Re: [Bug 23933] Proposal: Change constraints to use WebIDL dictionaries

On 12/06/2013 08:40 PM, Jan-Ivar Bruaroey wrote:
> On 12/6/13 11:56 AM, cowwoc wrote:
>> On 06/12/2013 2:59 AM, Jan-Ivar Bruaroey wrote:
>>>
>>> The only reason I can see to pick it would be to keep what I call 
>>> the footgun, the default behavior where webdevs who don't think 
>>> about the complicated unknown case, make apps that (perhaps 
>>> inadvertently) block everyone indiscriminately, including both 
>>> legitimate and illegitimate users, until a browser is upgraded with 
>>> a new constraint. Since the webdev can flip the default and the user 
>>> cannot, I think we should default to the way that doesn't block the 
>>> user. I already have evidence that webdevs aren't thinking ahead 
>>> when they use mandatory.
>>>
>>
>> I almost understand this point, but not quite yet. Can you please 
>> give a concrete example/scenario of this taking place?
>
> I already included https://bugzilla.mozilla.org/show_bug.cgi?id=927358 
> which shows the footgun. The introduction of getGumKnownConstraints() 
> will not cure this syndrome, since the footgun is what happens by 
> default for people who do NOT bother or know the right procedure of 
> calling getGumKnownConstraints() to handle unknowns properly.

Just FTR, I totally disagree that the behaviour shown in this Mozilla 
bug is a footgun.

What happened with this bug is that the user relied on behaviour that 
was not supported. Failing early with a clear error is exactly the 
behaviour we should have.

Letting the user specify a mandatory constraint, having it ignored 
because it's not implemented yet, letting the user depend on the fact 
that his app works despite a nonsatisfiable constraint, having the 
constraint implemented in a later version, and THEN blowing away his app 
- that is the more dangerous footgun.

Mozilla's fix is wrong, and should be reverted.