[wp-trac] [WordPress Trac] #38558: Customizer assigns invalid values to header_image_data theme mod during preview

[WordPress Trac]

#38558: Customizer assigns invalid values to header_image_data theme mod during
preview
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 Reporter:  bradyvercher  |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:  3.9
 Severity:  normal        |   Keywords:
  Focuses:                |
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 Some background: The custom header feature uses two theme mods to store
 data: `header_image` and `header_image_data`. These are kept in sync by
 routing everything through `Custom_Header_Image::set_header_image()`,
 which transforms the data as needed before saving.

 Looking at that method, these are the values that can exist for each:

 * `header_image`: Can have the URL to an image, `remove-header`, `random-
 default-image`, or `random-uploaded-image`.
 * `header_image_data`: Always contains an object with header properties.
 At a minimum, it should have a `url` and `thumbnail_url` property, but may
 contain additional data.

 This is difficult to demonstrate in a default theme right now since most
 use `get_header_image()` and manually construct an image tag, which uses
 the `header_image` mod. However `the_header_image_tag()` and
 `the_custom_header_markup()` end up relying on `get_custom_header()`,
 which uses the `header_image_data` theme mod. So when an unrecognized
 value is passed from the Customizer, default headers end up not displaying
 at all in the preview.

 To reproduce:

 1. Switch to Twenty Ten
 2. Open `twentyten/header.php` and replace the header image markup with
 `the_header_image_tag()`
 3. Access the Customizer and open the "Header Image" section
 4. Choose one of the "Suggested" headers

 Notice that the header image doesn't display in the preview.

 Type `wp.customize( 'header_image_data' )()` in the JS console and notice
 that the value is a string identifier for the image. When changes are
 saved in the Customizer, that value does get converted to the expected
 object so everything works when viewing the front end, but the preview
 will be broken.

 This will eventually become more noticeable as themes begin using
 `the_header_image_tag()` for responsive header images or
 `the_custom_header_markup()` for video headers.

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Ticket URL: <https://core.trac.wordpress.org/ticket/38558>
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