dont compare unique constraint and index sigs to each other

Fixed regression caused by :ticket:`1166` released in version 1.10.0 which
caused MySQL unique constraints with multiple columns to not compare
correctly within autogenerate, due to different sorting rules on unique
constraints vs. indexes, which in MySQL are shared constructs.

Change-Id: I5687dde95281f237fd73367d145b9c62e2576a3a
Fixes: #1240

3 files changed, 89 insertions, 5 deletions

diff --git a/alembic/autogenerate/compare.py b/alembic/autogenerate/compare.py
index b489328..5727891 100644
--- a/alembic/autogenerate/compare.py
+++ b/alembic/autogenerate/compare.py
@@ -452,7 +452,9 @@ class _uq_constraint_sig(_constraint_sig):
     def __init__(self, const: UniqueConstraint) -> None:
         self.const = const
         self.name = const.name
-        self.sig = tuple(sorted([col.name for col in const.columns]))
+        self.sig = ("UNIQUE_CONSTRAINT",) + tuple(
+            sorted([col.name for col in const.columns])
+        )
 
     @property
     def column_names(self) -> List[str]:
@@ -465,7 +467,7 @@ class _ix_constraint_sig(_constraint_sig):
     def __init__(self, const: Index, impl: DefaultImpl) -> None:
         self.const = const
         self.name = const.name
-        self.sig = impl.create_index_sig(const)
+        self.sig = ("INDEX",) + impl.create_index_sig(const)
         self.is_unique = bool(const.unique)
 
     def md_name_to_sql_name(self, context: AutogenContext) -> Optional[str]:
@@ -807,11 +809,11 @@ def _compare_indexes_and_uniques(
         if not conn_obj.is_index and conn_obj.sig in unnamed_metadata_uniques:
             continue
         elif removed_name in doubled_constraints:
+            conn_uq, conn_idx = doubled_constraints[removed_name]
             if (
-                conn_obj.sig not in metadata_indexes_by_sig
-                and conn_obj.sig not in metadata_uniques_by_sig
+                conn_idx.sig not in metadata_indexes_by_sig
+                and conn_uq.sig not in metadata_uniques_by_sig
             ):
-                conn_uq, conn_idx = doubled_constraints[removed_name]
                 obj_removed(conn_uq)
                 obj_removed(conn_idx)
         else:
diff --git a/docs/build/unreleased/1240.rst b/docs/build/unreleased/1240.rst
new file mode 100644
index 0000000..19cfd81
--- /dev/null
+++ b/docs/build/unreleased/1240.rst
@@ -0,0 +1,8 @@
+.. change::
+    :tags: bug, mysql, regression
+    :tickets: 1240
+
+    Fixed regression caused by :ticket:`1166` released in version 1.10.0 which
+    caused MySQL unique constraints with multiple columns to not compare
+    correctly within autogenerate, due to different sorting rules on unique
+    constraints vs. indexes, which in MySQL are shared constructs.
diff --git a/tests/test_autogen_indexes.py b/tests/test_autogen_indexes.py
index f697e5a..abefd66 100644
--- a/tests/test_autogen_indexes.py
+++ b/tests/test_autogen_indexes.py
@@ -463,6 +463,80 @@ class AutogenerateUniqueIndexTest(AutogenFixtureTest, TestBase):
         eq_(diffs, [])
 
     @config.requirements.unique_constraint_reflection
+    def test_nothing_changed_cols_unsorted(self):
+        """test #1240
+
+
+        MySQL doubles unique constraints as indexes, so we need to make
+        sure we aren't comparing index sigs to unique constraint sigs,
+        which we were doing previously by mistake.  As their signatures
+        were compatible, things "worked" but once index sigs changed
+        col name sorting order, it broke.
+
+        """
+
+        m1 = MetaData()
+        m2 = MetaData()
+
+        Table(
+            "nothing_changed",
+            m1,
+            Column("id", Integer, primary_key=True),
+            Column("sid", Integer, nullable=False),
+            Column("label", String(30), nullable=False),
+            Column("fid", Integer, nullable=False),
+            UniqueConstraint("sid", "label"),
+            UniqueConstraint("sid", "fid"),
+        )
+
+        Table(
+            "nothing_changed",
+            m2,
+            Column("id", Integer, primary_key=True),
+            Column("sid", Integer, nullable=False),
+            Column("label", String(30), nullable=False),
+            Column("fid", Integer, nullable=False),
+            UniqueConstraint("sid", "label"),
+            UniqueConstraint("sid", "fid"),
+        )
+
+        diffs = self._fixture(m1, m2)
+        eq_(diffs, [])
+
+    @config.requirements.unique_constraint_reflection
+    @config.requirements.reports_unnamed_constraints
+    def test_remove_uq_constraint(self):
+        """supplementary test for codepath in #1240"""
+
+        m1 = MetaData()
+        m2 = MetaData()
+
+        Table(
+            "something_changed",
+            m1,
+            Column("id", Integer, primary_key=True),
+            Column("sid", Integer, nullable=False),
+            Column("label", String(30), nullable=False),
+            Column("fid", Integer, nullable=False),
+            UniqueConstraint("sid", "label"),
+            UniqueConstraint("sid", "fid"),
+        )
+
+        Table(
+            "something_changed",
+            m2,
+            Column("id", Integer, primary_key=True),
+            Column("sid", Integer, nullable=False),
+            Column("label", String(30), nullable=False),
+            Column("fid", Integer, nullable=False),
+            UniqueConstraint("sid", "fid"),
+        )
+
+        diffs = self._fixture(m1, m2)
+        assert len(diffs) == 1
+        assert diffs[0][0] in ("remove_index", "remove_constraint")
+
+    @config.requirements.unique_constraint_reflection
     def test_uq_casing_convention_changed_so_put_drops_first(self):
         m1 = MetaData()
         m2 = MetaData()