Fix deferred load errors / bug #26482

runtime/bin/loader.cc

Index: runtime/bin/loader.cc
diff --git a/runtime/bin/loader.cc b/runtime/bin/loader.cc
index f43cf30056225291aa737c67d9a5b46e6d4d8145..c4e472b1cd7a2147e5075452497fd6da3d6e89e6 100644
--- a/runtime/bin/loader.cc
+++ b/runtime/bin/loader.cc
@@ -213,17 +213,6 @@ void Loader::BlockUntilComplete() {
 
 
 bool Loader::ProcessResultLocked(Loader::IOResult* result) {
-  // A negative result tag indicates a loading error occurred in the service
-  // isolate. The payload is a C string of the error message.
-  if (result->tag < 0) {
-    error_ =
-        Dart_NewUnhandledExceptionError(
-            Dart_NewStringFromUTF8(result->payload,
-                                   result->payload_length));
-
-    return false;
-  }
-
   // We have to copy everything we care about out of |result| because after
   // dropping the lock below |result| may no longer valid.
   Dart_Handle uri =
@@ -233,6 +222,29 @@ bool Loader::ProcessResultLocked(Loader::IOResult* result) {
     library_uri =
         Dart_NewStringFromCString(reinterpret_cast<char*>(result->library_uri));
   }
+
+  // A negative result tag indicates a loading error occurred in the service
+  // isolate. The payload is a C string of the error message.
+  if (result->tag < 0) {
+    Dart_Handle library = Dart_LookupLibrary(uri);
+    Dart_Handle error = Dart_NewStringFromUTF8(result->payload,
+                                               result->payload_length);
+    // If a library with the given uri exists, give it a chance to handle
+    // the error. If the load requests stems from a deferred library load,
+    // an IO error is not fatal.
+    if ((library != Dart_Null()) && !Dart_IsError(library)) {

[hausner, 2016/06/07 21:47:05]

Is there a difference between x != Dart_Null() and !Dart_IsNull(x)?

I thought we typically use Dart_IsNull(), as you do a couple of lines below.

[Cutch, 2016/06/07 22:29:26]

No difference, but I switched to Dart_IsNull().

+      ASSERT(Dart_IsLibrary(library));
+      Dart_Handle res = Dart_LibraryHandleError(library, error);
+      if (Dart_IsNull(res)) {
+        return true;
+      }
+    }
+    // Fall through
+    error_ = Dart_NewUnhandledExceptionError(error);
+    return false;
+  }
+
+
   // Check for payload and load accordingly.
   bool is_snapshot = false;
   const uint8_t* payload = result->payload;