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authorjanekptacijarabaci <janekptacijarabaci@seznam.cz>2018-03-25 14:20:11 +0200
committerjanekptacijarabaci <janekptacijarabaci@seznam.cz>2018-03-25 14:20:11 +0200
commit4ee42e38e0a490eb4880b4a260e3cbe07dd486d1 (patch)
treef923d15f26214678fe0bac821e9658503ce98157
parentc93787917dbf305aa622d2d288effff78fe81008 (diff)
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Bug 1338796 - Do not call iterator.return if iterator.throw is present in yield*
Issue #74
-rw-r--r--js/src/frontend/BytecodeEmitter.cpp280
-rw-r--r--js/src/frontend/BytecodeEmitter.h4
-rw-r--r--js/src/tests/ecma_6/Generators/yield-star-iterator-close.js38
-rw-r--r--js/src/tests/ecma_6/shell.js7
4 files changed, 197 insertions, 132 deletions
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index b1b0055e2..4a60f1cf1 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -5141,7 +5141,7 @@ BytecodeEmitter::emitIteratorNext(ParseNode* pn, bool allowSelfHosted)
}
bool
-BytecodeEmitter::emitIteratorClose(Maybe<JumpTarget> yieldStarTryStart, bool allowSelfHosted)
+BytecodeEmitter::emitIteratorClose(bool allowSelfHosted)
{
MOZ_ASSERT(allowSelfHosted || emitterMode != BytecodeEmitter::SelfHosting,
".close() on iterators is prohibited in self-hosted code because it "
@@ -5180,86 +5180,11 @@ BytecodeEmitter::emitIteratorClose(Maybe<JumpTarget> yieldStarTryStart, bool all
// an Object.
if (!emit1(JSOP_SWAP)) // ... RET ITER
return false;
-
- // ES 14.4.13, yield * AssignmentExpression, step 5.c
- //
- // When emitting iterator.return() for yield* forced return, we need to
- // pass the argument passed to Generator.prototype.return to the return
- // method.
- if (yieldStarTryStart) {
- IfThenElseEmitter ifGeneratorClosing(this);
- if (!emitDupAt(2)) // ... FTYPE FVALUE RET ITER FVALUE
- return false;
- if (!emit1(JSOP_ISGENCLOSING)) // ... FTYPE FVALUE RET ITER FVALUE CLOSING
- return false;
- if (!emit1(JSOP_SWAP)) // ... FTYPE FVALUE RET ITER CLOSING FVALUE
- return false;
- if (!emit1(JSOP_POP)) // ... FTYPE FVALUE RET ITER CLOSING
- return false;
- if (!ifGeneratorClosing.emitIfElse()) // ... FTYPE FVALUE RET ITER
- return false;
-
- if (!emit1(JSOP_GETRVAL)) // ... FTYPE FVALUE RET ITER RVAL
- return false;
- if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ... FTYPE FVALUE RET ITER VALUE
- return false;
- if (!emitCall(JSOP_CALL, 1)) // ... FTYPE FVALUE RESULT
- return false;
- checkTypeSet(JSOP_CALL);
- if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ... FTYPE FVALUE RESULT
- return false;
-
- IfThenElseEmitter ifReturnDone(this);
- if (!emit1(JSOP_DUP)) // ITER OLDRESULT FTYPE FVALUE RESULT RESULT
- return false;
- if (!emitAtomOp(cx->names().done, JSOP_GETPROP)) // ITER OLDRESULT FTYPE FVALUE RESULT DONE
- return false;
- if (!ifReturnDone.emitIfElse()) // ITER OLDRESULT FTYPE FVALUE RESULT
- return false;
- if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ITER OLDRESULT FTYPE FVALUE VALUE
