Await it!

runtime/vm/scopes.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/scopes.h"
 
 #include "vm/object.h"
 #include "vm/stack_frame.h"
 #include "vm/symbols.h"
 
@@ skipping 584 matching lines @@
     LocalScope* owner_scope = new LocalScope(NULL, 0, 0);
     owner_scope->set_context_level(context_scope.ContextLevelAt(i));
     owner_scope->AddVariable(variable);
     outer_scope->AddVariable(variable);  // As alias.
     ASSERT(variable->owner() == owner_scope);
   }
   return outer_scope;
 }
 
 
+void LocalScope::RecursivelyCaptureAllVariables() {
+  bool found = false;
+  for (intptr_t i = 0; i < num_variables(); i++) {
+    if (VariableAt(i)->name().raw() == Symbols::StackTraceVar().raw() ||
+        VariableAt(i)->name().raw() == Symbols::ExceptionVar().raw()) {

[srdjan, 2014/08/20 17:50:06]

Please add parentheses.

[Michael Lippautz (Google), 2014/08/20 20:56:07]

Done.

+      // Don't capture those variables as there scope of use can not be

[hausner, 2014/08/20 19:47:48]

there -> their

I'm not sure what the "scope of use" of a variable is.

[Michael Lippautz (Google), 2014/08/20 20:56:07]

There is no way to interrupt those variable's scopes with an await expression.
In other words: They will be assigned variables and it is not possible to reach
an await until they are read.

I didn't want to break the FlowGraphBuilder's assumption on them lying on the
stack. (flow_graph_builder.h:3896-3897)

+      // interrupted by await.

[srdjan, 2014/08/20 17:50:06]

s/there/their/ ?

[Michael Lippautz (Google), 2014/08/20 20:56:07]

Done.

+      continue;
+    }
+    found = CaptureVariable(VariableAt(i)->name());
+    VariableAt(i)->set_is_captured();

[hausner, 2014/08/20 19:47:48]

Why do you need to set the variable as captured again?

[Michael Lippautz (Google), 2014/08/20 20:56:07]

CaptureVariable() conveniently manages regular capturing of variables but does
not mark variables on the same context level as captured. However, for await we
also need to capture those.

Example:
  for (int i = 0; ...; ...) {...}

"i" needs to be captured, but CaptureVariable() sees that it's on the same scope
level (somewhere in the for loop) and won't do anything here.

[hausner, 2014/08/20 21:42:52]

Maybe a one-liner comment might help a future reader who has the same question.

On 2014/08/20 20:56:07, Michael Lippautz wrote:

[Michael Lippautz (Google), 2014/08/21 16:39:14]

Done.

+    ASSERT(found);
+  }
+  if (sibling() != NULL) { sibling()->RecursivelyCaptureAllVariables(); }
+  if (child() != NULL) { child()->RecursivelyCaptureAllVariables(); }
+}
+
+
+
 RawContextScope* LocalScope::CreateImplicitClosureScope(const Function& func) {
   static const intptr_t kNumCapturedVars = 1;
 
   // Create a ContextScope with space for kNumCapturedVars descriptors.
   const ContextScope& context_scope =
       ContextScope::Handle(ContextScope::New(kNumCapturedVars));
 
   // Create a descriptor for 'this' variable.
   context_scope.SetTokenIndexAt(0, func.token_pos());
   context_scope.SetNameAt(0, Symbols::This());
@@ skipping 33 matching lines @@
     return fixed_parameter_count - (index() - kParamEndSlotFromFp);
   } else {
     // Shift negative indexes so that the lowest one is 0 (they are still
     // non-positive).
     return fixed_parameter_count - (index() - kFirstLocalSlotFromFp);
   }
 }
 
 
 }  // namespace dart