Function constrain_virtual_equals_external 

pub fn constrain_virtual_equals_external<F: Field + Ord>(
    region: &mut Region<'_, F>,
    virtual_cell: AssignedValue<F>,
    external_cell: Cell,
    copy_manager: &mut CopyConstraintManager<F>,
)

Constrains that virtual_cell is equal to external_cell. The virtual_cell must have already been raw assigned with the raw assigned cell stored in copy_manager unless it is marked an external-only cell with type id EXTERNAL_CELL_TYPE_ID.

• When the virtual cell has already been assigned, the assigned cell is constrained to be equal to the external cell.
• When the virtual cell has not been assigned and it is marked as an external cell, it is assigned to external_cell and the mapping is stored in copy_manager.

This should only be called when witness_gen_only is false, otherwise it will panic.

Panics

If witness generation only mode is true.