPL_ARGS (inner_args) : 0;
8917 if ((nargs - variadic_args_p > nparms && !variadic_p)
8918 || (nargs < nparms - variadic_p
8919 && require_all_args
8920 && !variadic_args_p
8921 && (!use_default_args
8922 || (TREE_VEC_ELT (parms, nargs) != error_mark_node
8923 && !TREE_PURPOSE (TREE_VEC_ELT (parms, nargs))))))
8924 {
8925 bad_nargs:
...
8943 return error_mark_node;
because nargs is 2 (the targs are <WILDCARD_DECL, int>) while nparms is
1 (for the one 'typename' in the tparam list of C_one). But for
C_many<int> variadic_p is true so we don't return error_mark_node but
<type_argument_pack>.
This patch does not issue any error for the !tentative case because
I didn't figure out how to trigger that. So it adds an assert instead.
PR c++/105268
gcc/cp/ChangeLog:
* parser.cc (cp_parser_placeholder_type_specifier): Return
error_mark_node when trying to build up a constrained parameter in
a default argument.
gcc/testsuite/ChangeLog:
* g++.dg/concepts/variadic6.C: New test.
-rw-r--r-- | gcc/cp/parser.cc | 11 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/concepts/variadic6.C | 20 |
2 files changed, 30 insertions, 1 deletions
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc index bfd16e1ef62..169e6a62f5f 100644 --- a/gcc/cp/parser.cc +++ b/gcc/cp/parser.cc @@ -20041,7 +20041,16 @@ cp_parser_placeholder_type_specifier (cp_parser *parser, location_t loc, /* In a template parameter list, a type-parameter can be introduced by type-constraints alone. */ if (processing_template_parmlist && !placeholder) - return build_constrained_parameter (con, proto, args); + { + /* In a default argument we may not be creating new parameters. */ + if (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN) + { + /* If this assert turns out to be false, do error() instead. */ + gcc_assert (tentative); + return error_mark_node; + } + return build_constrained_parameter (con, proto, args); + } /* Diagnose issues placeholder issues. */ if (!flag_concepts_ts diff --git a/gcc/testsuite/g++.dg/concepts/variadic6.C b/gcc/testsuite/g++.dg/concepts/variadic6.C new file mode 100644 index 00000000000..0b386b0cd6d --- /dev/null +++ b/gcc/testsuite/g++.dg/concepts/variadic6.C @@ -0,0 +1,20 @@ +// PR c++/105268 +// { dg-do compile { target concepts } } + +template<typename> concept C_one = true; +template<typename...> concept C_many = true; + +template<bool B> struct S { }; + +template<typename T = S<C_one<int>>> void f(); +template<typename T = S<C_many<int>>> void g(); + +void +fn (auto a = S<C_one<int>>{}) +{ +} + +void +fn2 (auto a = S<C_many<int>>{}) +{ +} |