Eliminate a potential crash in the struct layout code with a gracefull fallback

[tberghammer]

Summary

Eliminate a potential crash in the struct layout code with a gracefull fallback

lldb/trunk/source/Expression/ClangASTSource.cpp

if (origin_record.IsInvalid())
         return false;
 
     FieldOffsetMap origin_field_offsets;
     BaseOffsetMap origin_base_offsets;
     BaseOffsetMap origin_virtual_base_offsets;
 
     ClangASTContext::GetCompleteDecl(&origin_record->getASTContext(), const_cast<RecordDecl*>(origin_record.decl));
 
-    if (!origin_record.decl->getDefinition())
+    clang::RecordDecl* definition = origin_record.decl->getDefinition();
+    if (!definition || !definition->isCompleteDefinition())
         return false;
 
     const ASTRecordLayout &record_layout(origin_record->getASTContext().getASTRecordLayout(origin_record.decl));
 
     int field_idx = 0, field_count = record_layout.getFieldCount();
 
     for (RecordDecl::field_iterator fi = origin_record->field_begin(), fe = origin_record->field_end(); fi != fe; ++fi)
     {