Fix bug where generators got closed prematurely.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index dd9744e7f6314d72f1b3b91ad4b28218da7d1225..5e88b58fefce96eecbd887e82005aee15decc139 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -4655,35 +4655,72 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
   {
     BlockState block_state(&scope_, inner_scope);
 
-    // For generators, allocate and yield an iterator on function entry.
     if (IsGeneratorFunction(kind)) {
-      ZoneList<Expression*>* arguments =
-          new(zone()) ZoneList<Expression*>(0, zone());
-      CallRuntime* allocation = factory()->NewCallRuntime(
-          Runtime::kCreateJSGeneratorObject, arguments, pos);
-      VariableProxy* init_proxy = factory()->NewVariableProxy(
-          function_state_->generator_object_variable());
-      Assignment* assignment = factory()->NewAssignment(
-          Token::INIT, init_proxy, allocation, RelocInfo::kNoPosition);
-      VariableProxy* get_proxy = factory()->NewVariableProxy(
-          function_state_->generator_object_variable());
-      Yield* yield = factory()->NewYield(
-          get_proxy, assignment, Yield::kInitial, RelocInfo::kNoPosition);
-      body->Add(factory()->NewExpressionStatement(
-          yield, RelocInfo::kNoPosition), zone());
-    }
+      // We produce:
+      //
+      // try { InitialYield; ...body...; FinalYield }
+      // finally { %GeneratorClose(generator) }
+      //
+      // - InitialYield yields the actual generator object.
+      // - FinalYield yields {value: foo, done: true} where foo is the
+      //   completion value of body.  (This is needed here in case the body
+      //   falls through without an explicit return.)
+      // - Any return statement inside the body will be converted into a similar
+      //   FinalYield.
+      // - If the generator terminates for whatever reason, we must close it.
+      //   Hence the finally clause.
+
+      Block* try_block =
+          factory()->NewBlock(nullptr, 3, false, RelocInfo::kNoPosition);
 
-    ParseStatementList(body, Token::RBRACE, CHECK_OK);
+      {
+        ZoneList<Expression*>* arguments =
+            new (zone()) ZoneList<Expression*>(0, zone());
+        CallRuntime* allocation = factory()->NewCallRuntime(
+            Runtime::kCreateJSGeneratorObject, arguments, pos);
+        VariableProxy* init_proxy = factory()->NewVariableProxy(
+            function_state_->generator_object_variable());
+        Assignment* assignment = factory()->NewAssignment(
+            Token::INIT, init_proxy, allocation, RelocInfo::kNoPosition);
+        VariableProxy* get_proxy = factory()->NewVariableProxy(
+            function_state_->generator_object_variable());
+        Yield* yield = factory()->NewYield(
+            get_proxy, assignment, Yield::kInitial, RelocInfo::kNoPosition);
+        try_block->statements()->Add(
+            factory()->NewExpressionStatement(yield, RelocInfo::kNoPosition),
+            zone());
+      }
+
+      ParseStatementList(try_block->statements(), Token::RBRACE, CHECK_OK);
 
-    if (IsGeneratorFunction(kind)) {
       VariableProxy* get_proxy = factory()->NewVariableProxy(
           function_state_->generator_object_variable());
       Expression* undefined =
           factory()->NewUndefinedLiteral(RelocInfo::kNoPosition);
       Yield* yield = factory()->NewYield(get_proxy, undefined, Yield::kFinal,
                                          RelocInfo::kNoPosition);
-      body->Add(factory()->NewExpressionStatement(
-          yield, RelocInfo::kNoPosition), zone());
+      try_block->statements()->Add(
+          factory()->NewExpressionStatement(yield, RelocInfo::kNoPosition),
+          zone());
+
+      Block* finally_block =
+          factory()->NewBlock(nullptr, 1, false, RelocInfo::kNoPosition);
+      ZoneList<Expression*>* args =
+          new (zone()) ZoneList<Expression*>(1, zone());
+      VariableProxy* call_proxy = factory()->NewVariableProxy(
+          function_state_->generator_object_variable());
+      args->Add(call_proxy, zone());
+      Expression* call = factory()->NewCallRuntime(
+          Runtime::kGeneratorClose, args, RelocInfo::kNoPosition);
+      finally_block->statements()->Add(
+          factory()->NewExpressionStatement(call, RelocInfo::kNoPosition),
+          zone());
+
+      body->Add(factory()->NewTryFinallyStatement(try_block, finally_block,
+                                                  RelocInfo::kNoPosition),
+                zone());
+    } else {
+      ParseStatementList(body, Token::RBRACE, CHECK_OK);
     }
 
     if (IsSubclassConstructor(kind)) {