Here we're crashing ultimately because the mechanism for delaying substitution into a requires-expression (or constexpr if) doesn't expect to see dependent args. But we end up capturing dependent args here when substituting into the default template argument during coerce_template_parms for the dependent specialization p<T>.
This patch enables the commented out code in add_extra_args for handling this situation. It turns out we also need to make a copy of the captured arguments so that coerce_template_parms doesn't later add to the argument, which would form an unexpected cycle. And we need to make tsubst_template_args more forgiving about missing template arguments, since the arguments we capture from coerce_template_parms are incomplete. Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk/11? PR c++/101181 gcc/cp/ChangeLog: * constraint.cc (tsubst_requires_expr): Pass complain/in_decl to add_extra_args. * cp-tree.h (add_extra_args): Add complain/in_decl parameters. * pt.c (build_extra_args): Make a copy of args. (add_extra_args): Add complain/in_decl parameters. Handle the case where the extra arguments are dependent. (tsubst_pack_expansion): Pass complain/in_decl to add_extra_args. (tsubst_template_args): Handle missing template arguments. (tsubst_expr) <case IF_STMT>: Pass complain/in_decl to add_extra_args. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-requires26.C: New test. * g++.dg/cpp2a/lambda-uneval16.C: New test. --- gcc/cp/constraint.cc | 3 +- gcc/cp/cp-tree.h | 2 +- gcc/cp/pt.c | 31 +++++++++---------- .../g++.dg/cpp2a/concepts-requires26.C | 18 +++++++++++ gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C | 22 +++++++++++++ 5 files changed, 58 insertions(+), 18 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc index 99d3ccc6998..4ee5215df50 100644 --- a/gcc/cp/constraint.cc +++ b/gcc/cp/constraint.cc @@ -2266,7 +2266,8 @@ tsubst_requires_expr (tree t, tree args, sat_info info) /* A requires-expression is an unevaluated context. */ cp_unevaluated u; - args = add_extra_args (REQUIRES_EXPR_EXTRA_ARGS (t), args); + args = add_extra_args (REQUIRES_EXPR_EXTRA_ARGS (t), args, + info.complain, info.in_decl); if (processing_template_decl) { /* We're partially instantiating a generic lambda. Substituting into diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 58da7460001..0a5f13489cc 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -7289,7 +7289,7 @@ extern void add_mergeable_specialization (bool is_decl, bool is_alias, tree outer, unsigned); extern tree add_to_template_args (tree, tree); extern tree add_outermost_template_args (tree, tree); -extern tree add_extra_args (tree, tree); +extern tree add_extra_args (tree, tree, tsubst_flags_t, tree); extern tree build_extra_args (tree, tree, tsubst_flags_t); /* in rtti.c */ diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 06116d16887..e4bdac087ad 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -12928,7 +12928,9 @@ extract_local_specs (tree pattern, tsubst_flags_t complain) tree build_extra_args (tree pattern, tree args, tsubst_flags_t complain) { - tree extra = args; + /* Make a copy of the extra arguments so that they won't get changed + from under us. */ + tree extra = copy_template_args (args); if (local_specializations) if (tree locals = extract_local_specs (pattern, complain)) extra = tree_cons (NULL_TREE, extra, locals); @@ -12939,7 +12941,7 @@ build_extra_args (tree pattern, tree args, tsubst_flags_t complain) normal template args to ARGS. */ tree -add_extra_args (tree extra, tree args) +add_extra_args (tree extra, tree args, tsubst_flags_t complain, tree in_decl) { if (extra && TREE_CODE (extra) == TREE_LIST) { @@ -12959,20 +12961,14 @@ add_extra_args (tree extra, tree args) gcc_assert (!TREE_PURPOSE (extra)); extra = TREE_VALUE (extra); } -#if 1 - /* I think we should always be able to substitute dependent args into the - pattern. If that turns out to be incorrect in some cases, enable the - alternate code (and add complain/in_decl parms to this function). */ - gcc_checking_assert (!uses_template_parms (extra)); -#else - if (!uses_template_parms (extra)) + if (uses_template_parms (extra)) { - gcc_unreachable (); + /* This can happen during dependent substitution into a requires-expr + or a lambda that uses constexpr if. */ extra = tsubst_template_args (extra, args, complain, in_decl); args = add_outermost_template_args (args, extra); } else -#endif args = add_to_template_args (extra, args); return args; } @@ -12998,7 +12994,7 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain, pattern = PACK_EXPANSION_PATTERN (t); /* Add in any args remembered from an earlier partial instantiation. */ - args = add_extra_args (PACK_EXPANSION_EXTRA_ARGS (t), args); + args = add_extra_args (PACK_EXPANSION_EXTRA_ARGS (t), args, complain, in_decl); levels = TMPL_ARGS_DEPTH (args); @@ -13370,7 +13366,9 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl) tree orig_arg = TREE_VEC_ELT (t, i); tree new_arg; - if (TREE_CODE (orig_arg) == TREE_VEC) + if (!orig_arg) + new_arg = NULL_TREE; + else if (TREE_CODE (orig_arg) == TREE_VEC) new_arg = tsubst_template_args (orig_arg, args, complain, in_decl); else if (PACK_EXPANSION_P (orig_arg)) { @@ -13420,8 +13418,9 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl) } for (i = 0, out = 0; i < len; i++) { - if ((PACK_EXPANSION_P (TREE_VEC_ELT (orig_t, i)) - || ARGUMENT_PACK_P (TREE_VEC_ELT (orig_t, i))) + tree orig_arg = TREE_VEC_ELT (orig_t, i); + if (orig_arg + && (PACK_EXPANSION_P (orig_arg) || ARGUMENT_PACK_P (orig_arg)) && TREE_CODE (elts[i]) == TREE_VEC) { int idx; @@ -18449,7 +18448,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl, IF_STMT_CONSTEXPR_P (stmt) = IF_STMT_CONSTEXPR_P (t); IF_STMT_CONSTEVAL_P (stmt) = IF_STMT_CONSTEVAL_P (t); if (IF_STMT_CONSTEXPR_P (t)) - args = add_extra_args (IF_STMT_EXTRA_ARGS (t), args); + args = add_extra_args (IF_STMT_EXTRA_ARGS (t), args, complain, in_decl); tmp = RECUR (IF_COND (t)); tmp = finish_if_stmt_cond (tmp, stmt); if (IF_STMT_CONSTEXPR_P (t) diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C new file mode 100644 index 00000000000..824d23431f0 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C @@ -0,0 +1,18 @@ +// PR c++/101181 +// { dg-do compile { target c++20 } } + +template<class T, + bool = requires { typename T::type; }> +struct p { using type = void; }; + +template<class T> +struct p<T, true> { using type = typename T::type; }; + +template<class T> using P = typename p<T>::type; + +using type1 = P<int>; +using type1 = void; + +struct A { using type = char; }; +using type2 = P<A>; +using type2 = char; diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C new file mode 100644 index 00000000000..1113c6f02b9 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C @@ -0,0 +1,22 @@ +// PR c++/101181 +// { dg-do compile { target c++20 } } + +template<class T, + bool = [] () -> bool { + if constexpr (requires { typename T::type; }) + return true; + return false; + }()> +struct p { using type = void; }; + +template<class T> +struct p<T, true> { using type = typename T::type; }; + +template<class T> using P = typename p<T>::type; + +using type1 = P<int>; +using type = void; + +struct A { using type = char; }; +using type2 = P<A>; +using type2 = char; -- 2.32.0.93.g670b81a890