Thanks for the comment. I've found a way to implement [LenientThis] using existing V8 APIs. (But still think it would be better to support it in V8). I've prepared a CL to support [LenientThis] here: https://codereview.chromium.org/1161463009/
For the idea to use a wrapper function, the type check is done before a callback function is called, so anyway, we need to disable V8's type check. I think the type check is done at: https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/builtins.cc&l=1078 I figured out that the type check is done based on v8::Signature of v8::FunctionTemplate. So, V8 already has a feature to disable the type check. If we specify the empty signature, V8 doesn't do the type check. (I didn't know that.) Having said that, I think it would be much better if V8 directly supported [LenientThis], because disabling the type check means that there is no guarantee what FunctionCallbackInfo::Holder() points to. We have to carefully avoid using FunctionCallbackInfo::Holder(). This is a security risk for us. My expectation is: - Blink specifies a FunctionTemplate as [LenientThis] and gives the appropriate Signature even if [LenientThis]. - V8 always tries to find the right receiver in FunctionTemplateInfo::GetCompatibleReceiver - if failed and not [LenientThis], throw a TypeError as same as now - if failed and [LenientThis], just return undefined. Then, FunctionCallbackInfo::Holder() always points to the appropriate holder. Cheers, Yuki Shiino 2015-06-04 16:56 GMT+09:00 Ben L. Titzer <[email protected]>: > Is it possible to emulate these semantics with a wrapper function that > catches type errors at the API boundary? > > On Thu, Jun 4, 2015 at 4:12 AM, Yuki Shiino <[email protected]> > wrote: > >> +cc: [email protected] >> -cc: v8-team >> >> Sorry, changed the mailing list to v8-users. >> >> Cheers, >> Yuki Shiino >> >> >> 2015-06-03 22:20 GMT+09:00 Yuki Shiino <[email protected]>: >> >>> Hi V8 team, >>> >>> It turned out that we need to support [LenientThis] extended attribute >>> <http://heycam.github.io/webidl/#LenientThis> sometime soon to keep the >>> backward compatibility. Here are the issues that need [LenientThis]. >>> https://crbug.com/472260 >>> https://crbug.com/492820 >>> >>> Since the type checking of instances is done in V8, we need you guys' >>> help to relax the type checking against |this|. Could you guys help us to >>> support [LenientThis]? >>> >>> The required behavior of [LenientThis] is >>> - get: returns |undefined| if the type checking fails, instead of >>> throwing TypeError. >>> - set: does nothing if the type checking fails, instead of throwing >>> TypeError. >>> >>> My expectation is >>> - V8 provides an option to relax the type checking >>> - V8 handles the required behavior above, or >>> V8 calls Blink binding code back even if the type doesnt match. >>> Any other ideas are welcome. >>> >>> Cheers, >>> Yuki Shiino >>> >>> >> -- >> -- >> v8-team mailing list >> [email protected] >> https://groups.google.com/a/google.com/group/v8-team >> > > -- -- v8-users mailing list [email protected] http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
