Focusing too much on the call site is probably misleading, which is why most production-quality immediate-mode UI libraries generally don't rely on __FILE__/__LINE or stack walks or anything else like that. The issue isn't just loops. As soon as you wrap code in a function for reuse, the proximate call site no longer has anything to do with the widget ID; in the extreme case, your entire immediate-mode UI is data driven and there's nothing in the code paths that indicate anything at all about the widget IDs.
The real hack is implicit IDs, not the ID stack (which is just a way of implementing a hierarchical namespace like file system paths or URLs). Implicit IDs just work 99% of the time and rarely require manual intervention, so seeking a 100% solution is a tempting siren song. But once you actually start writing UIs like this, the 99% solution is just fine.
The real hack is implicit IDs, not the ID stack (which is just a way of implementing a hierarchical namespace like file system paths or URLs). Implicit IDs just work 99% of the time and rarely require manual intervention, so seeking a 100% solution is a tempting siren song. But once you actually start writing UIs like this, the 99% solution is just fine.