c++: overload sets and placeholder return type [PR64194]
authorPatrick Palka <ppalka@redhat.com>
Thu, 30 Jul 2020 02:06:44 +0000 (22:06 -0400)
committerPatrick Palka <ppalka@redhat.com>
Thu, 30 Jul 2020 02:06:44 +0000 (22:06 -0400)
commit2c58f5cadfac338a67723fd6e41c9097760c4a33
tree5a10e90b44cbed1580f27667e45b3fcafb165fff
parent71141b1bd537cc516e485c834c2d36abba3f4544
c++: overload sets and placeholder return type [PR64194]

In the testcase below, template argument deduction for the call
g(id<int>) goes wrong because the functions in the overload set id<int>
each have a yet-undeduced auto return type, and this undeduced return
type makes try_one_overload fail to match up any of the overloads with
g's parameter type, leading to g's template argument going undeduced and
to the overload set going unresolved.

This patch fixes this issue by performing return type deduction via
instantiation before doing try_one_overload, in a manner similar to what
resolve_address_of_overloaded_function does.

gcc/cp/ChangeLog:

PR c++/64194
* pt.c (resolve_overloaded_unification): If the function
template specialization has a placeholder return type,
then instantiate it before attempting unification.

gcc/testsuite/ChangeLog:

PR c++/64194
* g++.dg/cpp1y/auto-fn60.C: New test.
gcc/cp/pt.c
gcc/testsuite/g++.dg/cpp1y/auto-fn60.C [new file with mode: 0644]