Await it!

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index d80d951afc0fab08637eb1c456a4d57f554acaa2..8d4f60a722a88fc4072a2b0ef8246e8a2d4abc5c 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -5426,7 +5426,7 @@ void Parser::OpenFunctionBlock(const Function& func) {
 void Parser::OpenAsyncClosure() {
   TRACE_PARSER("OpenAsyncClosure");
   parsed_function()->set_await_temps_scope(current_block_->scope);
-  // TODO(mlippautz): Set up explicit jump table for await continuations.
+  current_block_->scope->LookupVariable(Symbols::Completer(), false);

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

Could you add a comment why the variable is looked up? I presume it's to mark it
captured as a side effect of the lookup.

[Michael Lippautz (Google), 2014/08/20 20:56:06]

Yes, it's about capturing it. Moved into CloseAsyncClosure() and added a
comment.

 }
 
 
@@ -5523,6 +5523,8 @@ SequenceNode* Parser::CloseAsyncFunction(const Function& closure,
   // Add to AST:
   //   var :async_op;
   //   var :async_completer;
+  //   var :await_jump_var;
+  //   var :await_ctx_var;
   LocalVariable* async_op_var = new (I) LocalVariable(
       Scanner::kNoSourcePos,
       Symbols::AsyncOperation(),
@@ -5537,11 +5539,34 @@ SequenceNode* Parser::CloseAsyncFunction(const Function& closure,
   current_block_->scope->AddVariable(async_completer);
   found = closure_body->scope()->CaptureVariable(Symbols::AsyncCompleter());
   ASSERT(found);
+  LocalVariable* await_jump_var = new (I) LocalVariable(
+      Scanner::kNoSourcePos,
+      Symbols::AwaitJumpVar(),
+      Type::ZoneHandle(I, Type::DynamicType()));
+  current_block_->scope->AddVariable(await_jump_var);
+  found = closure_body->scope()->CaptureVariable(Symbols::AwaitJumpVar());
+  ASSERT(found);
+  LocalVariable* await_ctx_var = new (I) LocalVariable(
+      Scanner::kNoSourcePos,
+      Symbols::AwaitContextVar(),
+      Type::ZoneHandle(I, Type::DynamicType()));
+  current_block_->scope->AddVariable(await_ctx_var);
+  found = closure_body->scope()->CaptureVariable(Symbols::AwaitContextVar());
+  ASSERT(found);
+
+  // Add to AST:
+  //   :await_jump_var = null;
+  //   :await_ctx_var = null;
+  AstNode* null_literal = new(I) LiteralNode(

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

You should not need to initialize these to null explicitly. The runtime will do
this automatically for all locals (and context variables).

[Michael Lippautz (Google), 2014/08/20 20:56:06]

Done.

+      Scanner::kNoSourcePos, Object::null_instance());
+  current_block_->statements->Add(new(I) StoreLocalNode(
+      Scanner::kNoSourcePos, await_jump_var, null_literal));
+  current_block_->statements->Add(new(I) StoreLocalNode(
+      Scanner::kNoSourcePos, await_ctx_var, null_literal));
 
   // Add to AST:
   //   :async_completer = new Completer();
-  ArgumentListNode* empty_args = new (I) ArgumentListNode(
-      Scanner::kNoSourcePos);
+  ArgumentListNode* empty_args = new(I) ArgumentListNode(Scanner::kNoSourcePos);

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

The prevalent type is new (I) (with space), please adapt code.

[Michael Lippautz (Google), 2014/08/20 20:56:06]

Done. I have seen "new(I)" and "new (I)" all around our codebase. Will write new
code with "new (I)".

   ConstructorCallNode* completer_constructor_node = new (I) ConstructorCallNode(
       Scanner::kNoSourcePos,
       TypeArguments::ZoneHandle(I),
@@ -5592,6 +5617,9 @@ void Parser::CloseAsyncClosure(SequenceNode* body) {
   TRACE_PARSER("CloseAsyncClosure");
   // We need a temporary expression to store intermediate return values.
   parsed_function()->EnsureExpressionTemp();
+  body->scope()->LookupVariable(Symbols::AwaitJumpVar(), false);

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

A comment would be nice explaining why you are looking up the variables.

[Michael Lippautz (Google), 2014/08/20 20:56:06]

Added a comment in the source.

Currently, all variables from all scopes are captured anyways. This lookup
ensures that if we do something smarter later on we will still have the
necessary internal variables available.

+  body->scope()->LookupVariable(Symbols::AwaitContextVar(), false);
+  body->scope()->RecursivelyCaptureAllVariables();
 }