test@127.0.0.1:27017(4.0.0) > db.partial.ensureIndex({i: 1}, {partialFilterExpression: {dt: {$gte:ISODate("2016-07-12T23:58:24.278Z"),$lt: ISODate("2016-07-12T23:58:33.773Z")}}});
{
	"createdCollectionAutomatically" : false,
	"numIndexesBefore" : 4,
	"numIndexesAfter" : 5,
	"ok" : 1
}
test@127.0.0.1:27017(4.0.0) > db.partial.ensureIndex({i: 1}, {partialFilterExpression: {dt: {$gte:ISODate("2016-07-12T23:58:24.278Z"),$lt: ISODate("2016-07-12T23:58:33.773Z")}},name:"i_1_partial2"})
{
	"createdCollectionAutomatically" : false,
	"numIndexesBefore" : 5,
	"numIndexesAfter" : 5,
	"note" : "all indexes already exist",
	"ok" : 1
}
test@127.0.0.1:27017(4.0.0) > db.partial.ensureIndex({i: 1}, {partialFilterExpression: {dt: {$lt: ISODate("2016-07-12T23:58:33.773Z"), $gte:ISODate("2016-07-12T23:58:24.278Z")}},name:"i_1_partial3"})
{
	"ok" : 0,
	"errmsg" : "Index: { v: 2, key: { i: 1.0 }, name: \"i_1_partial3\", ns: \"test.partial\", partialFilterExpression: { dt: { $lt: new Date(1468367913773), $gte: new Date(1468367904278) } } } already exists with different options: { v: 2, key: { i: 1.0 }, name: \"i_1\", ns: \"test.partial\", partialFilterExpression: { dt: { $gte: new Date(1468367904278), $lt: new Date(1468367913773) } } }",
	"code" : 85,
	"codeName" : "IndexOptionsConflict"
}