Sane asynchronous debugging and stack traces

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index 923526885ecea9685b32b527aa03bcd12b6b9592..25d83e7bd725a320e01f56268f37f15562bb131b 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -3468,6 +3468,9 @@ SequenceNode* Parser::ParseFunc(const Function& func, bool check_semicolon) {
     ASSERT(!func.is_generated_body());
     // The code of an async function is synthesized. Disable debugging.
     func.set_is_debuggable(false);
+    // In order to produce sane asynchronous stacks we rely on this function
+    // not being inlined.
+    func.set_is_inlinable(false);
     generated_body_closure = OpenAsyncFunction(func.token_pos());
   } else if (func.IsAsyncClosure()) {
     // The closure containing the body of an async function is debuggable.
@@ -6808,6 +6811,9 @@ RawFunction* Parser::OpenAsyncFunction(TokenPosition async_func_pos) {
     closure = Function::NewClosureFunction(closure_name, innermost_function(),
                                            async_func_pos);
     closure.set_is_generated_body(true);
+    // In order to generate sane asynchronous stacks we rely on this function
+    // not being inlined.
+    closure.set_is_inlinable(false);
     closure.set_result_type(Object::dynamic_type());
     is_new_closure = true;
   }
@@ -6861,6 +6867,7 @@ void Parser::AddAsyncClosureVariables() {
   //   var :async_then_callback;
   //   var :async_catch_error_callback;
   //   var :async_completer;
+  //   var :async_stack_trace;
   LocalVariable* async_op_var =
       new (Z) LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                             Symbols::AsyncOperation(), Object::dynamic_type());
@@ -6877,6 +6884,10 @@ void Parser::AddAsyncClosureVariables() {
       new (Z) LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                             Symbols::AsyncCompleter(), Object::dynamic_type());
   current_block_->scope->AddVariable(async_completer);
+  LocalVariable* async_stack_trace = new (Z)
+      LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
+                    Symbols::AsyncStackTraceVar(), Object::dynamic_type());
+  current_block_->scope->AddVariable(async_stack_trace);
 }
 
 
@@ -6889,6 +6900,8 @@ void Parser::AddAsyncGeneratorVariables() {
   //   var :async_op;
   //   var :async_then_callback;
   //   var :async_catch_error_callback;
+  //   var :async_stack_trace;
+  //   var :controller_stream
   // These variables are used to store the async generator closure containing
   // the body of the async* function. They are used by the await operator.
   LocalVariable* controller_var =
@@ -6907,6 +6920,14 @@ void Parser::AddAsyncGeneratorVariables() {
       LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                     Symbols::AsyncCatchErrorCallback(), Object::dynamic_type());
   current_block_->scope->AddVariable(async_catch_error_callback_var);
+  LocalVariable* async_stack_trace = new (Z)
+      LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
+                    Symbols::AsyncStackTraceVar(), Object::dynamic_type());
+  current_block_->scope->AddVariable(async_stack_trace);
+  LocalVariable* controller_stream = new (Z)
+      LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
+                    Symbols::ControllerStream(), Object::dynamic_type());
+  current_block_->scope->AddVariable(controller_stream);
 }
 