- return false;
- if (!emitPrepareIteratorResult()) // ITER OLDRESULT FTYPE FVALUE VALUE RESULT
- return false;
- if (!emit1(JSOP_SWAP)) // ITER OLDRESULT FTYPE FVALUE RESULT VALUE
- return false;
- if (!emitFinishIteratorResult(true)) // ITER OLDRESULT FTYPE FVALUE RESULT
- return false;
- if (!emit1(JSOP_DUP)) // ITER OLDRESULT FTYPE FVALUE RESULT RESULT
- return false;
- if (!emit1(JSOP_SETRVAL)) // ITER OLDRESULT FTYPE FVALUE RESULT
- return false;
- if (!ifReturnDone.emitElse()) // ITER OLDRESULT FTYPE FVALUE RESULT
- return false;
- int32_t savedDepth = this->stackDepth;
- if (!emit2(JSOP_UNPICK, 3)) // ITER RESULT OLDRESULT FTYPE FVALUE
- return false;
- if (!emitUint16Operand(JSOP_POPN, 3)) // ITER RESULT
- return false;
- JumpList beq;
- JumpTarget breakTarget{ -1 };
- if (!emitBackwardJump(JSOP_GOTO, *yieldStarTryStart, &beq, &breakTarget)) // ITER RESULT
- return false;
- this->stackDepth = savedDepth;
- if (!ifReturnDone.emitEnd())
- return false;
-
- if (!ifGeneratorClosing.emitElse()) // ... FTYPE FVALUE RET ITER
- return false;
- if (!emitCall(JSOP_CALL, 0)) // ... FTYPE FVALUE RESULT
- return false;
- checkTypeSet(JSOP_CALL);
- if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ... FTYPE FVALUE RESULT
- return false;
-
- if (!ifGeneratorClosing.emitEnd())
- return false;
- } else {
- if (!emitCall(JSOP_CALL, 0)) // ... RESULT
- return false;
- checkTypeSet(JSOP_CALL);
- if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ... RESULT
- return false;
- }
+ if (!emitCall(JSOP_CALL, 0)) // ... RESULT
+ return false;
+ checkTypeSet(JSOP_CALL);
+ if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ... RESULT
+ return false;
if (!ifReturnMethodIsDefined.emitElse())
return false;
@@ -8227,93 +8152,202 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter, ParseNode* gen)
MOZ_ASSERT(sc->isFunctionBox());
MOZ_ASSERT(sc->asFunctionBox()->isStarGenerator());
- if (!emitTree(iter)) // ITERABLE
+ if (!emitTree(iter)) // ITERABLE
return false;
- if (!emitIterator()) // ITER
+ if (!emitIterator()) // ITER
return false;
// Initial send value is undefined.
- if (!emit1(JSOP_UNDEFINED)) // ITER RECEIVED
+ if (!emit1(JSOP_UNDEFINED)) // ITER RECEIVED
return false;
- int depth = stackDepth;
- MOZ_ASSERT(depth >= 2);
+ int32_t savedDepthTemp;
+ int32_t startDepth = stackDepth;
+ MOZ_ASSERT(startDepth >= 2);
TryEmitter tryCatch(this, TryEmitter::TryCatchFinally, TryEmitter::DontUseRetVal,
TryEmitter::DontUseControl);
- if (!tryCatch.emitJumpOverCatchAndFinally()) // ITER RESULT
+ if (!tryCatch.emitJumpOverCatchAndFinally()) // ITER RESULT
return false;
JumpTarget tryStart{ offset() };
- if (!tryCatch.emitTry()) // ITER RESULT
+ if (!tryCatch.emitTry()) // ITER RESULT
return false;
- MOZ_ASSERT(this->stackDepth == depth);
+ MOZ_ASSERT(this->stackDepth == startDepth);
// Load the generator object.
- if (!emitTree(gen)) // ITER RESULT GENOBJ
+ if (!emitTree(gen)) // ITER RESULT GENOBJ
return false;
// Yield RESULT as-is, without re-boxing.
