[C++ Patch/RFC] PR 57092

[Jason Merrill]

On 04/30/2013 11:59 AM, Paolo Carlini wrote:
> Currently, in some cases (see, eg, template/canon-type-9.C) we have that
> id is true and DECLTYPE_TYPE_EXPR (t) is a TEMPLATE_PARM_INDEX but the
> tsubst_copy_and_build call returns a TEMPLATE_PARM_INDEX again, not an
> ADDR_EXPR, not an expression

Good point, this can happen for partial instantiations, when 
processing_template_decl is still true.  We want to keep the 
DECLTYPE_TYPE around until the expression instantiates to something 
non-instantiation-dependent.

Hmm.  Maybe the right answer is to just add a default: case to 
finish_decltype_type and trust that it will be right.

Jason