Function prepare_generated_column 

pub fn prepare_generated_column(
    context: &SchemaBindingContext<'_, '_>,
    qualifier: &str,
    snapshot: &[ColumnDef],
    columns: &mut [ColumnDef],
    index: usize,
    foreign_keys: &[ForeignKey],
) -> Result<(), SQLError>

Validate and bind the generation expression of columns[index], if it has one, against the relation’s columns as snapshot describes them before any of their expressions was bound.