`has_image_size()` returns false for Core image sizes

[desrosj]

has_image_size() returns false (does not exist) for the four core image sizes (thumbnail, medium, medium_large, large).

get_intermediate_image_sizes() returns these core image sizes merged with custom registered sizes through add_image_size().

has_image_size() should return true for the core image sizes, or the function docs should note that the core image sizes are not checked in the function.

[subrataemfluence]

has_image_size() function is specifically used for image sizes that are registered via add_image_size() function. It is actually using wp_get_additional_image_sizes() function, which does not consider core image sizes.

On the other hand get_intermediate_image_sizes() uses the same function (wp_get_additional_image_sizes()) but it forcefully defines an array of core image sizes and merges it with the array returned by wp_get_additional_image_sizes() function.

I agree with @desrosj that the documentation has to be more clear about the limitation.

I have edited description at ​https://codex.wordpress.org/Function_Reference/has_image_size

[NathanAtmoz]

Introduce second parameter to has_image_size() to use core image sizes and update docs.

[kirasong]

I suspect this will need some research to find out the effects for backcompat on each way of fixing this, and how much a param will help. After a chat in #core-media about it, @desrosj offered to do some digging.

[andizer]

Added two simple tests

[desrosj]

This still needs some research and falls outside of the 5.0 focus. Punting to 5.1.

[desrosj]

@andizer thanks for those tests! More code would need to be added for the second one to be accurate, though, as has_image_size() does not currently accept a second parameter.

I am going to punt this to Future Release. This could just be a simple docs change to indicate core image sizes are excluded, or an added parameter. But the implications of the second option are not yet clear.

Trac ticket: #43046