Wrap lazy compilation errors when parsing metadata. Addresses the poor error reporting in issue 120…

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
===================================================================
--- runtime/lib/mirrors.cc	(revision 25492)
+++ runtime/lib/mirrors.cc	(working copy)
@@ -981,6 +981,28 @@
 }
 
 
+static void ThrowMirroredCompilationError(const String& message) {
+  Array& args = Array::Handle(Array::New(1));
+  args.SetAt(0, message);
+
+  Exceptions::ThrowByType(Exceptions::kMirroredCompilationError, args);
+  UNREACHABLE();
+}
+
+
+static void ThrowInvokeError(const Error& error) {
+  if (error.IsLanguageError()) {
+    // A compilation error that was delayed by lazy compilation.
+    const LanguageError& compilation_error = LanguageError::Cast(error);
+    String& message = String::Handle(compilation_error.message());
+    ThrowMirroredCompilationError(message);
+    UNREACHABLE();
+  }
+  Exceptions::PropagateError(error);
+  UNREACHABLE();
+}
+
+
 DEFINE_NATIVE_ENTRY(DeclarationMirror_metadata, 1) {
   const MirrorReference& decl_ref =
       MirrorReference::CheckedHandle(arguments->NativeArgAt(0));
@@ -998,7 +1020,11 @@
   }
 
   const Library& library = Library::Handle(klass.library());
-  return library.GetMetadata(decl);
+  const Object& metadata = Object::Handle(library.GetMetadata(decl));
+  if (metadata.IsError()) {
+    ThrowInvokeError(Error::Cast(metadata));
+  }
+  return metadata.raw();
 }
 
 
@@ -1009,28 +1035,6 @@
 }
 
 
-static void ThrowMirroredCompilationError(const String& message) {
-  Array& args = Array::Handle(Array::New(1));
-  args.SetAt(0, message);
-
-  Exceptions::ThrowByType(Exceptions::kMirroredCompilationError, args);
-  UNREACHABLE();
-}
-
-
-static void ThrowInvokeError(const Error& error) {
-  if (error.IsLanguageError()) {
-    // A compilation error that was delayed by lazy compilation.
-    const LanguageError& compilation_error = LanguageError::Cast(error);
-    String& message = String::Handle(compilation_error.message());
-    ThrowMirroredCompilationError(message);
-    UNREACHABLE();
-  }
-  Exceptions::PropagateError(error);
-  UNREACHABLE();
-}
-
-
 static bool FieldIsUninitialized(const Field& field) {
   ASSERT(!field.IsNull());