[PATCH] Fix filesystem::path for iterators with const value_type

[Jonathan Wakely <jwakely at redhat dot com>]

For some reason the Filesystem library says that you can construct
paths from iterators with value_type that is a possibly const encoded
character type. I don't know why we support const value_type in this
place, when normally that is bogus (even const_iterators have a
non-const value_type, and various algorithms won't compile with const
value_type).

Anyway, this fixes path to allow such wonky iterators, and fixes a bug
where I was using *iter++ which isn't defined for input iterators.

	* include/experimental/bits/fs_path.h
	(path::_S_convert<_Iter>(_Iter, _Iter)): Remove cv-qualifiers from
	iterator's value_type.
	(path::_S_convert<_Iter>(_Iter __first, __null_terminated)): Likewise.
	Do not use operation not supported by input iterators.
	(path::__is_path_iter_src): Add partial specialization for const
	encoded character types.
	* testsuite/experimental/filesystem/path/construct/range.cc: Test
	construction from input iterators with const value types.

Tested powerpc64le-linux, committed to trunk.

Attachment: patch.txt
Description: Text document