[PATCH] PR libstdc++/85965 delay static assertions until types are complete

[Jonathan Wakely <jwakely at redhat dot com>]

The static assertions added for PR libstdc++/48101 were at class scope
and so were evaluated too eagerly, when it might not be possible to
determine whether the function objects are invocable with the key types.
The problematic cases are where the key type is not known to be
convertible to the argument type(s) of the function object until later,
after a type has been completed. Specifically, if the key type is a
pointer to a derived class and the function object's argument type is a
pointer to a base class, then the derived-to-base conversion is only
valid once the derived type is complete.

By moving the static assertions to the destructor they will only be
evaluated when the destructor is instantiated, at which point whether
the key type can be passed to the function object should be knowable.
The ideal place to do the checks would be only when the function objects
are actually invoked, but that would mean adding the checks in numerous
places, so the destructor is used instead.

The tests need to be adjusted because the "required from here" line is
now the location of the destructor, not the point of instantiation in
the test file. For the map and multimap tests which check two
specializations, the dg-error matching the assertion text matches both
cases. Also check the diagnostic output for the template arguments, to
ensure both specializations trigger the assertion.

	PR libstdc++/85965
	* include/bits/hashtable.h (_Hashtable): Move static assertions to
	destructor so they are not evaluated until the _Key type is complete.
	* include/bits/stl_tree.h (_Rb_tree): Likewise.
	* testsuite/23_containers/set/85965.cc: New test.
	* testsuite/23_containers/unordered_set/85965.cc: New test.
	* testsuite/23_containers/map/48101_neg.cc: Replace "here" errors
	with regexp matching the corresponding _Rb_tree specialization.
	* testsuite/23_containers/multimap/48101_neg.cc: Likewise.
	* testsuite/23_containers/multiset/48101_neg.cc: Remove "here" error.
	* testsuite/23_containers/set/48101_neg.cc: Likewise.
	* testsuite/23_containers/unordered_map/48101_neg.cc: Likewise.
	* testsuite/23_containers/unordered_multimap/48101_neg.cc: Likewise.
	* testsuite/23_containers/unordered_multiset/48101_neg.cc: Likewise.
	* testsuite/23_containers/unordered_set/48101_neg.cc: Likewise.

Tested powerpc64le-linux, committed to trunk.

Backport for gcc-8-branch to follow.

Attachment: patch.txt
Description: Text document