I am an English assistant and I often hear my non-native students say:
I often buy fruits when I go to the supermarket.
I think it is wrong logically because "go" means "to move or travel from one place to another" (source). I am not sure whether it implies "you are already there"
Should we change to:
I often buy fruits when I am at the supermarket
but it does not say that "I go to the supermarket".
How do native speakers express that idea?
Note: when could mean "after", so, I often buy fruits when I go to the supermarket=I often buy fruits after I go to the supermarket