 
@@ -6936,6 +6957,7 @@ RawFunction* Parser::OpenAsyncGeneratorFunction(TokenPosition async_func_pos) {
     closure = Function::NewClosureFunction(closure_name, innermost_function(),
                                            async_func_pos);
     closure.set_is_generated_body(true);
+    closure.set_is_inlinable(false);
     closure.set_result_type(Object::dynamic_type());
     is_new_closure = true;
   }
@@ -6976,7 +6998,8 @@ RawFunction* Parser::OpenAsyncGeneratorFunction(TokenPosition async_func_pos) {
 //   var :async_then_callback = _asyncThenWrapperHelper(:async_op);
 //   var :async_catch_error_callback = _asyncCatchErrorWrapperHelper(:async_op);
 //   :controller = new _AsyncStarStreamController(:async_op);
-//   return :controller.stream;
+//   var :controller_stream = :controller.stream;
+//   return :controller_stream;
 // }
 SequenceNode* Parser::CloseAsyncGeneratorFunction(const Function& closure_func,
                                                   SequenceNode* closure_body) {
@@ -7004,6 +7027,12 @@ SequenceNode* Parser::CloseAsyncGeneratorFunction(const Function& closure_func,
   existing_var = closure_body->scope()->LookupVariable(
       Symbols::AsyncCatchErrorCallback(), false);
   ASSERT((existing_var != NULL) && existing_var->is_captured());
+  existing_var = closure_body->scope()->LookupVariable(
+      Symbols::AsyncStackTraceVar(), false);
+  ASSERT((existing_var != NULL) && existing_var->is_captured());
+  existing_var =
+      closure_body->scope()->LookupVariable(Symbols::ControllerStream(), false);
+  ASSERT((existing_var != NULL) && existing_var->is_captured());
 
   const Library& async_lib = Library::Handle(Library::AsyncLibrary());
 
@@ -7015,6 +7044,8 @@ SequenceNode* Parser::CloseAsyncGeneratorFunction(const Function& closure_func,
       Z, controller_class.LookupConstructorAllowPrivate(
              Symbols::_AsyncStarStreamControllerConstructor()));
 
+  TokenPosition token_pos = TokenPosition::kNoSource;
+
   // :await_jump_var = -1;
   LocalVariable* jump_var =
       current_block_->scope->LookupVariable(Symbols::AwaitJumpVar(), false);
@@ -7034,6 +7065,24 @@ SequenceNode* Parser::CloseAsyncGeneratorFunction(const Function& closure_func,
 
   current_block_->statements->Add(store_async_op);
 
+  // Add to AST:
+  //   :async_stack_trace = _asyncStackTraceHelper(:async_op);
+  const Function& async_stack_trace_helper = Function::ZoneHandle(
+      Z,
+      async_lib.LookupFunctionAllowPrivate(Symbols::AsyncStackTraceHelper()));
+  ASSERT(!async_stack_trace_helper.IsNull());
+  ArgumentListNode* async_stack_trace_helper_args =
+      new (Z) ArgumentListNode(TokenPosition::kNoSource);
+  async_stack_trace_helper_args->Add(
+      new (Z) LoadLocalNode(TokenPosition::kNoSource, async_op_var));
+  StaticCallNode* async_stack_trace_helper_call = new (Z) StaticCallNode(
+      token_pos, async_stack_trace_helper, async_stack_trace_helper_args);
+  LocalVariable* async_stack_trace_var = current_block_->scope->LookupVariable(
+      Symbols::AsyncStackTraceVar(), false);
+  StoreLocalNode* store_async_stack_trace = new (Z) StoreLocalNode(
+      token_pos, async_stack_trace_var, async_stack_trace_helper_call);
+  current_block_->statements->Add(store_async_stack_trace);
+
   // :async_then_callback = _asyncThenWrapperHelper(:async_op)
   const Function& async_then_wrapper_helper = Function::ZoneHandle(
       Z,
@@ -7090,13 +7139,28 @@ SequenceNode* Parser::CloseAsyncGeneratorFunction(const Function& closure_func,
       TokenPosition::kNoSource, controller_var, controller_constructor_call);
   current_block_->statements->Add(store_controller);
 
