On Thu, 15 Dec 2022, Jason Merrill wrote: > On 12/15/22 14:31, Patrick Palka wrote: > > On Thu, 15 Dec 2022, Patrick Palka wrote: > > > > > On Thu, 15 Dec 2022, Jason Merrill wrote: > > > > > > > On 12/12/22 12:20, Patrick Palka wrote: > > > > > When instantiating a constrained hidden template friend, we need to > > > > > substitute into its constraints for sake of declaration matching. > > > > > > > > Hmm, we shouldn't need to do declaration matching when there's only a > > > > single > > > > declaration. > > > > > > Oops, indeed. It looks like in this case we're not calling > > > maybe_substitute_reqs_for during declaration matching, but rather from > > > tsubst_friend_function and specifically for the non-trailing requirements: > > > > > > if (TREE_CODE (new_friend) == TEMPLATE_DECL) > > > { > > > DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P (new_friend) = false; > > > DECL_USE_TEMPLATE (DECL_TEMPLATE_RESULT (new_friend)) = 0; > > > DECL_SAVED_TREE (DECL_TEMPLATE_RESULT (new_friend)) > > > = DECL_SAVED_TREE (DECL_TEMPLATE_RESULT (decl)); > > > > > > /* Substitute TEMPLATE_PARMS_CONSTRAINTS so that parameter levels > > > will > > > match in decls_match. */ > > > tree parms = DECL_TEMPLATE_PARMS (new_friend); > > > tree treqs = TEMPLATE_PARMS_CONSTRAINTS (parms); > > > treqs = maybe_substitute_reqs_for (treqs, new_friend); > > > if (treqs != TEMPLATE_PARMS_CONSTRAINTS (parms)) > > > { > > > TEMPLATE_PARMS_CONSTRAINTS (parms) = treqs; > > > /* As well as each TEMPLATE_PARM_CONSTRAINTS. */ > > > tsubst_each_template_parm_constraints (parms, args, > > > tf_warning_or_error); > > > } > > > } > > > > > > I'll adjust the commit message appropriately. > > > > > > > > > > > > For > > > > > this substitution we use a full argument vector whose outer levels > > > > > correspond to the class's arguments and innermost level corresponds to > > > > > the template's level-lowered generic arguments. > > > > > > > > > > But for A<int>::f here, for which the relevant argument vector is > > > > > {{int}, {Us...}}, this substitution triggers the assert in > > > > > use_pack_expansion_extra_args_p since one argument is a pack expansion > > > > > and the other isn't. > > > > > > > > > > And for A<int, int>::f, for which the relevant argument vector is > > > > > {{int, int}, {Us...}}, the use_pack_expansion_extra_args_p assert > > > > > would > > > > > also trigger but we first get a bogus "mismatched argument pack > > > > > lengths" > > > > > error from tsubst_pack_expansion. > > > > > > > > > > These might ultimately be bugs in tsubst_pack_expansion, but it seems > > > > > we can work around them by tweaking the constraint substitution in > > > > > maybe_substitute_reqs_for to only use the friend's outer arguments in > > > > > the case of a template friend. > > > > > > > > Yes, this is how we normally substitute a member template during class > > > > instantiation: with the class' template args, not its own. The assert > > > > seems > > > > to be enforcing that. > > > > > > Ah, makes snese. > > > > > > > > > > > > This should be otherwise equivalent to > > > > > substituting using the full arguments, since the template's innermost > > > > > arguments are just its generic arguments with level=1. > > > > > > > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK > > > > > for > > > > > trunk/12? > > > > > > > > > > PR c++/108066 > > > > > PR c++/108067 > > > > > > > > > > gcc/cp/ChangeLog: > > > > > > > > > > * constraint.cc (maybe_substitute_reqs_for): For a template > > > > > friend, substitute using only its outer arguments. Remove > > > > > dead uses_template_parms test. > > > > > > > > I don't see any removal? > > > > > > Oops, I reverted that change before posting the patch but forgot to adjust > > > the > > > ChangeLog as well. Removing the uses_template_parms test seems to be safe > > > but > > > it's not necessary to fix the bug. > > > > > > > > > > > > gcc/testsuite/ChangeLog: > > > > > > > > > > * g++.dg/cpp2a/concepts-friend12.C: New test. > > > > > --- > > > > > gcc/cp/constraint.cc | 8 +++++++ > > > > > .../g++.dg/cpp2a/concepts-friend12.C | 22 > > > > > +++++++++++++++++++ > > > > > 2 files changed, 30 insertions(+) > > > > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend12.C > > > > > > > > > > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc > > > > > index d4cd92ec3b4..f9d1009c9fe 100644 > > > > > --- a/gcc/cp/constraint.cc > > > > > +++ b/gcc/cp/constraint.cc > > > > > @@ -1352,6 +1352,14 @@ maybe_substitute_reqs_for (tree reqs, > > > > > const_tree > > > > > decl) > > > > > tree tmpl = DECL_TI_TEMPLATE (decl); > > > > > tree gargs = generic_targs_for (tmpl); > > > > > processing_template_decl_sentinel s; > > > > > + if (PRIMARY_TEMPLATE_P (tmpl)) > > > > > + { > > > > > + if (TEMPLATE_ARGS_DEPTH (gargs) == 1) > > > > > + return reqs; > > > > > + ++processing_template_decl; > > > > > + gargs = copy_node (gargs); > > > > > + --TREE_VEC_LENGTH (gargs); > > > > > > > > Maybe instead of messing with TEMPLATE_ARGS_DEPTH we want to grab the > > > > targs > > > > for DECL_FRIEND_CONTEXT instead of decl itself? > > > > > > IIUC DECL_FRIEND_CONTEXT wouldn't give us the right args if the template > > > friend > > > is declared inside a partial specialization: > > > > > > template<class T, class U> > > > concept C = __is_same(T, U); > > > > > > template<class T> > > > struct A; > > > > > > template<class T> > > > struct A<T*> { > > > template<class U> > > > requires (__is_same(T, U)) > > > friend void f() { }; > > > }; > > > > > > template struct A<int*>; > > > > > > The DECL_FRIEND_CONTEXT of f is A<int*>, whose TYPE_TI_ARGS are {int*}, > > > relative to the primary template instead of the partial specialization. > > > So > > > we'd wrongly end up substituting T=int* instead of T=int into f's > > > TEMPLATE_PARMS_CONSTRAINTS. > > > > > > r12-6950-g76dc465aaf1b74 fixed a similar issue when substituting into > > > class-scope deduction guides declared inside a partial specialization. > > Ah, so this is a workaround for not being able to get at the template args > used in substituting A<int*> from A<int*> itself. > > Maybe factor this out from here and ctor_deduction_guides_for into an > outer_template_args function with a comment to that effect?
Like so? Bootstrapped and regtested on x86_64-pc-linux-gnu. > > Maybe it would make sense to update CLASSTYPE_TEMPLATE_INFO for A<int*> after > we choose a partial specialization in instantiate_class_template, but I'm sure > a bunch of places would need to be adjusted to handle that. *nod* Having that information readily available instead of having to call most_specialized_partial_spec would be nice. -- >8 -- Subject: [PATCH] c++: template friend with variadic constraints [PR107853] PR c++/107853 gcc/cp/ChangeLog: * constraint.cc (maybe_substitute_reqs_for): For a template friend, substitute using only its outer arguments via outer_template_args. * cp-tree.h (outer_template_args): Declare. * pt.cc (outer_template_args): Define, factored out and generalized from ... (ctor_deduction_guides_for): ... here. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-friend12.C: New test. * g++.dg/cpp2a/concepts-friend13.C: New test. --- gcc/cp/constraint.cc | 7 ++-- gcc/cp/cp-tree.h | 1 + gcc/cp/pt.cc | 35 +++++++++++++------ .../g++.dg/cpp2a/concepts-friend12.C | 21 +++++++++++ .../g++.dg/cpp2a/concepts-friend13.C | 20 +++++++++++ 5 files changed, 71 insertions(+), 13 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend12.