The Emacs Widget Library: A Critique and Case Study

Summary

The Emacs widget library (widget.el and wid-edit.el) has been part of Emacs since 1996, when Per Abrahamsen wrote it to power the Customize interface. Nearly three decades later, it remains the foundation for M-x customize and appears in various packages that need form-like interfaces. It's also largely unchanged, rarely discussed, and - when you actually try to build something non-trivial with it - surprisingly painful to work with. This post is a critique born from experience. I've built complex UIs using the widget library, including a table widget with editable cells that reflows dynamically. The code lives in widget-extra, a library I wrote to extend the built-in widget system. It works. It was hard. The process revealed both the library's hidden power and its fundamental limitations. #1What It Does Well Before the critique, credit where it's due. #2Deep Integration with Emacs Widgets are text. They live in buffers, use overlays and text properties, and work identically in GUI and terminal Emacs. This is philosophically aligned with Emacs's core principle: everything is a buffer. You can use standard navigation, search the buffer, even run keyboard macros across widget forms. #2Performance A buffer with hundreds of widgets remains snappy. There are no heavy GUI objects, no separate rendering pipeline - just text with properties. The Customize interface, with its deeply nested groups and countless options, demonstrates this well. #2Type Hierarchy The library excels at defining what widgets are. You can create new widget types that inherit from existing ones, override specific behaviours, and build a taxonomy of components. A bounded-int-field can inherit from int-field which inherits from field which inherits from default. This is genuinely powerful for building families of related widgets. That said, this is a classical inheritance approach, and the game development community moved away from deep inheritance hierarchies years ago. The Entity-Component-System pa...