-  // return :controller.stream;
+  // Grab :controller.stream
+  InstanceGetterNode* controller_stream = new (Z) InstanceGetterNode(
+      TokenPosition::kNoSource,
+      new (Z) LoadLocalNode(TokenPosition::kNoSource, controller_var),
+      Symbols::Stream());
+
+  // Store :controller.stream into :controller_stream inside the closure.
+  // We have to remember the stream because a new instance is generated for
+  // each getter invocation and in order to recreate the linkage, we need the
+  // awaited on instance.
+  LocalVariable* controller_stream_var =
+      current_block_->scope->LookupVariable(Symbols::ControllerStream(), false);
+  ASSERT(controller_stream_var != NULL);
+
+  StoreLocalNode* store_controller_stream = new (Z) StoreLocalNode(
+      TokenPosition::kNoSource, controller_stream_var, controller_stream);
+  current_block_->statements->Add(store_controller_stream);
+
+  // return :controller_stream;
   ReturnNode* return_node = new (Z) ReturnNode(
       TokenPosition::kNoSource,
-      new (Z) InstanceGetterNode(
-          TokenPosition::kNoSource,
-          new (Z) LoadLocalNode(TokenPosition::kNoSource, controller_var),
-          Symbols::Stream()));
+      new (Z) LoadLocalNode(TokenPosition::kNoSource, controller_stream_var));
   current_block_->statements->Add(return_node);
   return CloseBlock();
 }
@@ -7166,6 +7230,9 @@ SequenceNode* Parser::CloseAsyncFunction(const Function& closure,
   existing_var =
       closure_body->scope()->LookupVariable(Symbols::AsyncCompleter(), false);
   ASSERT((existing_var != NULL) && existing_var->is_captured());
+  existing_var = closure_body->scope()->LookupVariable(
+      Symbols::AsyncStackTraceVar(), false);
+  ASSERT((existing_var != NULL) && existing_var->is_captured());
 
   // Create and return a new future that executes a closure with the current
   // body.
@@ -7185,6 +7252,8 @@ SequenceNode* Parser::CloseAsyncFunction(const Function& closure,
       Z, completer.LookupFunction(Symbols::CompleterSyncConstructor()));
   ASSERT(!completer_constructor.IsNull());
 
+  const Library& async_lib = Library::Handle(Library::AsyncLibrary());
+
   LocalVariable* async_completer =
       current_block_->scope->LookupVariable(Symbols::AsyncCompleter(), false);
 
@@ -7217,7 +7286,24 @@ SequenceNode* Parser::CloseAsyncFunction(const Function& closure,
       new (Z) StoreLocalNode(token_pos, async_op_var, cn);
   current_block_->statements->Add(store_async_op);
 
-  const Library& async_lib = Library::Handle(Library::AsyncLibrary());
+  // Add to AST:
+  //   :async_stack_trace = _asyncStackTraceHelper(:async_op);
+  const Function& async_stack_trace_helper = Function::ZoneHandle(
+      Z,
+      async_lib.LookupFunctionAllowPrivate(Symbols::AsyncStackTraceHelper()));
+  ASSERT(!async_stack_trace_helper.IsNull());
+  ArgumentListNode* async_stack_trace_helper_args =
+      new (Z) ArgumentListNode(token_pos);
+  async_stack_trace_helper_args->Add(
+      new (Z) LoadLocalNode(token_pos, async_op_var));
+  StaticCallNode* async_stack_trace_helper_call = new (Z) StaticCallNode(
+      token_pos, async_stack_trace_helper, async_stack_trace_helper_args);
+  LocalVariable* async_stack_trace_var = current_block_->scope->LookupVariable(
+      Symbols::AsyncStackTraceVar(), false);
+  StoreLocalNode* store_async_stack_trace = new (Z) StoreLocalNode(
+      token_pos, async_stack_trace_var, async_stack_trace_helper_call);
+  current_block_->statements->Add(store_async_stack_trace);
+
   // :async_then_callback = _asyncThenWrapperHelper(:async_op)
   const Function& async_then_wrapper_helper = Function::ZoneHandle(
       Z,
@@ -8779,6 +8865,36 @@ AstNode* Parser::ParseAwaitForStatement(String* label_name) {
       ParseAwaitableExpr(kAllowConst, kConsumeCascades, NULL);
   ExpectToken(Token::kRPAREN);
 
