Major - P3 The count command does not respect the user-specified hint, if an empty query predicate is specified.
This is due to a bug in CountStage::work(), which fails to check for a non-empty hint before deciding to apply the "trivial count" optimization.
Reproduce as follows:
> db.foo.drop() true > db.foo.ensureIndex({a: 1}, {sparse: true}) { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.foo.insert({}) WriteResult({ "nInserted" : 1 }) > db.foo.find().hint({a: 1}).itcount() 0 > db.foo.find().hint({a: 1}).count() 1 // Unexpected: should return 0 instead. >