887521 - Differential Testing: Different error message involving Object.preventExtensions

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

Object.preventExtensions = 1
function f() {
    Object.preventExtensions()
}
for each(w in [0, 0]) {
    try {
        f()
    } catch (e) {
        print(e)
    }
}

shows the following on a 64-bit deterministic threadsafe js shell on m-c rev 61c3c8b85563:

TypeError: undefined is not a function
TypeError: undefined is not a function

but shows the following with --ion-eager:

TypeError: undefined is not a function
TypeError: 1 is not a function


This seems to be an old bug. Setting needinfo for jandem as this may cloud other correctness bugs.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Patch

When js::OnUnknownMethod does not find a __noSuchMethod__ property, it sets vp (the result of the CALLPROP) to the result of the __noSuchMethod__ lookup. This makes no sense to me and the patch changes it to not touch vp in that case.

This means if you do:

Object.foo = 1;
Object.foo();

The error now says "1 is not a function" instead of "undefined is not a function". This only happens in more-deterministic shells though, in normal shells the expression decompiler turns it into "Object.foo is not a function" so it's hard to add a testcase for this.

Comment 2

[Jesse Ruderman]

You could make a test whose skip or expected depends on 
getBuildConfiguration()["more-deterministic"]

Comment 3

[Jeff Walden [:Waldo]]

Comment on attachment 768274 [details] [diff] [review]
Patch

Review of attachment 768274 [details] [diff] [review]:
-----------------------------------------------------------------

wat

Comment 4

[Jan de Mooij [:jandem]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/911c3a79cefa

(In reply to Jesse Ruderman from comment #2)
> You could make a test whose skip or expected depends on 
> getBuildConfiguration()["more-deterministic"]

Last time I tested it, more-deterministic shells fail various tests (enumeration order etc?) and nobody will notice if it breaks, so I didn't bother.

Comment 5

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/911c3a79cefa