SERVER-32300 Aggregation shell helper should not modify options document

jstests/aggregation/bugs/explain_options_helper.js

@@ -0,0 +1,24 @@
+// Test that the explain helper does not modify the options document passed to it.
+// This test was designed to reproduce SERVER-32300".
+
+(function() {
+    "use strict";
+
+    const coll = db.explain_options;
+    coll.drop();
+
+    for (let i = 0; i < 10; ++i) {
+        assert.writeOK(coll.insert({_id: i}));
+    }
+
+    const collation = {collation: {locale: "zh", backwards: false}};
+
+    const firstResults = coll.aggregate([{$sort: {_id: 1}}], collation).toArray();
+    // Issue an explain in order to verify that 'collation' is not modified to include the explain
+    // flag.
+    assert.commandWorked(coll.explain().aggregate([], collation));
+
+    const secondResults = coll.aggregate([{$sort: {_id: 1}}], collation).toArray();
+    // Assert that the result didn't change after an explain helper is issued.
+    assert.eq(firstResults, secondResults);
+}());

src/mongo/shell/explainable.js

@@ -100,22 +100,22 @@ var Explainable = (function() {
             }
 
             // Add the explain option.
-            extraOpts = extraOpts || {};
+            let extraOptsCopy = Object.extend({}, (extraOpts || {}));
 
             // For compatibility with 3.4 and older versions, when the verbosity is "queryPlanner",
             // we use the explain option to the aggregate command. Otherwise we issue an explain
             // command wrapping the agg command, which is supported by newer versions of the server.
             if (this._verbosity === "queryPlanner") {
-                extraOpts.explain = true;
-                return this._collection.aggregate(pipeline, extraOpts);
+                extraOptsCopy.explain = true;
+                return this._collection.aggregate(pipeline, extraOptsCopy);
             } else {
                 // The aggregate command requires a cursor field.
-                if (!extraOpts.hasOwnProperty("cursor")) {
-                    extraOpts = Object.extend(extraOpts, {cursor: {}});
+                if (!extraOptsCopy.hasOwnProperty("cursor")) {
+                    extraOptsCopy = Object.extend(extraOptsCopy, {cursor: {}});
                 }
 
                 let aggCmd = Object.extend(
-                    {"aggregate": this._collection.getName(), "pipeline": pipeline}, extraOpts);
+                    {"aggregate": this._collection.getName(), "pipeline": pipeline}, extraOptsCopy);
                 let explainCmd = {"explain": aggCmd, "verbosity": this._verbosity};
                 let explainResult = this._collection.runReadCommand(explainCmd);
                 return throwOrReturn(explainResult);