Ensure PrintToJSONStream can be called on all heap objects without crashing.

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 4019 matching lines @@
   }
   return FinalizeHash(result);
 }
 
 
 RawString* TypeArguments::SubvectorName(intptr_t from_index,
                                         intptr_t len,
                                         NameVisibility name_visibility) const {
   ASSERT(from_index + len <= Length());
   String& name = String::Handle();
-  const intptr_t num_strings = 2*len + 1;  // "<""T"", ""T"">".
+  const intptr_t num_strings = (len == 0) ? 2 : 2*len + 1;  // "<""T"", ""T"">".
   const Array& strings = Array::Handle(Array::New(num_strings));
   intptr_t s = 0;
   strings.SetAt(s++, Symbols::LAngleBracket());
   AbstractType& type = AbstractType::Handle();
   for (intptr_t i = 0; i < len; i++) {
     type = TypeAt(from_index + i);
     name = type.BuildName(name_visibility);
     strings.SetAt(s++, name);
     if (i < len - 1) {
       strings.SetAt(s++, Symbols::CommaSpace());
@@ skipping 2267 matching lines @@
     selector = "closures";
   } else if (IsImplicitClosureFunction()) {
     id = cls.FindImplicitClosureFunctionIndex(*this);
     selector = "implicit_closures";
   } else if (IsNoSuchMethodDispatcher() || IsInvokeFieldDispatcher()) {
     id = cls.FindInvocationDispatcherFunctionIndex(*this);
     selector = "dispatchers";
   } else {
     id = cls.FindFunctionIndex(*this);
     selector = "functions";
   }

[turnidge, 2014/03/23 22:24:20]

Did you consider grabbing an id from the object id ring but not delegating up to
the Object::PrintToJSONStream.  Something like:

if (id >= 0) {
  jsobj.AddPropertyF("id", "classes/%" Pd " ... etc.
} else {
  jsobj.AddPropertyF("id", "objects/%" Pd "", <get a number from the obj id
ring>);
}

That way this will have the expected format of a Function and only the id will
be different.  Otherwise we will have to guard against these odd functions in
the observatory.

[koda, 2014/03/24 17:18:34]

I wasn't sure whether all fields still work in all the special cases (e.g., will
things like "parent_function" work?), but I suppose it makes sense to try.

I'll send a follow-up CL.

-  ASSERT(id >= 0);
+  // TODO(17697): Oddball functions are treated as plain objects and use the
+  // object id ring. Current known examples are signature functions of closures
+  // and stubs like 'megamorphic_miss'.
+  if (id < 0) {
+    return Object::PrintToJSONStream(stream, ref);
+  }
   intptr_t cid = cls.id();
   JSONObject jsobj(stream);
   jsobj.AddProperty("type", JSONType(ref));
   jsobj.AddPropertyF("id", "classes/%" Pd "/%s/%" Pd "", cid, selector, id);
   jsobj.AddProperty("name", internal_name);
   jsobj.AddProperty("user_name", user_name);
   jsobj.AddProperty("class", cls);
   const Function& parent = Function::Handle(parent_function());
   if (!parent.IsNull()) {
     jsobj.AddProperty("parent", parent);
@@ skipping 7134 matching lines @@
       OS::SNPrint(chars, len, format, class_name, args_cstr);
       return chars;
     }
   } else {
     return "Unresolved Type";
   }
 }
 
 
 void Type::PrintToJSONStream(JSONStream* stream, bool ref) const {
+  // TODO(koda): Decide whether to assign stable ids to non-canonical types.
+  if (!IsCanonical()) {
+    return Object::PrintToJSONStream(stream, ref);
+  }

[turnidge, 2014/03/23 22:24:20]

Ditto previous comment.  You could print an id from the object id ring but print
the rest of the expected properties for a Type.

[koda, 2014/03/24 17:18:34]

Also, here: not sure whether all printed properties are even defined for a
non-finalized type, for instance.

   ASSERT(IsCanonical());
   JSONObject jsobj(stream);
   jsobj.AddProperty("type", JSONType(ref));
   const Class& type_cls = Class::Handle(type_class());
   intptr_t id = type_cls.FindCanonicalTypeIndex(*this);
   ASSERT(id >= 0);
   intptr_t cid = type_cls.id();
   jsobj.AddPropertyF("id", "classes/%" Pd "/types/%" Pd "", cid, id);
   const char* name = String::Handle(Name()).ToCString();
   const char* user_name = String::Handle(UserVisibleName()).ToCString();
@@ skipping 3255 matching lines @@
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
   {
     JSONArray jsarr(&jsobj, "elements");
     for (intptr_t index = 0; index < Length(); index++) {
       JSONObject jselement(&jsarr);
       jselement.AddProperty("index", index);
 
-      Instance& instance = Instance::Handle();
-      instance ^= At(index);
-      jselement.AddProperty("value", instance);
+      Object& element = Object::Handle(At(index));
+      jselement.AddProperty("value", element);
     }
   }
 }
 
 
 RawArray* Array::Grow(const Array& source,
                       intptr_t new_length,
                       Heap::Space space) {
   const Array& result = Array::Handle(Array::New(new_length, space));
   intptr_t len = 0;
@@ skipping 317 matching lines @@
   jsobj.AddProperty("length", Length());
   if (ref) {
     return;
   }
   {
     JSONArray jsarr(&jsobj, "elements");
     for (intptr_t index = 0; index < Length(); index++) {
       JSONObject jselement(&jsarr);
       jselement.AddProperty("index", index);
 
-      Instance& instance = Instance::Handle();
-      instance ^= At(index);
-      jselement.AddProperty("value", instance);
+      Object& element = Object::Handle(At(index));
+      jselement.AddProperty("value", element);
     }
   }
 }
 
 
 RawFloat32x4* Float32x4::New(float v0, float v1, float v2, float v3,
                              Heap::Space space) {
   ASSERT(Isolate::Current()->object_store()->float32x4_class() !=
          Class::null());
   Float32x4& result = Float32x4::Handle();
@@ skipping 841 matching lines @@
   return "_MirrorReference";
 }
 
 
 void MirrorReference::PrintToJSONStream(JSONStream* stream, bool ref) const {
   Instance::PrintToJSONStream(stream, ref);
 }
 
 
 }  // namespace dart