some progress

node_modules/mongoose/lib/helpers/aggregate/prepareDiscriminatorPipeline.js

@@ -0,0 +1,39 @@
+'use strict';
+
+module.exports = function prepareDiscriminatorPipeline(pipeline, schema, prefix) {
+  const discriminatorMapping = schema && schema.discriminatorMapping;
+  prefix = prefix || '';
+
+  if (discriminatorMapping && !discriminatorMapping.isRoot) {
+    const originalPipeline = pipeline;
+    const filterKey = (prefix.length > 0 ? prefix + '.' : prefix) + discriminatorMapping.key;
+    const discriminatorValue = discriminatorMapping.value;
+
+    // If the first pipeline stage is a match and it doesn't specify a `__t`
+    // key, add the discriminator key to it. This allows for potential
+    // aggregation query optimizations not to be disturbed by this feature.
+    if (originalPipeline[0] != null &&
+        originalPipeline[0].$match &&
+        (originalPipeline[0].$match[filterKey] === undefined || originalPipeline[0].$match[filterKey] === discriminatorValue)) {
+      originalPipeline[0].$match[filterKey] = discriminatorValue;
+      // `originalPipeline` is a ref, so there's no need for
+      // aggregate._pipeline = originalPipeline
+    } else if (originalPipeline[0] != null && originalPipeline[0].$geoNear) {
+      originalPipeline[0].$geoNear.query =
+          originalPipeline[0].$geoNear.query || {};
+      originalPipeline[0].$geoNear.query[filterKey] = discriminatorValue;
+    } else if (originalPipeline[0] != null && originalPipeline[0].$search) {
+      if (originalPipeline[1] && originalPipeline[1].$match != null) {
+        originalPipeline[1].$match[filterKey] = originalPipeline[1].$match[filterKey] || discriminatorValue;
+      } else {
+        const match = {};
+        match[filterKey] = discriminatorValue;
+        originalPipeline.splice(1, 0, { $match: match });
+      }
+    } else {
+      const match = {};
+      match[filterKey] = discriminatorValue;
+      originalPipeline.unshift({ $match: match });
+    }
+  }
+};

node_modules/mongoose/lib/helpers/aggregate/stringifyFunctionOperators.js

@@ -0,0 +1,50 @@
+'use strict';
+
+module.exports = function stringifyFunctionOperators(pipeline) {
+  if (!Array.isArray(pipeline)) {
+    return;
+  }
+
+  for (const stage of pipeline) {
+    if (stage == null) {
+      continue;
+    }
+
+    const canHaveAccumulator = stage.$group || stage.$bucket || stage.$bucketAuto;
+    if (canHaveAccumulator != null) {
+      for (const key of Object.keys(canHaveAccumulator)) {
+        handleAccumulator(canHaveAccumulator[key]);
+      }
+    }
+
+    const stageType = Object.keys(stage)[0];
+    if (stageType && typeof stage[stageType] === 'object') {
+      const stageOptions = stage[stageType];
+      for (const key of Object.keys(stageOptions)) {
+        if (stageOptions[key] != null &&
+            stageOptions[key].$function != null &&
+            typeof stageOptions[key].$function.body === 'function') {
+          stageOptions[key].$function.body = stageOptions[key].$function.body.toString();
+        }
+      }
+    }
+
+    if (stage.$facet != null) {
+      for (const key of Object.keys(stage.$facet)) {
+        stringifyFunctionOperators(stage.$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]);
+    }
+  }
+}