[debugger] Prevent shared function info duplicates

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 8eb6ff577308015c0ec7ee0e7984d04d4e43ac81..dc02d51e43820c6a73046c9f82817b6591e9e0a3 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -1242,6 +1242,12 @@ bool Compiler::CompileForLiveEdit(Handle<Script> script) {
   Isolate* isolate = script->GetIsolate();
   DCHECK(AllowCompilation::IsAllowed(isolate));
 
+  // In order to ensure that live edit function info collection finds the newly
+  // generated shared function infos, clear the script's list temporarily
+  // and restore it at the end of this method.
+  Handle<Object> old_function_infos(script->shared_function_infos(), isolate);
+  script->set_shared_function_infos(Smi::FromInt(0));
+
   // Start a compilation.
   Zone zone(isolate->allocator());
   ParseInfo parse_info(&zone, script);
@@ -1249,13 +1255,19 @@ bool Compiler::CompileForLiveEdit(Handle<Script> script) {
   parse_info.set_global();
   info.MarkAsDebug();
   // TODO(635): support extensions.
-  if (CompileToplevel(&info).is_null()) {
-    return false;
+  const bool compilation_succeeded = CompileToplevel(&info).is_null();
+
+  // Restore the original function info list in order to remain 'side-effect
+  // free' as much as possible, since some code expects the old shared function
+  // infos to stick around.
+  script->set_shared_function_infos(*old_function_infos);
+
+  if (compilation_succeeded) {
+    // Check postconditions on success.
+    DCHECK(!isolate->has_pending_exception());

[Yang, 2016/05/12 07:43:14]

We could just rephrase this as DCHECK(!compilation_succeeded ||
!isolate->has_pending_exception());

[jgruber1, 2016/05/12 08:26:46]

Rewrote this part to again exit early on compilation failure since we have some
more logic coming up in the successful case.

   }
 
-  // Check postconditions on success.
-  DCHECK(!isolate->has_pending_exception());
-  return true;
+  return compilation_succeeded;
 }
 
 // TODO(turbofan): In the future, unoptimized code with deopt support could