c++: NTTP object wrapper substitution fixes [PR103346, ...]

This patch fixes some issues with substitution into a C++20 template
parameter object wrapper:

* The first testcase demonstrates a situation where the same_type_p
  assert in relevant case of tsubst_copy doesn't hold, because (partial)
  substitution of {int,} into the wrapper's TREE_TYPE yields A<int> but
  substitution into the underlying TEMPLATE_PARM_INDEX is a nop due to
  tsubst's level==1/tf_partial early exit tests, hence TREE_TYPE in the
  latter case remains A<T>.  So this patch just gets rid of the assert;
  the type mismatch doesn't seem to be a problem in practice.

* In the second testcase, dependent substitution into the underlying
  TEMPLATE_PARM_INDEX yields a CALL_EXPR with empty TREE_TYPE, which
  tsubst_copy doesn't expect.  This patch fixes this by handling empty
  TREE_TYPE the same way as a non-const TREE_TYPE.  Moreover, after
  this substitution we're left with a VIEW_CONVERT_EXPR wrapping a
  CALL_EXPR instead of a TEMPLATE_PARM_INDEX, which during the subsequent
  non-dependent substitution tsubst_copy doesn't expect either.  So
  this patch also relaxes tsubst_copy to accept such VIEW_CONVERT_EXPR
  too.

* In the third testcase, we end up never resolving the call to
  f.modify() because tsubst_copy doesn't do overload resolution.
  This patch fixes this by moving the handling of these
  VIEW_CONVERT_EXPR wrappers from tsubst_copy to tsubst_copy_and_build.
  For good measure tsubst_copy_and_build should also handle
  REF_PARENTHESIZED_P wrappers instead of delegating to tsubst_copy.

	PR c++/103346
	PR c++/104278
	PR c++/102553

gcc/cp/ChangeLog:

	* pt.cc (tsubst_copy) <case VIEW_CONVERT_EXPR>: Move the
	handling of C++20 template parameter object wrappers to ...
	(tsubst_copy_and_build) <case VIEW_CONVERT_EXPR>: ... here.
	Accept non-TEMPLATE_PARM_INDEX inner operand.  Handle empty
	TREE_TYPE on substituted inner operand.  Remove same_type_p
	assert.  Also handle REF_PARENTHESIZED_P VIEW_CONVERT_EXPRs.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/nontype-class52a.C: New test.
	* g++.dg/cpp2a/nontype-class53.C: New test.
	* g++.dg/cpp2a/nontype-class54.C: New test.
	* g++.dg/cpp2a/nontype-class55.C: New test.

0 files changed, 0 insertions, 0 deletions