[Bug c++/56377] [4.8 Regression] <missing> template args in substitution-failure diagnostics

[pl.smith.mail at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56377

--- Comment #1 from Paul Smith <pl.smith.mail at gmail dot com> 2013-02-18 16:12:00 UTC ---
Looks like this was introduced in rev. 190664, with the merging of
'deduction_tsubst_fntype' into 'fn_type_unification'.

The instantiation context is constructed with 'targs' as the vector of template
arguments, which is still empty when substituting the explicit arguments into
the function type the first time. This can be fixed by either constructing the
instantiation context using 'explicit_targs' when non-null, or by copying
'explicit_targs' into 'targs' before the substitution.