I used QGIS 2.18 and now I use QGIS 3.0 under Windows 10 in Spanish versions.
In the field editor in version 2.18 each field had his button "Text edition" but in version 3.0 that button doesn't appear. In the next images you can see what I mean, the first is from version 2.18 and the second is from version 3.0.
Can someone help me? Have they moved that option to another window?