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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id f127-20020a379c85000000b0069c921d6576sm649393qke.76.2022.04.14.19.32.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Apr 2022 19:32:47 -0700 (PDT) Message-ID: Date: Thu, 14 Apr 2022 22:32:45 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] c++: wrong error with variadic concept [PR105268] To: Marek Polacek , GCC Patches , Patrick Palka References: <20220414202419.420912-1-polacek@redhat.com> From: Jason Merrill In-Reply-To: <20220414202419.420912-1-polacek@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-14.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Apr 2022 02:32:56 -0000 On 4/14/22 16:24, Marek Polacek wrote: > Here we issue a wrong error for the > > template>> void g(); > > line in the testcase. I surmise that's because we mistakenly parse > C_many as a placeholder-type-specifier, and things go wrong from > there. We are in a default argument so we should reject parsing C_many > as a placeholder-type-specifier, which would mean creating a new parameter. > We want C_many to be a concept-id instead. > > It's interesting to see why the same problem didn't occur for C_one. > 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 ) while nparms is > 1 (for the one 'typename' in the tparam list of C_one). But for > C_many variadic_p is true so we don't return error_mark_node but > . > > This patch does not issue any error for the !tentative case because > I didn't figure out how to trigger that. Then I'd add an assert that tentative is true. OK with that change. > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > 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. > --- > gcc/cp/parser.cc | 7 ++++++- > gcc/testsuite/g++.dg/concepts/variadic6.C | 20 ++++++++++++++++++++ > 2 files changed, 26 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/g++.dg/concepts/variadic6.C > > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc > index bfd16e1ef62..dfb613168b6 100644 > --- a/gcc/cp/parser.cc > +++ b/gcc/cp/parser.cc > @@ -20041,7 +20041,12 @@ 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) > + 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 concept C_one = true; > +template concept C_many = true; > + > +template struct S { }; > + > +template>> void f(); > +template>> void g(); > + > +void > +fn (auto a = S>{}) > +{ > +} > + > +void > +fn2 (auto a = S>{}) > +{ > +} > > base-commit: 82536fbb8a7d150b829650378e0ba07dad5c8fb8