On Mon, 14 Feb 2022, Patrick Palka wrote:
> Here the template context for the atomic constraint has two levels of
> template arguments, but since it depends only on the innermost argument
> T we use a single-level argument vector during substitution into the
> constraint (built by get_mapped_args). We eventually pass this vector
> to do_auto_deduction as part of checking the return-type-requirement
> inside the atom, but do_auto_deduction expects outer_targs to be a full
> set of arguments for sake of satisfaction.
>
> do_auto_deduction has a workaround in place to compensate for callers
> that pass only the innermost arguments as outer_targs, but here we're
> passing the _outermost_ arguments. Since the former situation should
> now (after r12-7101) only occur with adc_unify callers and the latter
Whoops, this should be r12-6919 (after which we pass outer_targs
appropriately during adc_variable_type deduction of non-function-scope
variables), not r12-7101, sorry about that.
> only with adc_requirement callers, this patch conditions the existing
> workaround according to the auto_deduction_context: if the context is
> adc_requirement, we add dummy innermost levels, otherwise we add dummy
> outermost levels as before and also assert that the context is adc_unify.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu and tested on cmcstl2
> and range-v3, does this look OK for trunk?
>
> PR c++/104527
>
> gcc/cp/ChangeLog:
>
> * pt.cc (do_auto_deduction): When template argument levels are
> missing from outer_targs, fill in the innermost rather than the
> outermost levels with dummy args if the context is
> adc_requirement, otherwise also assert that the context is
> adc_unify.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-return-req4.C: New test.
> ---
> gcc/cp/pt.cc | 28 +++++++++++++------
> .../g++.dg/cpp2a/concepts-return-req4.C | 24 ++++++++++++++++
> 2 files changed, 44 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-return-req4.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 1b18e2a7787..4ff2710b8ba 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -30215,20 +30215,32 @@ do_auto_deduction (tree type, tree init, tree
> auto_node,
>
> tree full_targs = add_to_template_args (outer_targs, targs);
>
> - /* HACK: Compensate for callers not always communicating all levels of
> - outer template arguments by filling in the outermost missing levels
> - with dummy levels before checking satisfaction. We'll still crash
> - if the constraint depends on a template argument belonging to one of
> - these missing levels, but this hack otherwise allows us to handle a
> - large subset of possible constraints (including all non-dependent
> - constraints). */
> if (int missing_levels = (TEMPLATE_TYPE_ORIG_LEVEL (auto_node)
> - TMPL_ARGS_DEPTH (full_targs)))
> {
> tree dummy_levels = make_tree_vec (missing_levels);
> for (int i = 0; i < missing_levels; ++i)
> TREE_VEC_ELT (dummy_levels, i) = make_tree_vec (0);
> - full_targs = add_to_template_args (dummy_levels, full_targs);
> + if (context == adc_requirement)
> + /* We're checking a requires-expr's return-type-requirement that's
> + part of an atomic constraint that doesn't depend on any innermost
> + template arguments, so OUTER_TARGS (built by get_mapped_args) is
> + missing at least one innermost level. Fill in the innermost
> + levels of OUTER_TARGS with dummy levels. */
> + full_targs = add_to_template_args
> + (add_to_template_args (outer_targs, dummy_levels), targs);
> + else
> + {
> + /* Otherwise, fill in the _outermost_ levels with dummy levels.
> + This compensates for adc_unify callers that only pass the
> + innermost level of template arguments as OUTER_TARGS. We'll
> + still crash if the constraint depends on a template argument
> + belonging to one of these missing levels, but this hack
> + otherwise allows us to handle a large subset of possible
> + constraints (including all non-dependent constraints). */
> + gcc_checking_assert (context == adc_unify);
> + full_targs = add_to_template_args (dummy_levels, full_targs);
> + }
> }
>
> if (!constraints_satisfied_p (auto_node, full_targs))
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-return-req4.C
> b/gcc/testsuite/g++.dg/cpp2a/concepts-return-req4.C
> new file mode 100644
> index 00000000000..471946bc8eb
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-return-req4.C
> @@ -0,0 +1,24 @@
> +// PR c++/104527
> +// { dg-do compile { target c++20 } }
> +
> +template<class T, class U>
> +concept is_same = __is_same(T, U);
> +
> +template<class T>
> +struct A {
> + template<class...>
> + requires requires { { 0 } -> is_same<T>; }
> + struct B {};
> +
> + template<class...>
> + requires requires { { 1 } -> is_same<T>; }
> + static void f();
> +};
> +
> +A<int>::B<> a1;
> +A<bool>::B<> a2; // { dg-error "constraint" }
> +
> +int main() {
> + A<int>::f();
> + A<bool>::f(); // { dg-error "no match" }
> +}
> --
> 2.35.1.102.g2b9c120970
>
>
