1 files changed, 28 insertions, 5 deletions

diff --git a/src/mongo/db/query/projection_policies.h b/src/mongo/db/query/projection_policies.h
index 09094227c86..1e9214f2515 100644
--- a/src/mongo/db/query/projection_policies.h
+++ b/src/mongo/db/query/projection_policies.h
@@ -55,6 +55,9 @@ struct ProjectionPolicies {
     // Whether $elemMatch, find() $slice and positional projection are allowed.
     enum class FindOnlyFeaturesPolicy { kBanFindOnlyFeatures, kAllowFindOnlyFeatures };
 
+    // Whether the empty projection, {}, is permitted.
+    enum class EmptyProjectionPolicy { kBanEmptyProjection, kAllowEmptyProjection };
+
     static const DefaultIdPolicy kDefaultIdPolicyDefault = DefaultIdPolicy::kIncludeId;
     static const ArrayRecursionPolicy kArrayRecursionPolicyDefault =
         ArrayRecursionPolicy::kRecurseNestedArrays;
@@ -62,46 +65,66 @@ struct ProjectionPolicies {
         ComputedFieldsPolicy::kAllowComputedFields;
     static const FindOnlyFeaturesPolicy kFindOnlyFeaturesPolicyDefault =
         FindOnlyFeaturesPolicy::kBanFindOnlyFeatures;
+    static const EmptyProjectionPolicy kEmptyProjectionPolicyDefault =
+        EmptyProjectionPolicy::kBanEmptyProjection;
 
     static ProjectionPolicies findProjectionPolicies() {
         return ProjectionPolicies{kDefaultIdPolicyDefault,
                                   kArrayRecursionPolicyDefault,
                                   kComputedFieldsPolicyDefault,
-                                  FindOnlyFeaturesPolicy::kAllowFindOnlyFeatures};
+                                  FindOnlyFeaturesPolicy::kAllowFindOnlyFeatures,
+                                  EmptyProjectionPolicy::kAllowEmptyProjection};
     }
 
     static ProjectionPolicies aggregateProjectionPolicies() {
         return ProjectionPolicies{kDefaultIdPolicyDefault,
                                   kArrayRecursionPolicyDefault,
                                   kComputedFieldsPolicyDefault,
-                                  FindOnlyFeaturesPolicy::kBanFindOnlyFeatures};
+                                  FindOnlyFeaturesPolicy::kBanFindOnlyFeatures,
+                                  kEmptyProjectionPolicyDefault};
     }
 
     static ProjectionPolicies wildcardIndexSpecProjectionPolicies() {
         return ProjectionPolicies{DefaultIdPolicy::kExcludeId,
                                   ArrayRecursionPolicy::kDoNotRecurseNestedArrays,
                                   ComputedFieldsPolicy::kBanComputedFields,
-                                  FindOnlyFeaturesPolicy::kBanFindOnlyFeatures};
+                                  FindOnlyFeaturesPolicy::kBanFindOnlyFeatures,
+                                  kEmptyProjectionPolicyDefault};
+    }
+
+    static ProjectionPolicies columnStoreIndexSpecProjectionPolicies() {
+        return ProjectionPolicies{kDefaultIdPolicyDefault,
+                                  ArrayRecursionPolicy::kDoNotRecurseNestedArrays,
+                                  ComputedFieldsPolicy::kBanComputedFields,
+                                  FindOnlyFeaturesPolicy::kBanFindOnlyFeatures,
+                                  EmptyProjectionPolicy::kAllowEmptyProjection};
     }
 
     ProjectionPolicies(
         DefaultIdPolicy idPolicy = kDefaultIdPolicyDefault,
         ArrayRecursionPolicy arrayRecursionPolicy = kArrayRecursionPolicyDefault,
         ComputedFieldsPolicy computedFieldsPolicy = kComputedFieldsPolicyDefault,
-        FindOnlyFeaturesPolicy findOnlyFeaturesPolicy = kFindOnlyFeaturesPolicyDefault)
+        FindOnlyFeaturesPolicy findOnlyFeaturesPolicy = kFindOnlyFeaturesPolicyDefault,
+        EmptyProjectionPolicy emptyProjectionPolicy = kEmptyProjectionPolicyDefault)
         : idPolicy(idPolicy),
           arrayRecursionPolicy(arrayRecursionPolicy),
           computedFieldsPolicy(computedFieldsPolicy),
-          findOnlyFeaturesPolicy(findOnlyFeaturesPolicy) {}
+          findOnlyFeaturesPolicy(findOnlyFeaturesPolicy),
+          emptyProjectionPolicy(emptyProjectionPolicy) {}
 
     const DefaultIdPolicy idPolicy;
     const ArrayRecursionPolicy arrayRecursionPolicy;
     const ComputedFieldsPolicy computedFieldsPolicy;
     const FindOnlyFeaturesPolicy findOnlyFeaturesPolicy;
+    const EmptyProjectionPolicy emptyProjectionPolicy;
 
     bool findOnlyFeaturesAllowed() const {
         return findOnlyFeaturesPolicy == FindOnlyFeaturesPolicy::kAllowFindOnlyFeatures;
     }
+
+    bool emptyProjectionAllowed() const {
+        return emptyProjectionPolicy == EmptyProjectionPolicy::kAllowEmptyProjection;
+    }
 };
 
 }  // namespace mongo