1052417 - Default `sizes` attribute value for `srcset` should be 100vw

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Remi]

Attachment: srcset-nosizes.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36

Steps to reproduce:

On the current version of Firefox Nightly (34.0a1), make sure to activate the flags for responsive images with `srcset`. (Go to about:config and set `dom.image.srcset.enabled` and `dom.image.picture.enabled` to true.)

Open a page with an <img> with srcset attribute with various images. For example the following : 

<img src="http://i.imgur.com/pnUUCFQ.png" srcset="http://i.imgur.com/35cz49W.png 480w, http://i.imgur.com/X7vSnQV.png 640w, http://i.imgur.com/JqqqI8g.png 1440w" />


Actual results:

No matter the window resolution, the first image of the `srcset` list is always shown. Other images of the `srcset` list are never visible.


Expected results:

Correct images depending of the window resolution should be shown. This actually works if you had a `sizes` attribute with a `100vw` value. 

But the specification clearly states that the default value for `sizes` is `100vw` and that in this case, the attribute could be omitted. See http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#the-picture-element

Comment 1

[:Gijs (out for now; he/him)]

John, can you have a look?

Comment 2

[John Schoenick [:johns]]

Attachment: Don't bailout of sizes selection if sizes wasn't provided

This was incompletely updated -- we use 100vw as a default, but reject sizes-using candidates if we had no attribute per an earlier spec. Just removing that bailout works as expected.

The picture tests in Bug 1023519 will cover this

Comment 3

[John Schoenick [:johns]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9b7fce122203

Try:
https://treeherder.mozilla.org/ui/#/jobs?repo=try&revision=8af04bb0dc51

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/9b7fce122203