Blender version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-03 19:00, hash: rBd62a749fcf48
In the shader editor, click on the dropdown to pick slot - it appears always fixed width, and long slot names cannot be easily seen:
https://i.imgur.com/wGFoIs6.jpg
Compare this to the image selector just next to the slots one - it is a lot wider and fits long filenames.