Fixed #19954 -- Fixed MySQL _last_executed decoding

Queries can contain binary data undecodable with utf-8. In this
case, using the 'replace' errors mode when decoding seems like
an acceptable representation of the query.
Thanks Marcel Ryser for the report.

django/db/backends/mysql/base.py

@@ -37,7 +37,7 @@ from django.db.backends.mysql.client import DatabaseClient
 from django.db.backends.mysql.creation import DatabaseCreation
 from django.db.backends.mysql.introspection import DatabaseIntrospection
 from django.db.backends.mysql.validation import DatabaseValidation
-from django.utils.encoding import force_str
+from django.utils.encoding import force_str, force_text
 from django.utils.safestring import SafeBytes, SafeText
 from django.utils import six
 from django.utils import timezone
@@ -270,7 +270,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         # With MySQLdb, cursor objects have an (undocumented) "_last_executed"
         # attribute where the exact query sent to the database is saved.
         # See MySQLdb/cursors.py in the source distribution.
-        return cursor._last_executed.decode('utf-8')
+        return force_text(cursor._last_executed, errors='replace')
 
     def no_limit_value(self):
         # 2**64 - 1, as recommended by the MySQL documentation

tests/backends/models.py

@@ -62,6 +62,7 @@ class Post(models.Model):
 class Reporter(models.Model):
     first_name = models.CharField(max_length=30)
     last_name = models.CharField(max_length=30)
+    raw_data = models.BinaryField()
 
     def __str__(self):
         return "%s %s" % (self.first_name, self.last_name)

tests/backends/tests.py

@@ -157,18 +157,18 @@ class DateQuotingTest(TestCase):
 class LastExecutedQueryTest(TestCase):
 
     def test_debug_sql(self):
-        list(models.Tag.objects.filter(name="test"))
+        list(models.Reporter.objects.filter(first_name="test"))
         sql = connection.queries[-1]['sql'].lower()
         self.assertIn("select", sql)
-        self.assertIn(models.Tag._meta.db_table, sql)
+        self.assertIn(models.Reporter._meta.db_table, sql)
 
     def test_query_encoding(self):
         """
         Test that last_executed_query() returns an Unicode string
         """
-        tags = models.Tag.objects.extra(select={'föö': 1})
-        sql, params = tags.query.sql_with_params()
-        cursor = tags.query.get_compiler('default').execute_sql(None)
+        persons = models.Reporter.objects.filter(raw_data=b'\x00\x46  \xFE').extra(select={'föö': 1})
+        sql, params = persons.query.sql_with_params()
+        cursor = persons.query.get_compiler('default').execute_sql(None)
         last_sql = cursor.db.ops.last_executed_query(cursor, sql, params)
         self.assertTrue(isinstance(last_sql, six.text_type))