CommonsMetadata should not ignore book templates if they are no other information templates on the page
completed by: Geoffrey Mon
mentors: Gergő Tisza
File pages use a set of templates (Information, Artwork, Photograph, Book) to provide machine-readable author information. CommonsMetadata currently ignores Book templates because the machine-readable author names they provide are usually not really authors; but this behavior is wrong when Book is the only source of author information on the page (in that case, the image is typically *about* the book, not just *from* the book, and the book author should be displayed in the image credits).
CommonsMetadata should use the information from a Book template iff it is the only info template on the page (per TemplateParser::$infoTemplateClasses).
This is T74084 (reopened) in Wikimedia's issue tracker.
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