[FIX] purchase_stock: consider product unit price precision

When changing the product price precision, this can lead to incorrect
stock valuations.

To reproduce the error:
(Enable debug mode)
1. Go to Settings > Technical > Database Strucutre > Decimal Accuracy
2. Edit Product Price:
    - Digits: 4
3. Create a Product Category PC:
    - Costing Method: FIFO
4. Create a Product P:
    - Product Type: Storable Product
    - Product Category: PC
5. Create a RfQ with product P:
    - Quantity: 1000
    - Unit Price: 0.035
6. Confirm Order, Receive Products, Validate
7. Click on Valuation

Error: The total value is equal to $40 instead of $35. The calculation
was done after rounding the unit price: $0.035 becomes $0.04, then
1000*0.04=$40.

When confirming the RfQ, a stock move is created. To do so, the method
`_get_stock_move_price_unit` is called. When validating the delivery, it
recomputes the unit price thanks to method `_get_price_unit`. In both
situation, and if the line has taxes, the method `compute_all` is called
like this:
```python
price_unit = line.taxes_id.with_context(round=False).compute_all(price_unit,
	currency=line.order_id.currency_id, quantity=1.0)['total_void']
```
But here is the problem. In this method, total amount is computed with
this line:
```python
base = currency.round(price_unit * quantity)
```
However, `quantity` is equal to 1 and the multiplication is rounded
using the currency precision. As a result, `base` is equal to $0.04.
Then, all computations will use this value and will be incorrect.

This fix applies the real quantity so `base` will have the correct
value:
```
base = currency.round(price_unit * quantity)
     = currency.round(0.035 * 1000)
     = 35
```

OPW-2472192

closes odoo/odoo#70080

X-original-commit: a57dc07189c15296055d6a07ca6d0bd350c4f11a
Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/addons/purchase_stock/tests/test_fifo_price.py b/addons/purchase_stock/tests/test_fifo_price.py
index 8125bf65715..848d967c7bf 100644
--- a/addons/purchase_stock/tests/test_fifo_price.py
+++ b/addons/purchase_stock/tests/test_fifo_price.py
@@ -319,3 +319,48 @@ class TestFifoPrice(ValuationReconciliationTestCommon):
         original_out_move = outgoing_shipment_neg.move_lines[0]
         self.assertEqual(original_out_move.product_id.value_svl,  12000.0, 'Value of the move should be 12000')
         self.assertEqual(original_out_move.product_id.qty_available, 150.0, 'Qty available should be 150')
+
+    def test_01_test_fifo(self):
+        """" This test ensures that unit price keeps its decimal precision """
+
+        unit_price_precision = self.env['ir.model.data'].xmlid_to_object('product.decimal_price')
+        unit_price_precision.digits = 3
+
+        tax = self.env["account.tax"].create({
+            "name": "Dummy Tax",
+            "amount": "0.00",
+            "type_tax_use": "purchase",
+        })
+
+        super_product = self.env['product.product'].create({
+            'name': 'Super Product',
+            'type': 'product',
+            'categ_id': self.stock_account_product_categ.id,
+            'standard_price': 0.035,
+        })
+        self.assertEqual(super_product.cost_method, 'fifo')
+        self.assertEqual(super_product.valuation, 'real_time')
+
+        purchase_order = self.env['purchase.order'].create({
+            'partner_id': self.env.ref('base.res_partner_3').id,
+            'order_line': [(0, 0, {
+                'name': super_product.name,
+                'product_id': super_product.id,
+                'product_qty': 1000,
+                'product_uom': super_product.uom_id.id,
+                'price_unit': super_product.standard_price,
+                'date_planned': time.strftime('%Y-%m-%d'),
+                'taxes_id': [(4, tax.id)],
+            })],
+        })
+
+        purchase_order.button_confirm()
+        self.assertEqual(purchase_order.state, 'purchase')
+
+        picking = purchase_order.picking_ids[0]
+        res = picking.button_validate()
+        Form(self.env[res['res_model']].with_context(res['context'])).save().process()
+
+        self.assertEqual(super_product.standard_price, 0.035)
+        self.assertEqual(super_product.value_svl, 35.0)
+        self.assertEqual(picking.move_lines.price_unit, 0.035)