fix(aggregate): automatically convert accumulator function options to…

… strings

Fix #9364

lib/aggregate.js

@@ -8,6 +8,7 @@ const AggregationCursor = require('./cursor/AggregationCursor');
 const Query = require('./query');
 const applyGlobalMaxTimeMS = require('./helpers/query/applyGlobalMaxTimeMS');
 const promiseOrCallback = require('./helpers/promiseOrCallback');
+const stringifyAccumulatorOptions = require('./helpers/aggregate/stringifyAccumulatorOptions');
 const util = require('util');
 const utils = require('./utils');
 const read = Query.prototype.read;
@@ -982,8 +983,8 @@ Aggregate.prototype.exec = function(callback) {
   }
 
   return promiseOrCallback(callback, cb => {
-
     prepareDiscriminatorPipeline(this);
+    stringifyAccumulatorOptions(this._pipeline);
 
     model.hooks.execPre('aggregate', this, error => {
       if (error) {

lib/helpers/aggregate/stringifyAccumulatorOptions.js

@@ -0,0 +1,38 @@
+'use strict';
+
+module.exports = function stringifyAccumulatorOptions(pipeline) {
+  if (!Array.isArray(pipeline)) {
+    return;
+  }
+
+  for (const stage of pipeline) {
+    if (stage == null) {
+      continue;
+    }
+
+    const canHaveAccumulator = stage.$group || stage.$bucket || stage.$bucketAuto;
+    if (canHaveAccumulator != null) {
+      for (const key of Object.keys(canHaveAccumulator)) {
+        handleAccumulator(canHaveAccumulator[key]);
+      }
+    }
+
+    if (stage.$facet != null) {
+      for (const key of Object.keys(stage.$facet)) {
+        stringifyAccumulatorOptions(stage.$facet[key]);
+      }
+    }
+  }
+};
+
+function handleAccumulator(operator) {
+  if (operator == null || operator.$accumulator == null) {
+    return;
+  }
+
+  for (const key of ['init', 'accumulate', 'merge', 'finalize']) {
+    if (typeof operator.$accumulator[key] === 'function') {
+      operator.$accumulator[key] = String(operator.$accumulator[key]);
+    }
+  }
+}

test/helpers/aggregate.test.js

@@ -0,0 +1,45 @@
+'use strict';
+
+const assert = require('assert');
+const stringifyAccumulatorOptions = require('../../lib/helpers/aggregate/stringifyAccumulatorOptions');
+
+describe('stringifyAccumulatorOptions', function() {
+  it('converts accumulator args to strings (gh-9364)', function() {
+    const pipeline = [{
+      $group: {
+        _id: '$author',
+        avgCopies: {
+          $accumulator: {
+            init: function() {
+              return { count: 0, sum: 0 };
+            },
+            accumulate: function(state, numCopies) {
+              return {
+                count: state.count + 1,
+                sum: state.sum + numCopies
+              };
+            },
+            accumulateArgs: ['$copies'],
+            merge: function(state1, state2) {
+              return {
+                count: state1.count + state2.count,
+                sum: state1.sum + state2.sum
+              };
+            },
+            finalize: function(state) {
+              return (state.sum / state.count);
+            },
+            lang: 'js'
+          }
+        }
+      }
+    }];
+
+    stringifyAccumulatorOptions(pipeline);
+
+    assert.equal(typeof pipeline[0].$group.avgCopies.$accumulator.init, 'string');
+    assert.equal(typeof pipeline[0].$group.avgCopies.$accumulator.accumulate, 'string');
+    assert.equal(typeof pipeline[0].$group.avgCopies.$accumulator.merge, 'string');
+    assert.equal(typeof pipeline[0].$group.avgCopies.$accumulator.finalize, 'string');
+  });
+});