Fixed #21134 -- Prevented queries in broken transactions.

Squashed commit of the following:

commit 63ddb271a44df389b2c302e421fc17b7f0529755
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 29 22:51:00 2013 +0200

    Clarified interactions between atomic and exceptions.

commit 2899ec299228217c876ba3aa4024e523a41c8504
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 22 22:45:32 2013 +0200

    Fixed TransactionManagementError in tests.

    Previous commit introduced an additional check to prevent running
    queries in transactions that will be rolled back, which triggered a few
    failures in the tests. In practice using transaction.atomic instead of
    the low-level savepoint APIs was enough to fix the problems.

commit 4a639b059ea80aeb78f7f160a7d4b9f609b9c238
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Tue Sep 24 22:24:17 2013 +0200

    Allowed nesting constraint_checks_disabled inside atomic.

    Since MySQL handles transactions loosely, this isn't a problem.

commit 2a4ab1cb6e83391ff7e25d08479e230ca564bfef
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sat Sep 21 18:43:12 2013 +0200

    Prevented running queries in transactions that will be rolled back.

    This avoids a counter-intuitive behavior in an edge case on databases
    with non-atomic transaction semantics.

    It prevents using savepoint_rollback() inside an atomic block without
    calling set_rollback(False) first, which is backwards-incompatible in
    tests.

    Refs #21134.

commit 8e3db393853c7ac64a445b66e57f3620a3fde7b0
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 22 22:14:17 2013 +0200

    Replaced manual savepoints by atomic blocks.

    This ensures the rollback flag is handled consistently in internal APIs.

tests/transactions/tests.py

@@ -4,7 +4,7 @@ import sys
 from unittest import skipIf, skipUnless
 
 from django.db import connection, transaction, DatabaseError, IntegrityError
-from django.test import TransactionTestCase, skipUnlessDBFeature
+from django.test import TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.test.utils import IgnoreDeprecationWarningsMixin
 from django.utils import six
 
@@ -204,10 +204,10 @@ class AtomicTests(TransactionTestCase):
                 with transaction.atomic(savepoint=False):
                     connection.cursor().execute(
                             "SELECT no_such_col FROM transactions_reporter")
-            transaction.savepoint_rollback(sid)
-            # atomic block should rollback, but prevent it, as we just did it.
+            # prevent atomic from rolling back since we're recovering manually
             self.assertTrue(transaction.get_rollback())
             transaction.set_rollback(False)
+            transaction.savepoint_rollback(sid)
         self.assertQuerysetEqual(Reporter.objects.all(), ['<Reporter: Tintin>'])
 
 
@@ -267,11 +267,19 @@ class AtomicMergeTests(TransactionTestCase):
                     with transaction.atomic(savepoint=False):
                         Reporter.objects.create(first_name="Calculus")
                         raise Exception("Oops, that's his last name")
-                # It wasn't possible to roll back
+                # The third insert couldn't be roll back. Temporarily mark the
+                # connection as not needing rollback to check it.
+                self.assertTrue(transaction.get_rollback())
+                transaction.set_rollback(False)
                 self.assertEqual(Reporter.objects.count(), 3)
-            # It wasn't possible to roll back
+                transaction.set_rollback(True)
+            # The second insert couldn't be roll back. Temporarily mark the
+            # connection as not needing rollback to check it.
+            self.assertTrue(transaction.get_rollback())
+            transaction.set_rollback(False)
             self.assertEqual(Reporter.objects.count(), 3)
-        # The outer block must roll back
+            transaction.set_rollback(True)
+        # The first block has a savepoint and must roll back.
         self.assertQuerysetEqual(Reporter.objects.all(), [])
 
     def test_merged_inner_savepoint_rollback(self):
@@ -283,36 +291,22 @@ class AtomicMergeTests(TransactionTestCase):
                     with transaction.atomic(savepoint=False):
                         Reporter.objects.create(first_name="Calculus")
                         raise Exception("Oops, that's his last name")
-                # It wasn't possible to roll back
+                # The third insert couldn't be roll back. Temporarily mark the
+                # connection as not needing rollback to check it.
+                self.assertTrue(transaction.get_rollback())
+                transaction.set_rollback(False)
                 self.assertEqual(Reporter.objects.count(), 3)
-            # The first block with a savepoint must roll back
+                transaction.set_rollback(True)
+            # The second block has a savepoint and must roll back.
             self.assertEqual(Reporter.objects.count(), 1)
         self.assertQuerysetEqual(Reporter.objects.all(), ['<Reporter: Tintin>'])
 
-    def test_merged_outer_rollback_after_inner_failure_and_inner_success(self):
-        with transaction.atomic():
-            Reporter.objects.create(first_name="Tintin")
-            # Inner block without a savepoint fails
-            with six.assertRaisesRegex(self, Exception, "Oops"):
-                with transaction.atomic(savepoint=False):
-                    Reporter.objects.create(first_name="Haddock")
-                    raise Exception("Oops, that's his last name")
-            # It wasn't possible to roll back
-            self.assertEqual(Reporter.objects.count(), 2)
-            # Inner block with a savepoint succeeds
-            with transaction.atomic(savepoint=False):
-                Reporter.objects.create(first_name="Archibald", last_name="Haddock")
-            # It still wasn't possible to roll back
-            self.assertEqual(Reporter.objects.count(), 3)
-        # The outer block must rollback
-        self.assertQuerysetEqual(Reporter.objects.all(), [])
-
 
 @skipUnless(connection.features.uses_savepoints,
         "'atomic' requires transactions and savepoints.")
 class AtomicErrorsTests(TransactionTestCase):
 
-    available_apps = []
+    available_apps = ['transactions']
 
     def test_atomic_prevents_setting_autocommit(self):
         autocommit = transaction.get_autocommit()
@@ -336,6 +330,29 @@ class AtomicErrorsTests(TransactionTestCase):
             with self.assertRaises(transaction.TransactionManagementError):
                 transaction.leave_transaction_management()
 
+    def test_atomic_prevents_queries_in_broken_transaction(self):
+        r1 = Reporter.objects.create(first_name="Archibald", last_name="Haddock")
+        with transaction.atomic():
+            r2 = Reporter(first_name="Cuthbert", last_name="Calculus", id=r1.id)
+            with self.assertRaises(IntegrityError):
+                r2.save(force_insert=True)
+            # The transaction is marked as needing rollback.
+            with self.assertRaises(transaction.TransactionManagementError):
+                r2.save(force_update=True)
+        self.assertEqual(Reporter.objects.get(pk=r1.pk).last_name, "Haddock")
+
+    @skipIfDBFeature('atomic_transactions')
+    def test_atomic_allows_queries_after_fixing_transaction(self):
+        r1 = Reporter.objects.create(first_name="Archibald", last_name="Haddock")
+        with transaction.atomic():
+            r2 = Reporter(first_name="Cuthbert", last_name="Calculus", id=r1.id)
+            with self.assertRaises(IntegrityError):
+                r2.save(force_insert=True)
+            # Mark the transaction as no longer needing rollback.
+            transaction.set_rollback(False)
+            r2.save(force_update=True)
+        self.assertEqual(Reporter.objects.get(pk=r1.pk).last_name, "Calculus")
+
 
 class AtomicMiscTests(TransactionTestCase):