- if (!emitYieldOp(JSOP_YIELD)) // ITER RECEIVED
+ if (!emitYieldOp(JSOP_YIELD)) // ITER RECEIVED
return false;
- if (!tryCatch.emitCatch()) // ITER RESULT
+ if (!tryCatch.emitCatch()) // ITER RESULT
return false;
- stackDepth = uint32_t(depth); // ITER RESULT
- if (!emit1(JSOP_EXCEPTION)) // ITER RESULT EXCEPTION
+ stackDepth = startDepth; // ITER RESULT
+ if (!emit1(JSOP_EXCEPTION)) // ITER RESULT EXCEPTION
return false;
- if (!emitDupAt(2)) // ITER RESULT EXCEPTION ITER
+ if (!emitDupAt(2)) // ITER RESULT EXCEPTION ITER
return false;
- if (!emit1(JSOP_DUP)) // ITER RESULT EXCEPTION ITER ITER
+ if (!emit1(JSOP_DUP)) // ITER RESULT EXCEPTION ITER ITER
return false;
- if (!emitAtomOp(cx->names().throw_, JSOP_CALLPROP)) // ITER RESULT EXCEPTION ITER THROW
+ if (!emitAtomOp(cx->names().throw_, JSOP_CALLPROP)) // ITER RESULT EXCEPTION ITER THROW
return false;
- if (!emit1(JSOP_DUP)) // ITER RESULT EXCEPTION ITER THROW THROW
+ if (!emit1(JSOP_DUP)) // ITER RESULT EXCEPTION ITER THROW THROW
return false;
- if (!emit1(JSOP_UNDEFINED)) // ITER RESULT EXCEPTION ITER THROW THROW UNDEFINED
+ if (!emit1(JSOP_UNDEFINED)) // ITER RESULT EXCEPTION ITER THROW THROW UNDEFINED
return false;
- if (!emit1(JSOP_EQ)) // ITER RESULT EXCEPTION ITER THROW ?EQL
+ if (!emit1(JSOP_EQ)) // ITER RESULT EXCEPTION ITER THROW ?EQL
return false;
IfThenElseEmitter ifThrowMethodIsNotDefined(this);
- if (!ifThrowMethodIsNotDefined.emitIf()) // ITER RESULT EXCEPTION ITER THROW
+ if (!ifThrowMethodIsNotDefined.emitIf()) // ITER RESULT EXCEPTION ITER THROW
+ return false;
+ savedDepthTemp = stackDepth;
+ if (!emit1(JSOP_POP)) // ITER RESULT EXCEPTION ITER
+ return false;
+ // ES 14.4.13, YieldExpression : yield * AssignmentExpression, step 5.b.iii.2
+ //
+ // If the iterator does not have a "throw" method, it calls IteratorClose
+ // and then throws a TypeError.
+ if (!emitIteratorClose()) // ITER RESULT EXCEPTION
return false;
if (!emitUint16Operand(JSOP_THROWMSG, JSMSG_ITERATOR_NO_THROW)) // throw
return false;
- if (!ifThrowMethodIsNotDefined.emitEnd()) // ITER OLDRESULT EXCEPTION ITER THROW
+ stackDepth = savedDepthTemp;
+ if (!ifThrowMethodIsNotDefined.emitEnd()) // ITER OLDRESULT EXCEPTION ITER THROW
return false;
// ES 14.4.13, YieldExpression : yield * AssignmentExpression, step 5.b.iii.4.
- // RESULT = ITER.throw(EXCEPTION) // ITER OLDRESULT EXCEPTION ITER THROW
- if (!emit1(JSOP_SWAP)) // ITER OLDRESULT EXCEPTION THROW ITER
+ // RESULT = ITER.throw(EXCEPTION) // ITER OLDRESULT EXCEPTION ITER THROW
+ if (!emit1(JSOP_SWAP)) // ITER OLDRESULT EXCEPTION THROW ITER
return false;
- if (!emit2(JSOP_PICK, 2)) // ITER OLDRESULT THROW ITER EXCEPTION
+ if (!emit2(JSOP_PICK, 2)) // ITER OLDRESULT THROW ITER EXCEPTION
return false;
- if (!emitCall(JSOP_CALL, 1, iter)) // ITER OLDRESULT RESULT
+ if (!emitCall(JSOP_CALL, 1, iter)) // ITER OLDRESULT RESULT
return false;
checkTypeSet(JSOP_CALL);
- if (!emitCheckIsObj(CheckIsObjectKind::IteratorThrow)) // ITER OLDRESULT RESULT
+ if (!emitCheckIsObj(CheckIsObjectKind::IteratorThrow)) // ITER OLDRESULT RESULT
return false;
- if (!emit1(JSOP_SWAP)) // ITER RESULT OLDRESULT
+ if (!emit1(JSOP_SWAP)) // ITER RESULT OLDRESULT
return false;
- if (!emit1(JSOP_POP)) // ITER RESULT
+ if (!emit1(JSOP_POP)) // ITER RESULT
return false;
- MOZ_ASSERT(this->stackDepth == depth);
+ MOZ_ASSERT(this->stackDepth == startDepth);
JumpList checkResult;
- // Note that there is no GOSUB to the finally block here. If the iterator has a
- // "throw" method, it does not perform IteratorClose per
// ES 14.4.13, YieldExpression : yield * AssignmentExpression, step 5.b.ii.
