Skip expression-based index reflection for SQLite

Reflection of an index based on SQL expressions are now skipped with a
warning, in the same way as that of the Postgresql dialect, where we currently
do not support reflecting indexes that have SQL expressions within them.
Previously, an index with columns of None were produced which would break
tools like Alembic.

Fixes: #4431
Change-Id: I1363ade912d206b42669331e2be2bb6f444b65a2

5 files changed, 58 insertions, 3 deletions

diff --git a/doc/build/changelog/unreleased_12/4431.rst b/doc/build/changelog/unreleased_12/4431.rst
new file mode 100644
index 000000000..9aea49644
--- /dev/null
+++ b/doc/build/changelog/unreleased_12/4431.rst
@@ -0,0 +1,9 @@
+.. change::
+   :tags: bug, sqlite
+   :tickets: 4431
+
+   Reflection of an index based on SQL expressions are now skipped with a
+   warning, in the same way as that of the Postgresql dialect, where we currently
+   do not support reflecting indexes that have SQL expressions within them.
+   Previously, an index with columns of None were produced which would break
+   tools like Alembic.
diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index 1eea2b6c6..424f91fa6 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -1941,17 +1941,24 @@ class SQLiteDialect(default.DefaultDialect):
                 "sqlite_autoindex"
             ):
                 continue
-
             indexes.append(dict(name=row[1], column_names=[], unique=row[2]))
 
         # loop thru unique indexes to get the column names.
-        for idx in indexes:
+        for idx in list(indexes):
             pragma_index = self._get_table_pragma(
                 connection, "index_info", idx["name"]
             )
 
             for row in pragma_index:
-                idx["column_names"].append(row[2])
+                if row[2] is None:
+                    util.warn(
+                        "Skipped unsupported reflection of "
+                        "expression-based index %s" % idx["name"]
+                    )
+                    indexes.remove(idx)
+                    break
+                else:
+                    idx["column_names"].append(row[2])
         return indexes
 
     @reflection.cache
diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index 941a9458b..ce9954cfd 100644
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -454,6 +454,11 @@ class SuiteRequirements(Requirements):
         return exclusions.open()
 
     @property
+    def indexes_with_expressions(self):
+        """target database supports CREATE INDEX against SQL expressions."""
+        return exclusions.closed()
+
+    @property
     def unique_constraint_reflection(self):
         """target dialect supports reflection of unique constraints"""
         return exclusions.open()
diff --git a/lib/sqlalchemy/testing/suite/test_reflection.py b/lib/sqlalchemy/testing/suite/test_reflection.py
index 96bd188ee..d589c046f 100644
--- a/lib/sqlalchemy/testing/suite/test_reflection.py
+++ b/lib/sqlalchemy/testing/suite/test_reflection.py
@@ -6,6 +6,7 @@ from .. import assert_raises_message
 from .. import config
 from .. import engines
 from .. import eq_
+from .. import expect_warnings
 from .. import fixtures
 from .. import is_
 from ..schema import Column
@@ -792,6 +793,35 @@ class ComponentReflectionTest(fixtures.TablesTest):
     def test_get_noncol_index_pk(self):
         self._test_get_noncol_index("noncol_idx_test_pk", "noncol_idx_pk")
 
+    @testing.requires.indexes_with_expressions
+    @testing.provide_metadata
+    def test_reflect_expression_based_indexes(self):
+        Table(
+            "t",
+            self.metadata,
+            Column("x", String(30)),
+            Column("y", String(30)),
+        )
+        event.listen(
+            self.metadata,
+            "after_create",
+            DDL("CREATE INDEX t_idx ON t(lower(x), lower(y))"),
+        )
+        event.listen(
+            self.metadata, "after_create", DDL("CREATE INDEX t_idx_2 ON t(x)")
+        )
+        self.metadata.create_all()
+
+        insp = inspect(self.metadata.bind)
+
+        with expect_warnings(
+            "Skipped unsupported reflection of expression-based index t_idx"
+        ):
+            eq_(
+                insp.get_indexes("t"),
+                [{"name": "t_idx_2", "column_names": ["x"], "unique": 0}],
+            )
+
     @testing.requires.unique_constraint_reflection
     def test_get_unique_constraints(self):
         self._test_get_unique_constraints()
diff --git a/test/requirements.py b/test/requirements.py
index d95a3c58b..c70169acf 100644
--- a/test/requirements.py
+++ b/test/requirements.py
@@ -457,6 +457,10 @@ class DefaultRequirements(SuiteRequirements):
         )
 
     @property
+    def indexes_with_expressions(self):
+        return only_on(["postgresql", "sqlite>=3.9.0"])
+
+    @property
     def temp_table_names(self):
         """target dialect supports listing of temporary table names"""