Support additional doc option opts in views

[b20n]

COUCHDB-2568 allowed several attachment-related doc open options to be
passed through _all_docs queries. This patch extends that work to
various other options by adding support for various doc open options to
the view argument parser:

• revs_info
• deleted_conflicts
• meta
• r

Additionally, this patch changes the behavior of the "conflicts" view
option to furthermore apply the "conflicts" doc open option if
include_docs=true is specified by the user.

Without this functionality there is no way for a user to implement an
"always on" conflict detection and resolution policy if they're using
_all_docs POST queries as their primary document access path.

COUCHDB-3064

[chewbranca]

@banjiewen you'll want to add validations for these new arguments in

couchdb-couch-mrview/src/couch_mrview_util.erl

Lines 402 to 522 in 3ce2864

	validate_args(Args) ->
	GroupLevel = determine_group_level(Args),
	Reduce = Args#mrargs.reduce,
	case Reduce == undefined orelse is_boolean(Reduce) of
	true -> ok;
	_ -> mrverror(<<"Invalid `reduce` value.">>)
	end,
	case {Args#mrargs.view_type, Reduce} of
	{map, true} -> mrverror(<<"Reduce is invalid for map-only views.">>);
	_ -> ok
	end,
	case {Args#mrargs.view_type, GroupLevel, Args#mrargs.keys} of
	{red, exact, _} -> ok;
	{red, _, KeyList} when is_list(KeyList) ->
	Msg = <<"Multi-key fetchs for reduce views must use `group=true`">>,
	mrverror(Msg);
	_ -> ok
	end,
	case Args#mrargs.keys of
	Keys when is_list(Keys) -> ok;
	undefined -> ok;
	_ -> mrverror(<<"`keys` must be an array of strings.">>)
	end,
	case {Args#mrargs.keys, Args#mrargs.start_key,
	Args#mrargs.end_key} of
	{undefined, _, _} -> ok;
	{[], _, _} -> ok;
	{[_|_], undefined, undefined} -> ok;
	_ -> mrverror(<<"`keys` is incompatible with `key`"
	", `start_key` and `end_key`">>)
	end,
	case Args#mrargs.start_key_docid of
	undefined -> ok;
	SKDocId0 when is_binary(SKDocId0) -> ok;
	_ -> mrverror(<<"`start_key_docid` must be a string.">>)
	end,
	case Args#mrargs.end_key_docid of
	undefined -> ok;
	EKDocId0 when is_binary(EKDocId0) -> ok;
	_ -> mrverror(<<"`end_key_docid` must be a string.">>)
	end,
	case Args#mrargs.direction of
	fwd -> ok;
	rev -> ok;
	_ -> mrverror(<<"Invalid direction.">>)
	end,
	case {Args#mrargs.limit >= 0, Args#mrargs.limit == undefined} of
	{true, _} -> ok;
	{_, true} -> ok;
	_ -> mrverror(<<"`limit` must be a positive integer.">>)
	end,
	case Args#mrargs.skip < 0 of
	true -> mrverror(<<"`skip` must be >= 0">>);
	_ -> ok
	end,
	case {Args#mrargs.view_type, GroupLevel} of
	{red, exact} -> ok;
	{_, 0} -> ok;
	{red, Int} when is_integer(Int), Int >= 0 -> ok;
	{red, _} -> mrverror(<<"`group_level` must be >= 0">>);
	{map, _} -> mrverror(<<"Invalid use of grouping on a map view.">>)
	end,
	case Args#mrargs.stale of
	ok -> ok;
	update_after -> ok;
	false -> ok;
	_ -> mrverror(<<"Invalid value for `stale`.">>)
	end,
	case is_boolean(Args#mrargs.inclusive_end) of
	true -> ok;
	_ -> mrverror(<<"Invalid value for `inclusive_end`.">>)
	end,
	case {Args#mrargs.view_type, Args#mrargs.include_docs} of
	{red, true} -> mrverror(<<"`include_docs` is invalid for reduce">>);
	{_, ID} when is_boolean(ID) -> ok;
	_ -> mrverror(<<"Invalid value for `include_docs`">>)
	end,
	case {Args#mrargs.view_type, Args#mrargs.conflicts} of
	{_, undefined} -> ok;
	{map, V} when is_boolean(V) -> ok;
	{red, undefined} -> ok;
	{map, _} -> mrverror(<<"Invalid value for `conflicts`.">>);
	{red, _} -> mrverror(<<"`conflicts` is invalid for reduce views.">>)
	end,
	SKDocId = case {Args#mrargs.direction, Args#mrargs.start_key_docid} of
	{fwd, undefined} -> <<>>;
	{rev, undefined} -> <<255>>;
	{_, SKDocId1} -> SKDocId1
	end,
	EKDocId = case {Args#mrargs.direction, Args#mrargs.end_key_docid} of
	{fwd, undefined} -> <<255>>;
	{rev, undefined} -> <<>>;
	{_, EKDocId1} -> EKDocId1
	end,
	case is_boolean(Args#mrargs.sorted) of
	true -> ok;
	_ -> mrverror(<<"Invalid value for `sorted`.">>)
	end,
	Args#mrargs{
	start_key_docid=SKDocId,
	end_key_docid=EKDocId,
	group_level=GroupLevel
	}.

[b20n]

you'll want to add validations for these new arguments

These all end up in #mrargs.doc_options, which isn't validated there. I'm not sure it's validated anywhere, to be honest.