- if (!emitJump(JSOP_GOTO, &checkResult)) // goto checkResult
+ //
+ // Note that there is no GOSUB to the finally block here. If the iterator has a
+ // "throw" method, it does not perform IteratorClose.
+ if (!emitJump(JSOP_GOTO, &checkResult)) // goto checkResult
return false;
- // IteratorClose logic.
if (!tryCatch.emitFinally())
return false;
- if (!emitDupAt(3)) // ITER RESULT FTYPE FVALUE ITER
+ // ES 14.4.13, yield * AssignmentExpression, step 5.c
+ //
+ // Call iterator.return() for receiving a "forced return" completion from
+ // the generator.
+
+ IfThenElseEmitter ifGeneratorClosing(this);
+ if (!emit1(JSOP_ISGENCLOSING)) // ITER RESULT FTYPE FVALUE CLOSING
+ return false;
+ if (!ifGeneratorClosing.emitIf()) // ITER RESULT FTYPE FVALUE
+ return false;
+
+ // Step ii.
+ //
+ // Get the "return" method.
+ if (!emitDupAt(3)) // ITER RESULT FTYPE FVALUE ITER
+ return false;
+ if (!emit1(JSOP_DUP)) // ITER RESULT FTYPE FVALUE ITER ITER
+ return false;
+ if (!emitAtomOp(cx->names().return_, JSOP_CALLPROP)) // ITER RESULT FTYPE FVALUE ITER RET
+ return false;
+
+ // Step iii.
+ //
+ // Do nothing if "return" is undefined.
+ IfThenElseEmitter ifReturnMethodIsDefined(this);
+ if (!emit1(JSOP_DUP)) // ITER RESULT FTYPE FVALUE ITER RET RET
+ return false;
+ if (!emit1(JSOP_UNDEFINED)) // ITER RESULT FTYPE FVALUE ITER RET RET UNDEFINED
+ return false;
+ if (!emit1(JSOP_NE)) // ITER RESULT FTYPE FVALUE ITER RET ?NEQL
+ return false;
+
+ // Step iv.
+ //
+ // Call "return" with the argument passed to Generator.prototype.return,
+ // which is currently in rval.value.
+ if (!ifReturnMethodIsDefined.emitIfElse()) // ITER OLDRESULT FTYPE FVALUE ITER RET
+ return false;
+ if (!emit1(JSOP_SWAP)) // ITER OLDRESULT FTYPE FVALUE RET ITER
+ return false;
+ if (!emit1(JSOP_GETRVAL)) // ITER OLDRESULT FTYPE FVALUE RET ITER RVAL
+ return false;
+ if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ITER OLDRESULT FTYPE FVALUE RET ITER VALUE
+ return false;
+ if (!emitCall(JSOP_CALL, 1)) // ITER OLDRESULT FTYPE FVALUE RESULT
+ return false;
+ checkTypeSet(JSOP_CALL);
+
+ // Step v.
+ if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ITER OLDRESULT FTYPE FVALUE RESULT
+ return false;
+
+ // Steps vi-viii.
