Ensure that hash for a symbol is not set to 0 when it is made external.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 39255)
+++ runtime/vm/object.cc	(working copy)
@@ -17042,7 +17042,7 @@
     NoGCScope no_gc;
     ASSERT(array != NULL);
     intptr_t str_length = this->Length();
-    ASSERT(length >= (str_length * this->CharSize()));
+    RELEASE_ASSERT(length >= (str_length * this->CharSize()));
     intptr_t class_id = raw()->GetClassId();
     intptr_t used_size = 0;
     intptr_t original_size = 0;
@@ -17065,10 +17065,12 @@
       tags = RawObject::ClassIdTag::update(class_id, tags);
       raw_ptr()->tags_ = tags;
       result = this->raw();
+      const uint8_t* ext_array = reinterpret_cast<const uint8_t*>(array);
       ExternalStringData<uint8_t>* ext_data = new ExternalStringData<uint8_t>(
-          reinterpret_cast<const uint8_t*>(array), peer, cback);
-      result.SetLength(str_length);
-      result.SetHash(0);
+          ext_array, peer, cback);
+      RELEASE_ASSERT(result.Length() == str_length);
+      RELEASE_ASSERT(!result.HasHash() ||

[Ivan Posva, 2014/08/14 20:42:12]

We are aware that this makes the externalization of strings more expensive,
correct?

[siva, 2014/08/14 21:04:57]

Will change it to a plain ASSERT.

+                     (result.Hash() == String::Hash(ext_array, str_length)));

[koda, 2014/08/14 20:43:30]

This is costly to always run in release mode, and we still have no guarantee it
will continue to be true (underlying bytes can change at any time).

[siva, 2014/08/14 21:04:57]

See above changing to a plain ASSERT

       ExternalOneByteString::SetExternalData(result, ext_data);
       external_data = ext_data;
       finalizer = ExternalOneByteString::Finalize;
@@ -17091,10 +17093,12 @@
       tags = RawObject::ClassIdTag::update(class_id, tags);
       raw_ptr()->tags_ = tags;
       result = this->raw();
+      const uint16_t* ext_array = reinterpret_cast<const uint16_t*>(array);
       ExternalStringData<uint16_t>* ext_data = new ExternalStringData<uint16_t>(
-          reinterpret_cast<const uint16_t*>(array), peer, cback);
-      result.SetLength(str_length);
-      result.SetHash(0);
+          ext_array, peer, cback);
+      RELEASE_ASSERT(result.Length() == str_length);
+      RELEASE_ASSERT(!result.HasHash() ||
+                     (result.Hash() == String::Hash(ext_array, str_length)));
       ExternalTwoByteString::SetExternalData(result, ext_data);
       external_data = ext_data;
       finalizer = ExternalTwoByteString::Finalize;