SERVER-7502 test that partial projection of _id works correctly

2 files changed, 28 insertions, 5 deletions

diff --git a/jstests/aggregation/sources/project/remove_redundant_projects.js b/jstests/aggregation/sources/project/remove_redundant_projects.js
index e4584df4f65..ea620be2c2a 100644
--- a/jstests/aggregation/sources/project/remove_redundant_projects.js
+++ b/jstests/aggregation/sources/project/remove_redundant_projects.js
@@ -140,13 +140,15 @@ assertResultsMatch({
     removedProjectStage: {_id: 0, a: 1}
 });
 
-// Test that projections on _id with nested fields are not removed from pipeline. Due to
-// SERVER-7502, the dependency analysis does not generate a covered projection for nested
-// fields in _id and thus we cannot remove the stage.
+// Test that projections on _id with nested fields are removed from pipeline.
 indexSpec = {
     '_id.a': 1,
     a: 1
 };
-assertResultsMatch(
-    {pipeline: [{$project: {'_id.a': 1}}], expectProjectToCoalesce: false, index: indexSpec});
+assertResultsMatch({
+    pipeline: [{$match: {"_id.a": 1}}, {$project: {'_id.a': 1}}],
+    expectProjectToCoalesce: true,
+    index: indexSpec,
+    pipelineOptimizedAway: true,
+});
 }());
diff --git a/jstests/core/id_partial_projection.js b/jstests/core/id_partial_projection.js
new file mode 100644
index 00000000000..7affbcfb875
--- /dev/null
+++ b/jstests/core/id_partial_projection.js
@@ -0,0 +1,21 @@
+/**
+ * Tests partial inclusion/exclusion of _id.
+ * See SERVER-7502 for details.
+ */
+(function() {
+"use strict";
+
+const coll = db.id_partial_projection;
+coll.drop();
+
+assert.commandWorked(coll.insert({_id: {a: 1, b: 1}, otherField: 1}));
+assert.commandWorked(coll.insert({_id: 3, otherField: 2}));
+
+assert.eq(coll.find({}, {"_id": 1}).toArray(), [{_id: {a: 1, b: 1}}, {_id: 3}]);
+assert.eq(coll.find({}, {"_id.a": 1}).toArray(), [{_id: {a: 1}}, {}]);
+assert.eq(coll.find({}, {"_id.b": 1}).toArray(), [{_id: {b: 1}}, {}]);
+
+assert.eq(coll.find({}, {"_id.a": 0}).toArray(),
+          [{_id: {b: 1}, otherField: 1}, {_id: 3, otherField: 2}]);
+assert.eq(coll.find({}, {_id: 0}).toArray(), [{otherField: 1}, {otherField: 2}]);
+})();