+ //
+ // Check if the returned object from iterator.return() is done. If not,
+ // continuing yielding.
+ IfThenElseEmitter ifReturnDone(this);
+ if (!emit1(JSOP_DUP)) // ITER OLDRESULT FTYPE FVALUE RESULT RESULT
+ return false;
+ if (!emitAtomOp(cx->names().done, JSOP_GETPROP)) // ITER OLDRESULT FTYPE FVALUE RESULT DONE
+ return false;
+ if (!ifReturnDone.emitIfElse()) // ITER OLDRESULT FTYPE FVALUE RESULT
+ return false;
+ if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ITER OLDRESULT FTYPE FVALUE VALUE
+ return false;
+ if (!emitPrepareIteratorResult()) // ITER OLDRESULT FTYPE FVALUE VALUE RESULT
+ return false;
+ if (!emit1(JSOP_SWAP)) // ITER OLDRESULT FTYPE FVALUE RESULT VALUE
+ return false;
+ if (!emitFinishIteratorResult(true)) // ITER OLDRESULT FTYPE FVALUE RESULT
+ return false;
+ if (!emit1(JSOP_SETRVAL)) // ITER OLDRESULT FTYPE FVALUE
+ return false;
+ savedDepthTemp = this->stackDepth;
+ if (!ifReturnDone.emitElse()) // ITER OLDRESULT FTYPE FVALUE RESULT
+ return false;
+ if (!emit2(JSOP_UNPICK, 3)) // ITER RESULT OLDRESULT FTYPE FVALUE
+ return false;
+ if (!emitUint16Operand(JSOP_POPN, 3)) // ITER RESULT
+ return false;
+ {
+ // goto tryStart;
+ JumpList beq;
+ JumpTarget breakTarget{ -1 };
+ if (!emitBackwardJump(JSOP_GOTO, tryStart, &beq, &breakTarget)) // ITER RESULT
+ return false;
+ }
+ this->stackDepth = savedDepthTemp;
+ if (!ifReturnDone.emitEnd())
+ return false;
+
+ if (!ifReturnMethodIsDefined.emitElse()) // ITER RESULT FTYPE FVALUE ITER RET
+ return false;
+ if (!emit1(JSOP_POP)) // ITER RESULT FTYPE FVALUE ITER
return false;
- if (!emitIteratorClose(Some(tryStart))) // ITER RESULT FTYPE FVALUE
+ if (!emit1(JSOP_POP)) // ITER RESULT FTYPE FVALUE
+ return false;
+ if (!ifReturnMethodIsDefined.emitEnd())
+ return false;
+
+ if (!ifGeneratorClosing.emitEnd())
return false;
if (!tryCatch.emitEnd())
@@ -8338,7 +8372,7 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter, ParseNode* gen)
if (!emitCheckIsObj(CheckIsObjectKind::IteratorNext)) // ITER RESULT
return false;
checkTypeSet(JSOP_CALL);
- MOZ_ASSERT(this->stackDepth == depth);
+ MOZ_ASSERT(this->stackDepth == startDepth);
if (!emitJumpTargetAndPatch(checkResult)) // checkResult:
return false;
@@ -8349,10 +8383,12 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter, ParseNode* gen)
if (!emitAtomOp(cx->names().done, JSOP_GETPROP)) // ITER RESULT DONE
return false;
// if (!DONE) goto tryStart;
- JumpList beq;
- JumpTarget breakTarget{ -1 };
- if (!emitBackwardJump(JSOP_IFEQ, tryStart, &beq, &breakTarget)) // ITER RESULT
- return false;
+ {
+ JumpList beq;
+ JumpTarget breakTarget{ -1 };
+ if (!emitBackwardJump(JSOP_IFEQ, tryStart, &beq, &breakTarget)) // ITER RESULT
+ return false;
+ }
// result.value
if (!emit1(JSOP_SWAP)) // RESULT ITER
@@ -8362,7 +8398,7 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter, ParseNode* gen)
if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // VALUE
return false;
- MOZ_ASSERT(this->stackDepth == depth - 1);
+ MOZ_ASSERT(this->stackDepth == startDepth - 1);
return true;
}
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 78eb3510c..2ab6c6fef 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -679,9 +679,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
// Pops iterator from the top of the stack. Pushes the result of |.next()|
// onto the stack.
