Don't assume at least one closure function is encountered before tree-shaking. Allow…

runtime/vm/flow_graph_builder.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_builder.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/class_finalizer.h"
@@ skipping 2513 matching lines @@
   ReturnDefinition(instr);
 }
 
 
 // TODO(rmacnak): De-dup closures in inlined-finally and track down other
 // stragglers to use Class::closures instead.
 static void CollectClosureFunction(const Function& function) {
   if (function.HasCode()) return;
 
   Isolate* isolate = Isolate::Current();
-  if (isolate->collected_closures() == GrowableObjectArray::null()) {
-    isolate->set_collected_closures(
-        GrowableObjectArray::Handle(GrowableObjectArray::New()));
+  if (isolate->collected_closures() != GrowableObjectArray::null()) {

[srdjan, 2015/10/13 21:30:12]

Please add a comment why the check is necessary, even though it is invoked only
when precompiling.

[rmacnak, 2015/10/13 21:55:01]

Done.

+    const GrowableObjectArray& functions =
+        GrowableObjectArray::Handle(isolate, isolate->collected_closures());
+    functions.Add(function);
   }
-  const GrowableObjectArray& functions =
-      GrowableObjectArray::Handle(isolate, isolate->collected_closures());
-  functions.Add(function);
 }
 
 
 void EffectGraphVisitor::VisitClosureNode(ClosureNode* node) {
   const Function& function = node->function();
   if (FLAG_precompile_collect_closures) {
     CollectClosureFunction(function);
   }
 
   if (function.IsImplicitStaticClosureFunction()) {
@@ skipping 2143 matching lines @@
   Report::MessageF(Report::kBailout,
                    Script::Handle(function.script()),
                    function.token_pos(),
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart