Ensure all nested exception throws have a cause

Applied an explicit "cause" to most if not all internally raised exceptions
that are raised from within an internal exception catch, to avoid
misleading stacktraces that suggest an error within the handling of an
exception.  While it would be preferable to suppress the internally caught
exception in the way that the ``__suppress_context__`` attribute would,
there does not as yet seem to be a way to do this without suppressing an
enclosing user constructed context, so for now it exposes the internally
caught exception as the cause so that full information about the context
of the error is maintained.

Fixes: #4849
Change-Id: I55a86b29023675d9e5e49bc7edc5a2dc0bcd4751

4 files changed, 16 insertions, 15 deletions

diff --git a/test/engine/test_execute.py b/test/engine/test_execute.py
index 5acd14177..cf262a573 100644
--- a/test/engine/test_execute.py
+++ b/test/engine/test_execute.py
@@ -712,12 +712,13 @@ class ExecuteTest(fixtures.TestBase):
                     return super(MockCursor, self).execute(stmt, params, **kw)
 
         eng = engines.proxying_engine(cursor_cls=MockCursor)
-        assert_raises_message(
-            tsa.exc.SAWarning,
-            "Exception attempting to detect unicode returns",
-            eng.connect,
-        )
-        assert eng.dialect.returns_unicode_strings in (True, False)
+        with testing.expect_warnings(
+            "Exception attempting to detect unicode returns"
+        ):
+            eng.connect()
+
+        # because plain varchar passed, we don't know the correct answer
+        eq_(eng.dialect.returns_unicode_strings, "conditional")
         eng.dispose()
 
     def test_works_after_dispose(self):
diff --git a/test/engine/test_pool.py b/test/engine/test_pool.py
index cfe20f5ec..72e0fa186 100644
--- a/test/engine/test_pool.py
+++ b/test/engine/test_pool.py
@@ -10,6 +10,7 @@ from sqlalchemy import pool
 from sqlalchemy import select
 from sqlalchemy import testing
 from sqlalchemy.testing import assert_raises
+from sqlalchemy.testing import assert_raises_context_ok
 from sqlalchemy.testing import assert_raises_message
 from sqlalchemy.testing import eq_
 from sqlalchemy.testing import fixtures
@@ -1256,7 +1257,7 @@ class QueuePoolTest(PoolTestBase):
             eq_(p.checkedout(), 0)
             eq_(p._overflow, 0)
             dbapi.shutdown(True)
-            assert_raises(Exception, p.connect)
+            assert_raises_context_ok(Exception, p.connect)
             eq_(p._overflow, 0)
             eq_(p.checkedout(), 0)  # and not 1
 
diff --git a/test/engine/test_reconnect.py b/test/engine/test_reconnect.py
index 205c1fb31..000be1a70 100644
--- a/test/engine/test_reconnect.py
+++ b/test/engine/test_reconnect.py
@@ -14,6 +14,7 @@ from sqlalchemy import util
 from sqlalchemy.engine import url
 from sqlalchemy.testing import assert_raises
 from sqlalchemy.testing import assert_raises_message
+from sqlalchemy.testing import assert_raises_message_context_ok
 from sqlalchemy.testing import engines
 from sqlalchemy.testing import eq_
 from sqlalchemy.testing import expect_warnings
@@ -255,7 +256,7 @@ class PrePingMockTest(fixtures.TestBase):
 
         self.dbapi.shutdown("execute", stop=True)
 
-        assert_raises_message(
+        assert_raises_message_context_ok(
             MockDisconnect, "database is stopped", pool.connect
         )
 
@@ -835,7 +836,7 @@ class CursorErrTest(fixtures.TestBase):
 
     def test_cursor_shutdown_in_initialize(self):
         db = self._fixture(True, True)
-        assert_raises_message(
+        assert_raises_message_context_ok(
             exc.SAWarning, "Exception attempting to detect", db.connect
         )
         eq_(
diff --git a/test/engine/test_reflection.py b/test/engine/test_reflection.py
index 301614061..579f1aece 100644
--- a/test/engine/test_reflection.py
+++ b/test/engine/test_reflection.py
@@ -24,6 +24,7 @@ from sqlalchemy.testing import eq_regex
 from sqlalchemy.testing import expect_warnings
 from sqlalchemy.testing import fixtures
 from sqlalchemy.testing import in_
+from sqlalchemy.testing import is_
 from sqlalchemy.testing import is_false
 from sqlalchemy.testing import is_true
 from sqlalchemy.testing import mock
@@ -596,13 +597,10 @@ class ReflectionTest(fixtures.TestBase, ComparesTables):
         testing.db.dialect.ischema_names = {}
         try:
             m2 = MetaData(testing.db)
-            assert_raises(sa.exc.SAWarning, Table, "test", m2, autoload=True)
 
-            @testing.emits_warning("Did not recognize type")
-            def warns():
-                m3 = MetaData(testing.db)
-                t3 = Table("test", m3, autoload=True)
-                assert t3.c.foo.type.__class__ == sa.types.NullType
+            with testing.expect_warnings("Did not recognize type"):
+                t3 = Table("test", m2, autoload_with=testing.db)
+                is_(t3.c.foo.type.__class__, sa.types.NullType)
 
         finally:
             testing.db.dialect.ischema_names = ischema_names