+  // Create :stream to store the stream into temporarily.
+  LocalVariable* stream_var =
+      new (Z) LocalVariable(stream_expr_pos, stream_expr_pos,
+                            Symbols::ColonStream(), Object::dynamic_type());
+  current_block_->scope->AddVariable(stream_var);
+
+  // Store the stream expression into a variable.
+  StoreLocalNode* store_stream_var =
+      new (Z) StoreLocalNode(stream_expr_pos, stream_var, stream_expr);
+  current_block_->statements->Add(store_stream_var);
+
+  // Register the awaiter on the stream by invoking `_asyncStarListenHelper`.
+  const Library& async_lib = Library::Handle(Library::AsyncLibrary());
+  const Function& async_star_listen_helper = Function::ZoneHandle(
+      Z,
+      async_lib.LookupFunctionAllowPrivate(Symbols::_AsyncStarListenHelper()));
+  ASSERT(!async_star_listen_helper.IsNull());
+  LocalVariable* async_op_var =
+      current_block_->scope->LookupVariable(Symbols::AsyncOperation(), false);
+  ASSERT(async_op_var != NULL);
+  ArgumentListNode* async_star_listen_helper_args =
+      new (Z) ArgumentListNode(stream_expr_pos);
+  async_star_listen_helper_args->Add(
+      new (Z) LoadLocalNode(stream_expr_pos, stream_var));
+  async_star_listen_helper_args->Add(
+      new (Z) LoadLocalNode(stream_expr_pos, async_op_var));
+  StaticCallNode* async_star_listen_helper_call = new (Z) StaticCallNode(
+      stream_expr_pos, async_star_listen_helper, async_star_listen_helper_args);
+  current_block_->statements->Add(async_star_listen_helper_call);
+
   // Build creation of implicit StreamIterator.
   // var :for-in-iter = new StreamIterator(stream_expr).
   const Class& stream_iterator_cls =
@@ -8789,7 +8905,7 @@ AstNode* Parser::ParseAwaitForStatement(String* label_name) {
       stream_iterator_cls.LookupFunction(Symbols::StreamIteratorConstructor()));
   ASSERT(!iterator_ctor.IsNull());
   ArgumentListNode* ctor_args = new (Z) ArgumentListNode(stream_expr_pos);
-  ctor_args->Add(stream_expr);
+  ctor_args->Add(new (Z) LoadLocalNode(stream_expr_pos, stream_var));
   ConstructorCallNode* ctor_call = new (Z) ConstructorCallNode(
       stream_expr_pos, TypeArguments::ZoneHandle(Z), iterator_ctor, ctor_args);
   const AbstractType& iterator_type = Object::dynamic_type();
@@ -8834,7 +8950,23 @@ AstNode* Parser::ParseAwaitForStatement(String* label_name) {
   AstNode* iterator_moveNext = new (Z) InstanceCallNode(
       stream_expr_pos, new (Z) LoadLocalNode(stream_expr_pos, iterator_var),
       Symbols::MoveNext(), no_args);
+
   OpenBlock();
+  // Give the debugger an opportunity to 'step into' the generator by
+  // calling '_asyncStarMoveNextHelper'.
+  const Function& async_star_move_next_helper =
+      Function::ZoneHandle(Z, async_lib.LookupFunctionAllowPrivate(
+                                  Symbols::_AsyncStarMoveNextHelper()));
+  ASSERT(!async_star_move_next_helper.IsNull());
+  ASSERT(async_op_var != NULL);
+  ArgumentListNode* async_star_move_next_helper_args =
+      new (Z) ArgumentListNode(stream_expr_pos);
+  async_star_move_next_helper_args->Add(
+      new (Z) LoadLocalNode(stream_expr_pos, stream_var));
+  StaticCallNode* async_star_move_next_helper_call =
+      new (Z) StaticCallNode(stream_expr_pos, async_star_move_next_helper,
+                             async_star_move_next_helper_args);
+  current_block_->statements->Add(async_star_move_next_helper_call);
   AstNode* await_moveNext = new (Z) AwaitNode(
       stream_expr_pos, iterator_moveNext, saved_try_ctx, async_saved_try_ctx,
       outer_saved_try_ctx, outer_async_saved_try_ctx, current_block_->scope);