[IMP] base: Forbid users from setting currency rate as 0 or less

   Because it doesn't have any meaning to do so. Also the default value for rate is now set to 1 instead of 0

odoo/addons/base/models/res_currency.py

@@ -222,13 +222,14 @@ class CurrencyRate(models.Model):
 
     name = fields.Date(string='Date', required=True, index=True,
                            default=lambda self: fields.Date.today())
-    rate = fields.Float(digits=(12, 6), help='The rate of the currency to the currency of rate 1')
+    rate = fields.Float(digits=(12, 6), default=1.0, help='The rate of the currency to the currency of rate 1')
     currency_id = fields.Many2one('res.currency', string='Currency', readonly=True)
     company_id = fields.Many2one('res.company', string='Company',
                                  default=lambda self: self.env.user.company_id)
 
     _sql_constraints = [
         ('unique_name_per_day', 'unique (name,currency_id,company_id)', 'Only one currency rate per day allowed!'),
+        ('currency_rate_check', 'CHECK (rate>0)', 'The currency rate must be strictly positive.'),
     ]
 
     @api.model

odoo/addons/base/tests/test_float.py

@@ -160,9 +160,12 @@ def try_roundtrip(value, expected, date):
 
         # res.currency.rate uses 6 digits of precision by default
         try_roundtrip(2.6748955, 2.674896, '2000-01-01')
-        try_roundtrip(-2.6748955, -2.674896, '2000-01-02')
         try_roundtrip(10000.999999, 10000.999999, '2000-01-03')
-        try_roundtrip(-10000.999999, -10000.999999, '2000-01-04')
+
+        #TODO re-enable those tests when tests are made on dedicated models
+        # (res.currency.rate don't accept negative value anymore)
+        #try_roundtrip(-2.6748955, -2.674896, '2000-01-02')
+        #try_roundtrip(-10000.999999, -10000.999999, '2000-01-04')
 
     def test_float_split_05(self):
         """ Test split method with 2 digits. """