MOZ_MUST_USE bool emitIteratorNext(ParseNode* pn, bool allowSelfHosted = false);
- MOZ_MUST_USE bool emitIteratorClose(
- mozilla::Maybe<JumpTarget> yieldStarTryStart = mozilla::Nothing(),
- bool allowSelfHosted = false);
+ MOZ_MUST_USE bool emitIteratorClose(bool allowSelfHosted = false);
template <typename InnerEmitter>
MOZ_MUST_USE bool wrapWithDestructuringIteratorCloseTryNote(int32_t iterDepth,
diff --git a/js/src/tests/ecma_6/Generators/yield-star-iterator-close.js b/js/src/tests/ecma_6/Generators/yield-star-iterator-close.js
index ec62dd86d..91ad31cb6 100644
--- a/js/src/tests/ecma_6/Generators/yield-star-iterator-close.js
+++ b/js/src/tests/ecma_6/Generators/yield-star-iterator-close.js
@@ -6,6 +6,8 @@ function test() {
var returnCalledExpected = 0;
var nextCalled = 0;
var nextCalledExpected = 0;
+ var throwCalled = 0;
+ var throwCalledExpected = 0;
var iterable = {};
iterable[Symbol.iterator] = makeIterator({
next: function() {
@@ -25,9 +27,9 @@ function test() {
// G.p.throw on an iterator without "throw" calls IteratorClose.
var g1 = y();
g1.next();
- assertThrowsValue(function() {
+ assertThrowsInstanceOf(function() {
g1.throw("foo");
- }, "foo");
+ }, TypeError);
assertEq(returnCalled, ++returnCalledExpected);
assertEq(nextCalled, ++nextCalledExpected);
g1.next();
@@ -98,9 +100,18 @@ function test() {
// IteratorClose expects iter.return to return an Object.
var g6 = y();
g6.next();
- assertThrowsInstanceOf(function() {
+ var exc;
+ try {
g6.throw("foo");
- }, TypeError);
+ } catch (e) {
+ exc = e;
+ } finally {
+ assertEq(exc instanceof TypeError, true);
+ // The message test is here because instanceof TypeError doesn't
+ // distinguish the non-Object return TypeError and the
+ // throw-method-is-not-defined iterator protocol error.
+ assertEq(exc.toString().indexOf("non-object") > 0, true);
+ }
assertEq(returnCalled, ++returnCalledExpected);
// G.p.return passes its argument to "return".
@@ -115,6 +126,25 @@ function test() {
g7.next();
g7.return("in test");
assertEq(returnCalled, ++returnCalledExpected);
+
+ // If a throw method is present, do not call "return".
+ iterable[Symbol.iterator] = makeIterator({
+ throw: function(e) {
+ throwCalled++;
+ throw e;
+ },
+ ret: function(x) {
+ returnCalled++;
+ return { done: true };
+ }
+ });
+ var g8 = y();
+ g8.next();
+ assertThrowsValue(function() {
+ g8.throw("foo");
+ }, "foo");
+ assertEq(throwCalled, ++throwCalledExpected);
+ assertEq(returnCalled, returnCalledExpected);
}
test();
diff --git a/js/src/tests/ecma_6/shell.js b/js/src/tests/ecma_6/shell.js
index 4da9221d6..756da9f36 100644
--- a/js/src/tests/ecma_6/shell.js
+++ b/js/src/tests/ecma_6/shell.js
@@ -21,10 +21,11 @@
/** Make an iterator with a return method. */
global.makeIterator = function makeIterator(overrides) {
+ var throwMethod;
+ if (overrides && overrides.throw)
+ throwMethod = overrides.throw;
var iterator = {
- throw: function(e) {
- throw e;
- },
+ throw: throwMethod,
next: function(x) {
if (overrides && overrides.next)
return overrides.next(x);