[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>

3 files changed, 55 insertions, 3 deletions

diff --git a/addons/purchase_stock/models/purchase.py b/addons/purchase_stock/models/purchase.py
index b5e923d2b50..1a3c4987b0c 100644
--- a/addons/purchase_stock/models/purchase.py
+++ b/addons/purchase_stock/models/purchase.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 from odoo import api, fields, models, SUPERUSER_ID, _
-from odoo.tools.float_utils import float_compare
+from odoo.tools.float_utils import float_compare, float_round
 from datetime import datetime
 from dateutil.relativedelta import relativedelta
 from odoo.exceptions import UserError
@@ -382,10 +382,13 @@ class PurchaseOrderLine(models.Model):
         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:
diff --git a/addons/purchase_stock/models/stock.py b/addons/purchase_stock/models/stock.py
index 2aadedd4638..867026e986b 100644
--- a/addons/purchase_stock/models/stock.py
+++ b/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 @@ class StockMove(models.Model):
         """ 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:
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)