From 05708d6eef87a3dd0c68b1aed7f8d9c3824062b8 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Thu, 8 Apr 2021 13:07:37 -0400 Subject: c++: constrained CTAD for nested class template [PR97679] In the testcase below, we're crashing during constraint checking of the implicitly generated deduction guides for the nested class template A::B because we never substitute the outer template arguments (for A) into the constraint, neither ahead of time nor as part of satisfaction. Ideally we'd like to avoid substituting into a constraint ahead of time, but the "flattening" vector 'tsubst_args' is constructed under the assumption that all outer template arguments are already substituted in, and eliminating this assumption to yield a flattening vector that includes outer (generic) template arguments suitable for substituting into the constraint would be tricky and error-prone. So this patch takes the approximate approach of substituting the outer arguments into the constraint ahead of time, so that the subsequent substitution of 'tsubst_args' is coherent and so later satisfaction just works. gcc/cp/ChangeLog: PR c++/97679 * pt.c (build_deduction_guide): Document OUTER_ARGS. Substitute them into the propagated constraints. gcc/testsuite/ChangeLog: PR c++/97679 * g++.dg/cpp2a/concepts-ctad3.C: New test. --- gcc/cp/pt.c | 20 +++++++++++++++++--- gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C | 16 ++++++++++++++++ 2 files changed, 33 insertions(+), 3 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C (limited to 'gcc') diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 46b237f..842a58c 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -28602,7 +28602,8 @@ rewrite_tparm_list (tree oldelt, unsigned index, unsigned level, /* Returns a C++17 class deduction guide template based on the constructor CTOR. As a special case, CTOR can be a RECORD_TYPE for an implicit default guide, REFERENCE_TYPE for an implicit copy/move guide, or TREE_LIST for an - aggregate initialization guide. */ + aggregate initialization guide. OUTER_ARGS are the template arguments + for the enclosing scope of the class. */ static tree build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t complain) @@ -28728,7 +28729,15 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com if (fparms == error_mark_node) ok = false; if (ci) - ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor); + { + if (outer_args) + /* FIXME: We'd like to avoid substituting outer template + arguments into the constraint ahead of time, but the + construction of tsubst_args assumes that outer arguments + are already substituted in. */ + ci = tsubst_constraint_info (ci, outer_args, complain, ctor); + ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor); + } /* Parms are to have DECL_CHAIN tsubsted, which would be skipped if cp_unevaluated_operand. */ @@ -28744,7 +28753,12 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com fparms = tsubst_arg_types (fparms, targs, NULL_TREE, complain, ctor); fargs = tsubst (fargs, targs, complain, ctor); if (ci) - ci = tsubst_constraint_info (ci, targs, complain, ctor); + { + if (outer_args) + /* FIXME: As above. */ + ci = tsubst_constraint_info (ci, outer_args, complain, ctor); + ci = tsubst_constraint_info (ci, targs, complain, ctor); + } } --processing_template_decl; diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C new file mode 100644 index 0000000..3546b74 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C @@ -0,0 +1,16 @@ +// PR c++/97679 +// { dg-do compile { target c++20 } } + +template struct A { + template struct B { + B(T) requires V; + template B(T, U) requires V || (__is_same(T, char) && __is_same(U, int)); + }; +}; + +A::B x1(0); +A::B x2(0); // { dg-error "deduction|no match" } + +A::B y1(0, '0'); +A::B y2(0, '0'); // { dg-error "deduction|no match" } +A::B y3('0', 0); -- cgit v1.1