[Webkit-unassigned] [Bug 157872] Our parser doesn't properly parse default parameter expressions in a class method

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sun May 29 23:08:02 PDT 2016


Caio Lima <ticaiolima at gmail.com> changed:

           What    |Removed                     |Added
                 CC|                            |ticaiolima at gmail.com

--- Comment #2 from Caio Lima <ticaiolima at gmail.com> ---
Hello guys, It is a RFC.

I created a test case based on the Saam's sample:

class C {
  constructor() { this._x = 45; }
  get foo() { return this._x;}

class D extends C {

  x(y = () => super.foo) {
    return y();

if ((new D).x() === 45) {
} else {

I tested it in V8 and SpiderMonkey and they parsed and executed correctly. So, I decided to investigate the problem.

I tested the following workaround to find the reason of failing

class D extends C {

  x(y) {
    y ||= () => super.foo;
    return y();

And it worked. I noticed that the failing point was the following test present in Parser.cpp::parseMemberExpression():

if (!m_lexer->isReparsingFunction()) {
                SuperBinding functionSuperBinding = !functionScope->isArrowFunction() && !closestOrdinaryFunctionScope->isEvalContext()
                    ? functionScope->expectedSuperBinding()
                    : closestOrdinaryFunctionScope->expectedSuperBinding();
                semanticFailIfTrue(functionSuperBinding == SuperBinding::NotNeeded, "super is not valid in this context");

In the first test case, the "closestOrdinaryFunctionScope->expectedSuperBinding()" returned "SuperBinding::NotNeeded" and in the second case the return was "SuperBinding::Needed". I thought it was strange, since the "closestOrdinaryFunctionScope" in both cases should be in the same configuration. I debugged the parsing phase and noticed that "closestOrdinaryFunctionScope->m_expectedSuperBinding" was not being set before "parseFunctionParameters" in "Parser<LexerType>::parseFunctionInfo" (Parser.cpp).

In my patch proposal, I am setting "functionScope->setExpectedSuperBinding(expectedSuperBinding)" before call "parseFunctionParameters" in Parser.cpp:2019 as a proof of concept, however, I think it should be placed in the first 13 lines of the "Parser<LexerType>::parseFunctionInfo" function, since there are others "parseFunctionParameters" above the current modification. What do you think?

Also, I would like to know where I should can create a test case for this case.

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