Explicitly test for Connection in dialect.has_table()

The :meth:`_engine.Dialect.has_table` method now raises an informative
exception if a non-Connection is passed to it, as this incorrect behavior
seems to be common.  This method is not intended for external use outside
of a dialect.  Please use the :meth:`.Inspector.has_table` method
or for cross-compatibility with older SQLAlchemy versions, the
:meth:`_engine.Engine.has_table` method.

Fixes: #5780
Fixes: #6062
Fixes: #6260
Change-Id: I9b2439675167019b68d682edee3dcdcfce836987

1 files changed, 14 insertions, 0 deletions

diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index d45b6d7a7..375a93a48 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -22,6 +22,7 @@ import weakref
 from . import characteristics
 from . import cursor as _cursor
 from . import interfaces
+from .base import Connection
 from .. import event
 from .. import exc
 from .. import pool
@@ -323,6 +324,19 @@ class DefaultDialect(interfaces.Dialect):
         self._encoder = codecs.getencoder(self.encoding)
         self._decoder = processors.to_unicode_processor_factory(self.encoding)
 
+    def _ensure_has_table_connection(self, arg):
+
+        if not isinstance(arg, Connection):
+            raise exc.ArgumentError(
+                "The argument passed to Dialect.has_table() should be a "
+                "%s, got %s. "
+                "Additionally, the Dialect.has_table() method is for "
+                "internal dialect "
+                "use only; please use "
+                "``inspect(some_engine).has_table(<tablename>>)`` "
+                "for public API use." % (Connection, type(arg))
+            )
+
     @util.memoized_property
     def _supports_statement_cache(self):
         return (