No MDL form binds the Image widget to an image object; dynamicimage fails CE0582 in React apps #1476

Summary

A React-client app cannot show an image that a user uploaded (a System.Image object) through MDL:

• The pluggable Image widget (com.mendix.widget.web.image, v1.5.0) shows an image object through its imageObject property. MDL can only point that property at an image-collection entry (Image: 'Module.Collection.Name'), so there is no way to bind it to the object in context.
• The legacy dynamicimage writes a valid model since Selectionhelper with renderStyle: 'custom' — slot children containing StaticImageViewer are not re-executable; workaround requires placeholder dynamictext #1057, but a React-client app refuses it with CE0582.

So MDL has no form that shows an uploaded photo on a page in a Mendix 11 React-client app.

Reproduction

Measured with mxcli v0.26.0, Mendix 11.12.1, on a new app (React client, the default):

mdl 1;
create persistent entity MyFirstModule.Photo extends System.Image (
  Caption: String(200)
);
create or modify page MyFirstModule.Photo_View (Title: 'Photo', Layout: Atlas_Core.PopupLayout,
                                               Params: ($Photo: MyFirstModule.Photo)) {
  dataview Photo_View_Form (DataSource: $Photo) {
    image Photo_View_Image ()   -- variant A, B or C below
  }
};

Notes:

• Variant B is not a dynamic image. dynamicImage is not one of the widget's datasource values, which are image, imageUrl and icon in Image.xml. mxcli accepts and stores the unknown value without a warning, and the build passes. I did not check what it renders, but it cannot be bound to the object either. Rejecting an unknown enumeration value at check time would have saved an agent several attempts.
• The widget's own definition says the dynamic case exists. imageObject is of type image, which Studio Pro lets you set to a static image or to the image object in context, and defaultImageDynamic is described as "the image that is displayed if no image is uploaded".
• mxcli syntax page widgets names the three sources MDL supports: a collection image, imageUrl and icon.

What an agent does instead

An agent building a product catalogue with uploaded photos spent about six minutes on variants A to C, then worked around it:

1. a JavaScript action computes the image's URL with mx.data.getDocumentUrl and mx.data.getImageUrl;
2. the URL is stored in a new String attribute on the entity;
3. an image (ImageType: imageUrl, ImageUrl: '{1}', ...) shows it.

That works, but it adds an attribute to the domain model only to carry a URL that depends on the object's change date, and every agent has to rediscover it.

Expected

An MDL form that binds the Image widget's imageObject to the image object in context, for example the data view's object or an association path to a System.Image specialisation. It would also need describe page to print it back, and defaultImageDynamic as the fallback image.

A Studio Pro-authored sample of the dynamic imageObject binding would pin the BSON shape. The legacy dynamicimage fix noted that a blank 11.12.1 app has none, so the sample has to come from a page made in Studio Pro.