fix(core): simplify serialization for code heap object (#122)

Summary:
MemLab could run out of memory if the JS heap under analysis has complex code heap objects (i.e., JS interpreted, and compiled code representation and their context graph in heap) which may take a lot of time and memory to serialize:
#122

This diff fixes this issue by simplifying the code heap object serialization process and output.

Reviewed By: tulga1970

Differential Revision: D59541476

fbshipit-source-id: a4eb00e0f914d4694a1fe562abe0c861ca641ad1

packages/core/src/lib/Config.ts

@@ -242,6 +242,7 @@ export class MemLabConfig {
   maxSamplesForClustering: number;
   filterTraceByName: Nullable<string>;
   skipBrowserCloseWait: boolean;
+  simplifyCodeSerialization: boolean;
 
   constructor(options: ConfigOption = {}) {
     // init properties, they can be configured manually
@@ -375,6 +376,9 @@ export class MemLabConfig {
     this.filterTraceByName = null;
     // if true, memlab will not wait for the browser to close successfully
     this.skipBrowserCloseWait = false;
+    // if true, serialized leak trace will have a simplified representation
+    // for code object, which could be large and cause OOM during serualization
+    this.simplifyCodeSerialization = !constant.isFB;
   }
 
   // initialize configurable parameters

packages/core/src/lib/Serializer.ts

@@ -329,18 +329,23 @@ function JSONifyCode(
   options: JSONifyOptions,
 ): ISerializedInfo {
   const info = Object.create(null);
+
   iterateSelectedEdges(node, (edge: IHeapEdge): Optional<{stop: boolean}> => {
     if (
       edge.name_or_index === 'name_or_scope_info' &&
       edge.toNode.name === '(function scope info)'
     ) {
       const key = 'variables with non-number values in closure scope chain';
-      info[key] = JSONifyNode(edge.toNode, args, options);
+      info[key] = config.simplifyCodeSerialization
+        ? JSONifyNodeOneLevel(edge.toNode)
+        : JSONifyNode(edge.toNode, args, options);
     } else if (edge.name_or_index === 'script_or_debug_info') {
       info['script URL'] = edge.toNode.name;
     } else {
       const key = filterJSONPropName(edge.name_or_index);
-      info[key] = JSONifyNode(edge.toNode, args, options);
+      info[key] = config.simplifyCodeSerialization
+        ? JSONifyNodeOneLevel(edge.toNode)
+        : JSONifyNode(edge.toNode, args, options);
     }
     return null;
   });