- repair a regression caused by #3282, where we no longer were

applying any topological sort to tables on SQLite.  See the
changelog for details, but we now continue to sort
tables for SQLite on DROP, prohibit the sort from considering
alter, and only warn if we encounter an unresolvable cycle, in
which case, then we forego the ordering.  use_alter as always
is used to break such a cycle.
fixes #3378

4 files changed, 50 insertions, 18 deletions

diff --git a/lib/sqlalchemy/sql/ddl.py b/lib/sqlalchemy/sql/ddl.py
index bbac6456e..a0841b13c 100644
--- a/lib/sqlalchemy/sql/ddl.py
+++ b/lib/sqlalchemy/sql/ddl.py
@@ -803,32 +803,50 @@ class SchemaDropper(DDLBase):
             tables = list(metadata.tables.values())
 
         try:
+            unsorted_tables = [t for t in tables if self._can_drop_table(t)]
             collection = reversed(
                 sort_tables_and_constraints(
-                    [t for t in tables if self._can_drop_table(t)],
-                    filter_fn=
-                    lambda constraint: True if not self.dialect.supports_alter
-                    else False if constraint.name is None
+                    unsorted_tables,
+                    filter_fn=lambda constraint: False
+                    if not self.dialect.supports_alter
+                    or constraint.name is None
                     else None
                 )
             )
         except exc.CircularDependencyError as err2:
-            util.raise_from_cause(
-                exc.CircularDependencyError(
-                    err2.args[0],
-                    err2.cycles, err2.edges,
-                    msg="Can't sort tables for DROP; an "
+            if not self.dialect.supports_alter:
+                util.warn(
+                    "Can't sort tables for DROP; an "
                     "unresolvable foreign key "
-                    "dependency exists between tables: %s.  Please ensure "
-                    "that the ForeignKey and ForeignKeyConstraint objects "
-                    "involved in the cycle have "
-                    "names so that they can be dropped using DROP CONSTRAINT."
+                    "dependency exists between tables: %s, and backend does "
+                    "not support ALTER.  To restore at least a partial sort, "
+                    "apply use_alter=True to ForeignKey and "
+                    "ForeignKeyConstraint "
+                    "objects involved in the cycle to mark these as known "
+                    "cycles that will be ignored."
                     % (
                         ", ".join(sorted([t.fullname for t in err2.cycles]))
                     )
+                )
+                collection = [(t, ()) for t in unsorted_tables]
+            else:
+                util.raise_from_cause(
+                    exc.CircularDependencyError(
+                        err2.args[0],
+                        err2.cycles, err2.edges,
+                        msg="Can't sort tables for DROP; an "
+                        "unresolvable foreign key "
+                        "dependency exists between tables: %s.  Please ensure "
+                        "that the ForeignKey and ForeignKeyConstraint objects "
+                        "involved in the cycle have "
+                        "names so that they can be dropped using "
+                        "DROP CONSTRAINT."
+                        % (
+                            ", ".join(sorted([t.fullname for t in err2.cycles]))
+                        )
 
+                    )
                 )
-            )
 
         seq_coll = [
             s
diff --git a/lib/sqlalchemy/testing/assertsql.py b/lib/sqlalchemy/testing/assertsql.py
index e544adad2..243493607 100644
--- a/lib/sqlalchemy/testing/assertsql.py
+++ b/lib/sqlalchemy/testing/assertsql.py
@@ -188,21 +188,27 @@ class DialectSQL(CompiledSQL):
     def _compile_dialect(self, execute_observed):
         return execute_observed.context.dialect
 
+    def _compare_no_space(self, real_stmt, received_stmt):
+        stmt = re.sub(r'[\n\t]', '', real_stmt)
+        return received_stmt == stmt
+
     def _received_statement(self, execute_observed):
         received_stmt, received_params = super(DialectSQL, self).\
             _received_statement(execute_observed)
+
+        # TODO: why do we need this part?
         for real_stmt in execute_observed.statements:
-            if real_stmt.statement == received_stmt:
+            if self._compare_no_space(real_stmt.statement, received_stmt):
                 break
         else:
             raise AssertionError(
                 "Can't locate compiled statement %r in list of "
                 "statements actually invoked" % received_stmt)
+
         return received_stmt, execute_observed.context.compiled_parameters
 
     def _compare_sql(self, execute_observed, received_statement):
         stmt = re.sub(r'[\n\t]', '', self.statement)
-
         # convert our comparison statement to have the
         # paramstyle of the received
         paramstyle = execute_observed.context.dialect.paramstyle
diff --git a/lib/sqlalchemy/testing/engines.py b/lib/sqlalchemy/testing/engines.py
index 3a8303546..8bd1becbf 100644
--- a/lib/sqlalchemy/testing/engines.py
+++ b/lib/sqlalchemy/testing/engines.py
@@ -98,7 +98,14 @@ def drop_all_tables(metadata, bind):
     testing_reaper.close_all()
     if hasattr(bind, 'close'):
         bind.close()
-    metadata.drop_all(bind)
+
+    if not config.db.dialect.supports_alter:
+        from . import assertions
+        with assertions.expect_warnings(
+                "Can't sort tables", assert_=False):
+            metadata.drop_all(bind)
+    else:
+        metadata.drop_all(bind)
 
 
 @decorator
diff --git a/lib/sqlalchemy/testing/util.py b/lib/sqlalchemy/testing/util.py
index 6d6fa094e..1842e58a5 100644
--- a/lib/sqlalchemy/testing/util.py
+++ b/lib/sqlalchemy/testing/util.py
@@ -185,6 +185,7 @@ def provide_metadata(fn, *args, **kw):
     """Provide bound MetaData for a single test, dropping afterwards."""
 
     from . import config
+    from . import engines
     from sqlalchemy import schema
 
     metadata = schema.MetaData(config.db)
@@ -194,7 +195,7 @@ def provide_metadata(fn, *args, **kw):
     try:
         return fn(*args, **kw)
     finally:
-        metadata.drop_all()
+        engines.drop_all_tables(metadata, config.db)
         self.metadata = prev_meta