Add layout templates based on Panels layouts to core

We discussed this issue with @Bojhan, @yoroy, @Dries, and @Gábor today on the Ideas Queue review meeting.

Because the layouts represented here are copying an existing pattern from contrib that seems to have been successful since 2009, this seems like a great starting point for addressing the "must-have." If we decide we want more/fewer later, this is something that could be changed in a subsequent patch. The higher priority would be to improve the user experience of the layout selection (e.g. with visuals) vs. trying to get the list 100% right.

IMO these should live in layout module.

Agree with #5 could we keep a sub-module of layout_discovery to keep the layouts?

//Naveen

Eventually layout_discovery.module will go away and everything will live in the system.module (since subsystems cannot provide template files).

Right now there's not any right place to keep it in any module.
1) layout_discovery - getting merged into the system.module after layout_discovery reaches beta and then removed?
2) field_layout: We need to made other modules dependent on it if we'll keep it here
How about a separate module for keeping these layouts? Thoughts?
//Naveen

UI proposal:

https://www.drupal.org/files/issues/Add%20layouts%20states.png

For smaller screens, wrap the listing of layout icons:

https://www.drupal.org/files/issues/Add%20layouts%20small%20screen.png

Here we go,

Working on it.

Worked a bit on #14.

I was a bit in a hurry when I submitted the patch, so the replaces all the 'panel' and 'panel-' classes from templates and css-files with layout-discovery prefixed classes. I was a bit unsure about the naming of as good example on 3col 25-50-25 layout about the naming of the 25% parts. In responsive design sidebar is a wrong term and the same applies for narrow-column as all the three columns are probably 100% width on mobile.

Since layout_discovery and field_layout are alpha experimental modules, this issue should be eligible for 8.3.x according to our experimental module policy.

Right now the columns don't break for mobile widths, they stay at the same percentage width for all screen sizes. That's something we need to fix in Panels too, but probably should fix here before the layouts go in core. I can fix them tomorrow if no one else gets to it first.

I was thinking about fixing and cleaning up the whole CSS, but I think that it should be done on separate issue as it might require some conceptual discussion.

Reviewed the patch from #23 and it's RTBC from my point of view. It moves five out of eight panels layouts to layout_discovery -module, changes the naming to what has been spoken, it's working and the code has been written according the standards.

Leaving it still to needs work as my previous comment for #27 probably needs other opinions too.

Ok, that works. I think it's fine to have a follow up tickets for the CSS. Otherwise, this looks great to me.

@tim.plunkett gave me a mini crash course in Panels layouts to review this. This patch does three things things:

1. Moves the layouts from field_layout to layout_discovery so they are available to any implementing module. +1!
2. Adds Panels' layouts, also to layout_discovery, but drops the "stacked" naming convention in favor of simpler names.
3. Updates the existing twocol template to match the Panels version (adjusting tests as needed), with top and bottom regions available and slightly different CSS:
   

   

I agree with having #2852608: Review layout CSS and markup as a must-have followup; thank you for adding that.

Committed to 8.4.x and backported to 8.3.x as an API addition to an alpha experimental module. Also tagging for the release notes; we will mention this on the RC notes and add a small mention of it as a feature of layout discovery in the 8.3.0 release notes. Thanks!