Yield in non-generator function is compile-time error

runtime/vm/parser.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/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "platform/utils.h"
 #include "vm/ast_transformer.h"
 #include "vm/bootstrap.h"
@@ skipping 9581 matching lines @@
                 Token::Str(jump_kind));
   }
   return new(Z) JumpNode(jump_pos, jump_kind, target);
 }
 
 
 AstNode* Parser::ParseYieldStatement() {
   bool is_yield_each = false;
   const intptr_t yield_pos = TokenPos();
   ConsumeToken();  // yield reserved word.
-  ASSERT(innermost_function().IsGenerator() ||
-         innermost_function().IsSyncGenClosure() ||
-         innermost_function().IsAsyncGenerator() ||
-         innermost_function().IsAsyncGenClosure());
   if (CurrentToken() == Token::kMUL) {
     is_yield_each = true;
     ConsumeToken();
   }
+  if (!innermost_function().IsGenerator() &&
+      !innermost_function().IsGeneratorClosure()) {
+    ReportError(yield_pos,
+                "yield%s statement only allowed in generator functions",
+                is_yield_each ? "*" : "");
+  }
+
   AstNode* expr = ParseAwaitableExpr(kAllowConst, kConsumeCascades, NULL);
 
   LetNode* yield = new(Z) LetNode(yield_pos);
   if (innermost_function().IsSyncGenerator() ||
       innermost_function().IsSyncGenClosure()) {
     // Yield statement in sync* function.
 
     LocalVariable* iterator_param =
         LookupLocalScope(Symbols::IteratorParameter());
     ASSERT(iterator_param != NULL);
@@ skipping 3903 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart