From 3deafa8ebc972493c41b8264d60bb61ad90bdfc6 Mon Sep 17 00:00:00 2001
From: Raphael Collet <rco@odoo.com>
Date: Mon, 3 May 2021 16:29:26 +0000
Subject: [PATCH] [FIX] core: enable callable in api.constrains()

This avoids a call to __init__() which no longer has access to the
model's class' parent classes, and was not even correct...

closes odoo/odoo#70400

Related: odoo/enterprise#18141
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>
---
 addons/account/models/sequence_mixin.py | 5 +----
 odoo/api.py                             | 5 +++++
 odoo/models.py                          | 9 +++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/addons/account/models/sequence_mixin.py b/addons/account/models/sequence_mixin.py
index 09977376e43..60d4195d797 100644
--- a/addons/account/models/sequence_mixin.py
+++ b/addons/account/models/sequence_mixin.py
@@ -45,10 +45,7 @@ class SequenceMixin(models.AbstractModel):
                     field=sql.Identifier(self._sequence_field),
                 ))
 
-    def __init__(self, pool, cr):
-        api.constrains(self._sequence_field, self._sequence_date_field)(type(self)._constrains_date_sequence)
-        return super().__init__(pool, cr)
-
+    @api.constrains(lambda self: (self._sequence_field, self._sequence_date_field))
     def _constrains_date_sequence(self):
         # Make it possible to bypass the constraint to allow edition of already messed up documents.
         # /!\ Do not use this to completely disable the constraint as it will make this mixin unreliable.
diff --git a/odoo/api.py b/odoo/api.py
index b98a4db613b..27440797ead 100644
--- a/odoo/api.py
+++ b/odoo/api.py
@@ -127,7 +127,12 @@ def constrains(*args):
         sure a constraint will always be triggered (e.g. to test the absence of
         value).
 
+    One may also pass a single function as argument.  In that case, the field
+    names are given by calling the function with a model instance.
+
     """
+    if args and callable(args[0]):
+        args = args[0]
     return attrsetter('_constrains', args)
 
 
diff --git a/odoo/models.py b/odoo/models.py
index a07d4cccdc3..0b1861ea932 100644
--- a/odoo/models.py
+++ b/odoo/models.py
@@ -750,9 +750,18 @@ class BaseModel(metaclass=MetaModel):
         def is_constraint(func):
             return callable(func) and hasattr(func, '_constrains')
 
+        def wrap(func, names):
+            # wrap func into a proxy function with explicit '_constrains'
+            @api.constrains(*names)
+            def wrapper(self):
+                return func(self)
+            return wrapper
+
         cls = type(self)
         methods = []
         for attr, func in getmembers(cls, is_constraint):
+            if callable(func._constrains):
+                func = wrap(func, func._constrains(self))
             for name in func._constrains:
                 field = cls._fields.get(name)
                 if not field: