c++: Don't assume trait funcs return error_mark_node when tf_error is passed [PR121291]

For the sake of determining if there are other errors in user code to
report early, many trait functions don't always return error_mark_node
if not called in a SFINAE context (i.e., tf_error is set).  This patch
removes some assumptions on this behaviour I'd made when improving
diagnostics of builtin traits.

	PR c++/121291

gcc/cp/ChangeLog:

	* constraint.cc (diagnose_trait_expr): Remove assumption about
	failures returning error_mark_node.
	* except.cc (explain_not_noexcept): Allow expr not being
	noexcept.
	* method.cc (build_invoke): Adjust comment.
	(is_trivially_xible): Always note non-trivial components if expr
	is not null or error_mark_node.
	(is_nothrow_xible): Likewise for non-noexcept components.
	(is_nothrow_convertible): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/is_invocable7.C: New test.
	* g++.dg/ext/is_nothrow_convertible5.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>

0 files changed, 0 insertions, 0 deletions