[FIX] mail_environment: add search field for fetchmail.server's is_ssl

Fixes

```
while parsing /home/odoo/16.0/addons/mail/views/fetchmail_views.xml:88
Error while validating view near:

                    <separator/>
                    <filter string="SSL" name="ssl" domain="[('is_ssl', '=', True)]" help="If SSL required."/>
                    <separator/>
                    <filter string="Archived" name="inactive" domain="[('active', '=', False)]"/>
                </search>
Unsearchable field 'is_ssl' in path 'is_ssl' in domain of <filter name="ssl"> ([('is_ssl', '=', True)]))
```

While upgrading --all on a setup with mail_environment installed.

mail_environment/models/fetchmail_server.py

@@ -4,6 +4,7 @@
 import operator
 
 from odoo import api, fields, models
+from odoo.osv.expression import FALSE_DOMAIN
 
 
 class FetchmailServer(models.Model):
@@ -28,6 +29,7 @@ class FetchmailServer(models.Model):
         mail_fields.update(base_fields)
         return mail_fields
 
+    is_ssl = fields.Boolean(search="_search_is_ssl")
     server_type = fields.Selection(search="_search_server_type")
 
     @api.model
@@ -38,6 +40,20 @@ class FetchmailServer(models.Model):
         """
         return "incoming_mail"
 
+    @api.model
+    def _search_is_ssl(self, oper, value):
+        """Keep the is_ssl field searchable to allow domain in search view."""
+        if not isinstance(value, bool):
+            return FALSE_DOMAIN
+        operators = {
+            "=": operator.eq,
+            "!=": operator.ne,
+        }
+        if oper not in operators:
+            return FALSE_DOMAIN
+        servers = self.search([]).filtered(lambda s: operators[oper](value, s.is_ssl))
+        return [("id", "in", servers.ids)]
+
     @api.model
     def _search_server_type(self, oper, value):
         operators = {

mail_environment/tests/__init__.py

@@ -0,0 +1 @@
+from . import test_mail_environment

mail_environment/tests/test_mail_environment.py

@@ -0,0 +1,77 @@
+# Copyright 2018 Camptocamp (https://www.camptocamp.com).
+# License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl.html)
+
+
+from odoo.addons.server_environment.tests.common import ServerEnvironmentCase
+
+fetchmail_config = """
+[incoming_mail.fetchmail1]
+server = safe_server
+port = 993
+server_type = imap
+is_ssl = 1
+attach = 1
+original = 1
+user = admin
+password = admin
+state = done
+priority = 1
+active = 1
+
+[incoming_mail.fetchmail2]
+server = unsafe_server
+port = 143
+server_type = imap
+is_ssl = 0
+attach = 1
+original = 1
+user = admin
+password = admin
+state = done
+priority = 1
+active = 1
+"""
+
+
+class TestMailEnvironment(ServerEnvironmentCase):
+    def test_fetchmail_search_is_ssl(self):
+        fetchmail1 = self.env["fetchmail.server"].create({"name": "fetchmail1"})
+        fetchmail2 = self.env["fetchmail.server"].create({"name": "fetchmail2"})
+        with self.load_config(public=fetchmail_config):
+            # Test basic properties
+            self.assertTrue(fetchmail1.is_ssl)
+            self.assertEqual(fetchmail1.port, 993)
+            self.assertFalse(fetchmail2.is_ssl)
+            self.assertEqual(fetchmail2.port, 143)
+
+            # Test is_ssl search method
+            self.assertIn(
+                fetchmail1, self.env["fetchmail.server"].search([("is_ssl", "=", True)])
+            )
+            self.assertIn(
+                fetchmail1,
+                self.env["fetchmail.server"].search([("is_ssl", "!=", False)]),
+            )
+            self.assertNotIn(
+                fetchmail1,
+                self.env["fetchmail.server"].search([("is_ssl", "=", False)]),
+            )
+            self.assertNotIn(
+                fetchmail1,
+                self.env["fetchmail.server"].search([("is_ssl", "!=", True)]),
+            )
+            self.assertNotIn(
+                fetchmail2, self.env["fetchmail.server"].search([("is_ssl", "=", True)])
+            )
+            self.assertNotIn(
+                fetchmail2,
+                self.env["fetchmail.server"].search([("is_ssl", "!=", False)]),
+            )
+            self.assertIn(
+                fetchmail2,
+                self.env["fetchmail.server"].search([("is_ssl", "=", False)]),
+            )
+            self.assertIn(
+                fetchmail2,
+                self.env["fetchmail.server"].search([("is_ssl", "!=", True)]),
+            )