Support DEFAULT VALUES and VALUES(DEFAULT) individually

Fixed regression where the introduction of the INSERT syntax "INSERT...
VALUES (DEFAULT)" was not supported on some backends that do however
support "INSERT..DEFAULT VALUES", including SQLite. The two syntaxes are
now each individually supported or non-supported for each dialect, for
example MySQL supports "VALUES (DEFAULT)" but not "DEFAULT VALUES".
Support for Oracle is still not enabled as there are unresolved issues
in using RETURNING at the same time.

Fixes: #6254
Change-Id: I47959bc826e3d9d2396ccfa290eb084841b02e77

4 files changed, 31 insertions, 3 deletions

diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index 02137474b..9ff2f76eb 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -400,6 +400,7 @@ class AssertsCompiledSQL(object):
         use_default_dialect=False,
         allow_dialect_select=False,
         supports_default_values=True,
+        supports_default_metavalue=True,
         literal_binds=False,
         render_postcompile=False,
         schema_translate_map=None,
@@ -410,6 +411,7 @@ class AssertsCompiledSQL(object):
         if use_default_dialect:
             dialect = default.DefaultDialect()
             dialect.supports_default_values = supports_default_values
+            dialect.supports_default_metavalue = supports_default_metavalue
         elif allow_dialect_select:
             dialect = None
         else:
@@ -421,6 +423,7 @@ class AssertsCompiledSQL(object):
             elif dialect == "default":
                 dialect = default.DefaultDialect()
                 dialect.supports_default_values = supports_default_values
+                dialect.supports_default_metavalue = supports_default_metavalue
             elif dialect == "default_enhanced":
                 dialect = default.StrCompileDialect()
             elif isinstance(dialect, util.string_types):
diff --git a/lib/sqlalchemy/testing/assertsql.py b/lib/sqlalchemy/testing/assertsql.py
index 1bdd11585..98261a374 100644
--- a/lib/sqlalchemy/testing/assertsql.py
+++ b/lib/sqlalchemy/testing/assertsql.py
@@ -76,7 +76,11 @@ class CompiledSQL(SQLMatchRule):
 
     def _compile_dialect(self, execute_observed):
         if self.dialect == "default":
-            return DefaultDialect()
+            dialect = DefaultDialect()
+            # this is currently what tests are expecting
+            # dialect.supports_default_values = True
+            dialect.supports_default_metavalue = True
+            return dialect
         else:
             # ugh
             if self.dialect == "postgresql":
diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index f82d5f065..8a70cc692 100644
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -335,11 +335,19 @@ class SuiteRequirements(Requirements):
 
         return exclusions.only_if(
             lambda config: config.db.dialect.supports_empty_insert
-            or config.db.dialect.supports_default_values,
+            or config.db.dialect.supports_default_values
+            or config.db.dialect.supports_default_metavalue,
             "empty inserts not supported",
         )
 
     @property
+    def empty_inserts_executemany(self):
+        """target platform supports INSERT with no values, i.e.
+        INSERT DEFAULT VALUES or equivalent, within executemany()"""
+
+        return self.empty_inserts
+
+    @property
     def insert_from_select(self):
         """target platform supports INSERT from a SELECT."""
 
diff --git a/lib/sqlalchemy/testing/suite/test_insert.py b/lib/sqlalchemy/testing/suite/test_insert.py
index 35f3315c7..3c033a774 100644
--- a/lib/sqlalchemy/testing/suite/test_insert.py
+++ b/lib/sqlalchemy/testing/suite/test_insert.py
@@ -167,8 +167,21 @@ class InsertBehaviorTest(fixtures.TablesTest):
                 self.tables.autoinc_pk.c.id != None
             )
         )
+        eq_(len(r.all()), 1)
 
-        assert len(r.fetchall())
+    @requirements.empty_inserts_executemany
+    def test_empty_insert_multiple(self, connection):
+        r = connection.execute(self.tables.autoinc_pk.insert(), [{}, {}, {}])
+        assert r._soft_closed
+        assert not r.closed
+
+        r = connection.execute(
+            self.tables.autoinc_pk.select().where(
+                self.tables.autoinc_pk.c.id != None
+            )
+        )
+
+        eq_(len(r.all()), 3)
 
     @requirements.insert_from_select
     def test_insert_from_select_autoinc(self, connection):