1dabbfb0f4
We represent deduction guides with FUNCTION_DECLs, but they are built
without DECL_CONTEXT, leading to an ICE in type_dependent_expression_p
on the assert that the type of a function template with no dependent
(innermost!) template arguments must be non-dependent. Consider the
attached class-deduction79.C: we create a deduction guide:
template<class T> G(T)-> E<Z>::G<T>
we deduce T and create a partial instantiation:
G(T) -> E<Z>::G<T> [with T = int]
And then do_class_deduction wants to create a CALL_EXPR from the above
using build_new_function_call -> build_over_call which calls mark_used
-> maybe_instantiate_noexcept -> type_dependent_expression_p.
There, the innermost template arguments are non-dependent (<int>), but
the fntype is dependent -- the return type is a TYPENAME_TYPE, and
since we have no DECL_CONTEXT, this check holds:
/* Otherwise, if the function decl isn't from a dependent scope, it can't be
type-dependent. Checking this is important for functions with auto return
type, which looks like a dependent type. */
if (TREE_CODE (expression) == FUNCTION_DECL
&& !(DECL_CLASS_SCOPE_P (expression)
&& dependent_type_p (DECL_CONTEXT (expression)))
whereupon we ICE.
This patch fixes it by deferring the class deduction until the
enclosing scope is non-dependent. build_deduction_guide and maybe_aggr_guide
needed a little tweaking to make the deduction work in a member
template.
Co-Authored-By: Jason Merrill <jason@redhat.com>
gcc/cp/ChangeLog:
PR c++/97034
PR c++/99009
* pt.c (build_deduction_guide): Use INNERMOST_TEMPLATE_ARGS.
(maybe_aggr_guide): Use the original template type where needed. In
a class member template, partially instantiate the result of
collect_ctor_idx_types.
(do_class_deduction): Defer the deduction until the enclosing
scope is non-dependent.
gcc/testsuite/ChangeLog:
PR c++/97034
PR c++/99009
* g++.dg/cpp1z/class-deduction81.C: New test.
* g++.dg/cpp1z/class-deduction82.C: New test.
* g++.dg/cpp2a/class-deduction-aggr8.C: New test.
* g++.dg/cpp2a/class-deduction-aggr9.C: New test.
* g++.dg/cpp2a/class-deduction-aggr10.C: New test.
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