[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 #69297

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

addons/purchase_stock/models/purchase.py

@@ -2,7 +2,7 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from odoo import api, fields, models, _
-from odoo.tools.float_utils import float_compare
+from odoo.tools.float_utils import float_compare, float_round
 from dateutil import relativedelta
 from odoo.exceptions import UserError
 
@@ -345,10 +345,13 @@ def _get_stock_move_price_unit(self):
         line = self[0]
         order = line.order_id
         price_unit = line.price_unit
+        price_unit_prec = self.env['decimal.precision'].precision_get('Product Price')
         if line.taxes_id:
+            qty = line.product_qty or 1
             price_unit = line.taxes_id.with_context(round=False).compute_all(
-                price_unit, currency=line.order_id.currency_id, quantity=1.0, product=line.product_id, partner=line.order_id.partner_id
+                price_unit, currency=line.order_id.currency_id, quantity=qty, product=line.product_id, partner=line.order_id.partner_id
             )['total_void']
+            price_unit = float_round(price_unit / qty, precision_digits=price_unit_prec)
         if line.product_uom.id != line.product_id.uom_id.id:
             price_unit *= line.product_uom.factor / line.product_id.uom_id.factor
         if order.currency_id != order.company_id.currency_id:

addons/purchase_stock/models/stock.py

@@ -2,6 +2,7 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from odoo import api, fields, models, _
+from odoo.tools.float_utils import float_round
 
 
 class StockPicking(models.Model):
@@ -36,11 +37,14 @@ def _get_price_unit(self):
         """ Returns the unit price for the move"""
         self.ensure_one()
         if self.purchase_line_id and self.product_id.id == self.purchase_line_id.product_id.id:
+            price_unit_prec = self.env['decimal.precision'].precision_get('Product Price')
             line = self.purchase_line_id
             order = line.order_id
             price_unit = line.price_unit
             if line.taxes_id:
-                price_unit = line.taxes_id.with_context(round=False).compute_all(price_unit, currency=line.order_id.currency_id, quantity=1.0)['total_void']
+                qty = line.product_qty or 1
+                price_unit = line.taxes_id.with_context(round=False).compute_all(price_unit, currency=line.order_id.currency_id, quantity=qty)['total_void']
+                price_unit = float_round(price_unit / qty, precision_digits=price_unit_prec)
             if line.product_uom.id != line.product_id.uom_id.id:
                 price_unit *= line.product_uom.factor / line.product_id.uom_id.factor
             if order.currency_id != order.company_id.currency_id:

addons/purchase_stock/tests/test_fifo_price.py

@@ -315,3 +315,52 @@ def test_00_test_fifo(self):
         original_out_move = outgoing_shipment_neg.move_lines[0]
         self.assertEquals(original_out_move.product_id.value_svl,  12000.0, 'Value of the move should be 12000')
         self.assertEquals(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 """
+
+        self._load('account', 'test', 'account_minimal_test.xml')
+        self._load('stock_account', 'test', 'stock_valuation_account.xml')
+
+        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.env.ref('product.product_category_1').id,
+            'standard_price': 0.035,
+        })
+        super_product.categ_id.property_cost_method = 'fifo'
+        super_product.categ_id.property_valuation = 'real_time'
+        super_product.categ_id.property_stock_account_input_categ_id = self.ref('purchase.o_expense')
+        super_product.categ_id.property_stock_account_output_categ_id = self.ref('purchase.o_income')
+
+        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]
+        self.env['stock.immediate.transfer'].create({'pick_ids': [(4, picking.id)]}).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)