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend13.C diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc index 37eae03afdb..247a8278d40 100644 --- a/gcc/cp/constraint.cc +++ b/gcc/cp/constraint.cc @@ -1350,11 +1350,12 @@ maybe_substitute_reqs_for (tree reqs, const_tree decl) if (DECL_UNIQUE_FRIEND_P (decl) && DECL_TEMPLATE_INFO (decl)) { tree tmpl = DECL_TI_TEMPLATE (decl); - tree gargs = generic_targs_for (tmpl); + tree outer_args = outer_template_args (tmpl); processing_template_decl_sentinel s; - if (uses_template_parms (gargs)) + if (PRIMARY_TEMPLATE_P (tmpl) + || uses_template_parms (outer_args)) ++processing_template_decl; - reqs = tsubst_constraint (reqs, gargs, + reqs = tsubst_constraint (reqs, outer_args, tf_warning_or_error, NULL_TREE); } return reqs; diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 541d760492d..1f4967c2ba0 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -7056,6 +7056,7 @@ extern tree maybe_set_retval_sentinel (void); extern tree template_parms_to_args (tree); extern tree template_parms_level_to_args (tree); extern tree generic_targs_for (tree); +extern tree outer_template_args (tree); /* in expr.cc */ extern tree cplus_expand_constant (tree); diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index e68c74913f5..c0593e9cac6 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -4958,6 +4958,29 @@ generic_targs_for (tree tmpl) return template_parms_to_args (DECL_TEMPLATE_PARMS (tmpl)); } +/* Return the template arguments corresponding to the template + parameters of TMPL's enclosing scope. When TMPL is a member + template of a partial specialization, this returns the arguments + for the partial specialization as opposed to those for the primary + template, which is the main difference between this function and + simply inspecting e.g. the TYPE_TI_ARGS of TMPL's DECL_CONTEXT. */ + +tree +outer_template_args (tree tmpl) +{ + tree ti = get_template_info (DECL_TEMPLATE_RESULT (tmpl)); + if (!ti) + return NULL_TREE; + tree args = TI_ARGS (ti); + if (!PRIMARY_TEMPLATE_P (tmpl)) + return args; + if (TMPL_ARGS_DEPTH (args) == 1) + return NULL_TREE; + args = copy_node (args); + --TREE_VEC_LENGTH (args); + return args; +} + /* Update the declared TYPE by doing any lookups which were thought to be dependent, but are not now that we know the SCOPE of the declarator. */ @@ -30081,16 +30104,8 @@ alias_ctad_tweaks (tree tmpl, tree uguides) static tree ctor_deduction_guides_for (tree tmpl, tsubst_flags_t complain) { - tree type = TREE_TYPE (tmpl); - tree outer_args = NULL_TREE; - if (DECL_CLASS_SCOPE_P (tmpl) - && CLASSTYPE_TEMPLATE_INSTANTIATION (DECL_CONTEXT (tmpl))) - { - outer_args = copy_node (CLASSTYPE_TI_ARGS (type)); - gcc_assert (TMPL_ARGS_DEPTH (outer_args) > 1); - --TREE_VEC_LENGTH (outer_args); - type = TREE_TYPE (most_general_template (tmpl)); - } + tree outer_args = outer_template_args (tmpl); + tree type = TREE_TYPE (most_general_template (tmpl)); tree cands = NULL_TREE; diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend12.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend12.C new file mode 100644 index 00000000000..9687be5931a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend12.C @@ -0,0 +1,21 @@ +// PR c++/107853 +// { dg-do compile { target c++20 } } + +template<class T, class U> +concept C = __is_same(T, U); + +template<class... Ts> +struct A { + template<class... Us> + requires (C<Ts, Us> && ...) + friend void f(A, A<Us...>) { } +}; + +int main() { + A<int> x; + f(x, x); + A<int, int> y; + f(y, y); + A<char> z; + f(x, z); // { dg-error "no match" } +} diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend13.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend13.C new file mode 100644 index 00000000000..3cc4505a7ef --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend13.C @@ -0,0 +1,20 @@ +// Verify we substitute the correct outer template arguments +// when instantiating a constrained template friend declared +// inside a partial specialization. +// { dg-do compile { target c++20 } } + +template<class U> + requires __is_same(int*, U) +void f() { }; + +template<class T> +struct A; + +template<class T> +struct A<T*> { + template<class U> + requires __is_same(T, U) + friend void f() { } // { dg-bogus "redefinition" } +}; + +template struct A<int*>; -- 2.39.0.95.g7c2ef319c5