518621 - JS_ReportErrorNumber ignores exception type for user-generated messages

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

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So, you're supposed to be able to construct your own JSErrorFormatString, consisting of { format, count, exception }, which JS_ReportErrorNumber() fetches via your own defined my_GetErrorMessage() function. However, what it really does is compare whether the supplied fnptr is js_GetErrorMessage():

http://mxr.mozilla.org/mozilla-central/source/js/src/jscntxt.cpp#1421

and does localization stuff etc. It seems to get this part wrong. It uses the format and count just fine, but uses the exception type from http://mxr.mozilla.org/mozilla-central/source/js/src/js.msg. So, if I want a TypeError, I have to make my error number 3.

This, while being somewhat amusing, is also pretty bizarre.

Comment 1

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Attachment: patch v1

This is the minimal fix; it propagates the callback fnptr into js_ErrorToException so it can do a proper lookup of the exception type, instead of assuming js_GetLocalizedErrorMessage.

I thought about doing a more extensive fix. The problem is really that JSErrorReport (https://developer.mozilla.org/en/SpiderMonkey/JSAPI_Reference/JSErrorReport) has an errorNumber field, but that means nothing without a callback to go with it. But this is part of JSAPI and is used by user error reporters and debug hooks, so they're probably already assuming that errorNumber corresponds to a jsengine error in js.msg. We could perhaps add an exnType field, which either gets hardcoded to the right value (for jsengine errors) or filled in by js_ExpandErrorArguments when it calls the callback.

Comment 2

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http://hg.mozilla.org/mozilla-central/rev/760590721612