Gutenberg: Only baseline $content_width is used for images

[laurelfulford]

In Calypso, the block-based editor uses the theme's $content_width to set a size for images. But some themes have different $content_widths based on context (like certain templates, or when a sidebar isn't present); only the default one is used.

This differs from using the editor on a self-hosted site, where the default size is 1024px wide (the large image size); it may not be wide enough to cover all cases, but it is generally wider than most theme's $content_width.

It seems like a similar underlying issue to #29296, where the $content_width is also an issue when switching themes.

Steps to reproduce

1. Start with a theme that sets multiple $content_widths -- Button 2 is one example. Its default $content_width is 663, but it's upped to 982 when the full-width template is used on a page, or there is no sidebar.
2. Make sure there are no sidebar widgets.
3. Insert an image block into the editor; note the size.
4. Publish the post, and note the size.

What I expected

The image to fill the available space, both in the editor and on the front-end.

What happened instead

The image defaulted to the theme's main $content_width, rather than the one set on the page's template.

For Button 2, we can "hide" the issue by decreasing the editor width to 663 -- right now it uses the wider content width -- but the image will still be too narrow on publish.

The current work-around is manually adjusting the image size in the block options.

I understand work is still being done in the editor on image sizing. In the meantime, is it possible to use the widest $content_width present in a theme, or default to the "Large" image size instead?

Screenshot / Video

Image added to the editor:

Published version of post:

Context / Source

This was originally reported as an issue for Twenty Twelve (Automattic/themes#422); it could be reproduced in Sketch, and also came up when fixing another issue in Button 2.

[mmtr]

No longer reproducible after removing Gutenberg on Calypso in favor of #31196.