Track the 'awaiter return' call stack use it to detect uncaught exceptions in async functions

runtime/vm/compiler.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/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 525 matching lines @@
   const Array& deopt_info_array =
       Array::Handle(zone, graph_compiler->CreateDeoptInfo(assembler));
   INC_STAT(thread(), total_code_size,
            deopt_info_array.Length() * sizeof(uword));
   // Allocates instruction object. Since this occurs only at safepoint,
   // there can be no concurrent access to the instruction page.
   const Code& code =
       Code::Handle(Code::FinalizeCode(function, assembler, optimized()));
   code.set_is_optimized(optimized());
   code.set_owner(function);
+#if !defined(PRODUCT)
+  if (FLAG_support_debugger) {
+    ZoneGrowableArray<TokenPosition>* await_token_positions =
+        flow_graph->await_token_positions();
+    if (await_token_positions != NULL) {
+      Smi& token_pos_value = Smi::Handle(zone);
+      if (await_token_positions->length() > 0) {
+        const Array& await_to_token_map = Array::Handle(
+            zone, Array::New(await_token_positions->length(), Heap::kOld));
+        ASSERT(!await_to_token_map.IsNull());
+        for (intptr_t i = 0; i < await_token_positions->length(); i++) {
+          TokenPosition token_pos =
+              await_token_positions->At(i).FromSynthetic();
+          if (!token_pos.IsReal()) {
+            // Some async machinary uses sentinel values. Map them to
+            // no source position.
+            token_pos_value = Smi::New(TokenPosition::kNoSourcePos);
+          } else {
+            token_pos_value = Smi::New(token_pos.value());
+          }
+          await_to_token_map.SetAt(i, token_pos_value);
+        }
+        code.SetAwaitTokenPositions(await_to_token_map);
+      }
+    }
+  }
+#endif  // !defined(PRODUCT)
+
   if (!function.IsOptimizable()) {
     // A function with huge unoptimized code can become non-optimizable
     // after generating unoptimized code.
     function.set_usage_counter(INT_MIN);
   }
 
   graph_compiler->FinalizePcDescriptors(code);
   code.set_deopt_info_array(deopt_info_array);
 
   graph_compiler->FinalizeStackMaps(code);
@@ skipping 1711 matching lines @@
 
 
 bool BackgroundCompiler::IsDisabled() {
   UNREACHABLE();
   return true;
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart