INFRA-3688 Support hidden index flag (globalsign#32)

Author: cgorbit

session.go

@@ -1448,6 +1448,7 @@ type indexSpec struct {
 	LanguageOverride        string  `bson:"language_override,omitempty"`
 	TextIndexVersion        int     `bson:"textIndexVersion,omitempty"`
 	PartialFilterExpression bson.M  `bson:"partialFilterExpression,omitempty"`
+	Hidden                  bool    `bson:"hidden,omitempty"`
 
 	Collation *Collation `bson:"collation,omitempty"`
 }
@@ -1473,6 +1474,9 @@ type Index struct {
 	// computed by EnsureIndex based on the index key.
 	Name string
 
+	// Whether index is hidden from query planner
+	Hidden bool
+
 	// Properties for spatial indexes.
 	//
 	// Min and Max were improperly typed as int when they should have been
@@ -1750,6 +1754,7 @@ func (c *Collection) EnsureIndex(index Index) error {
 		LanguageOverride:        index.LanguageOverride,
 		Collation:               index.Collation,
 		PartialFilterExpression: index.PartialFilter,
+		Hidden:                  index.Hidden,
 	}
 
 	if spec.Min == 0 && spec.Max == 0 {
@@ -1976,6 +1981,7 @@ func indexFromSpec(spec indexSpec) Index {
 		ExpireAfter:      time.Duration(spec.ExpireAfter) * time.Second,
 		Collation:        spec.Collation,
 		PartialFilter:    spec.PartialFilterExpression,
+		Hidden:           spec.Hidden,
 	}
 	if float64(int(spec.Min)) == spec.Min && float64(int(spec.Max)) == spec.Max {
 		index.Min = int(spec.Min)