The code in my local machine (to be commited later) refers to the main window UI class as EchidnaEditor, although the ui file still uses MainWindow, Qt Designer's default class name.
I was confused so much by the error message, until I realized the issue was this.
Anyways, this includes the "fix the sidebar tab that isn't a proper tab". Should have commited this in a separate commit, but Git won't let me.
Should have commited this earlier. Same thing with e0ba34d.
Ugh, should have commited this before making the next commit.
Why I still do this sort of stuff. Echidna is supposed to be more maturely developed than BLThunderstorm.
God help me.
Anyways, the diff for the new file ui/echidna.ui is not included here because of that.