Improved support for expression indexes

Added support for autogenerate comparison of indexes on PostgreSQL which
include SQL expressions; the previous warning that such indexes were
skipped is now removed. This functionality requires SQLAlchemy 2.0.
For older SQLAlchemy versions, these indexes are still skipped.

Fixed issue where indexes on SQLite which include SQL expressions would not
compare against themselves correctly, generating false positives.
SQLAlchemy as of version 2 has no support for reflecting expression based
indexes on SQLite; so for now, the behavior is that SQLite expression-based
indexes are ignored for autogenerate compare, in the same way that
PostgreSQL expression-based indexes were ignored for the time that
SQLAlchemy did not support reflection of such indexes (which is now
supported in SQLAlchemy 2.0 as well as this release of Alembic).

Fixed issue in index detection where autogenerate change detection would
consider indexes with the same columns but with different order as equal,
while in general they are not equivalent in how a database will use them.

Fixes: #1165
Fixes: #1166
Change-Id: I226408eed855b923172e5df0bdab005ed2cc9f53

9 files changed, 120 insertions, 41 deletions

diff --git a/alembic/autogenerate/compare.py b/alembic/autogenerate/compare.py
index 828a4cd..d97eb9c 100644
--- a/alembic/autogenerate/compare.py
+++ b/alembic/autogenerate/compare.py
@@ -17,6 +17,7 @@ from typing import Union
 from sqlalchemy import event
 from sqlalchemy import inspect
 from sqlalchemy import schema as sa_schema
+from sqlalchemy import text
 from sqlalchemy import types as sqltypes
 from sqlalchemy.util import OrderedSet
 
@@ -30,6 +31,7 @@ if TYPE_CHECKING:
 
     from sqlalchemy.engine.reflection import Inspector
     from sqlalchemy.sql.elements import quoted_name
+    from sqlalchemy.sql.elements import TextClause
     from sqlalchemy.sql.schema import Column
     from sqlalchemy.sql.schema import ForeignKeyConstraint
     from sqlalchemy.sql.schema import Index
@@ -37,6 +39,7 @@ if TYPE_CHECKING:
     from sqlalchemy.sql.schema import UniqueConstraint
 
     from alembic.autogenerate.api import AutogenContext
+    from alembic.ddl.impl import DefaultImpl
     from alembic.operations.ops import AlterColumnOp
     from alembic.operations.ops import MigrationScript
     from alembic.operations.ops import ModifyTableOps
@@ -276,14 +279,12 @@ def _compare_tables(
 
 
 def _make_index(params: Dict[str, Any], conn_table: Table) -> Optional[Index]:
-    exprs = []
-    for col_name in params["column_names"]:
+    exprs: list[Union[Column[Any], TextClause]] = []
+    for num, col_name in enumerate(params["column_names"]):
+        item: Union[Column[Any], TextClause]
         if col_name is None:
-            util.warn(
-                "Skipping reflected expression-based "
-                f"index {params['name']!r}"
-            )
-            return None
+            assert "expressions" in params
+            item = text(params["expressions"][num])
         else:
             item = conn_table.c[col_name]
         exprs.append(item)
@@ -439,10 +440,10 @@ class _uq_constraint_sig(_constraint_sig):
 class _ix_constraint_sig(_constraint_sig):
     is_index = True
 
-    def __init__(self, const: Index) -> None:
+    def __init__(self, const: Index, impl: DefaultImpl) -> None:
         self.const = const
         self.name = const.name
-        self.sig = tuple(sorted([col.name for col in const.columns]))
+        self.sig = impl.create_index_sig(const)
         self.is_unique = bool(const.unique)
 
     def md_name_to_sql_name(self, context: AutogenContext) -> Optional[str]:
@@ -624,11 +625,14 @@ def _compare_indexes_and_uniques(
         _uq_constraint_sig(uq) for uq in metadata_unique_constraints
     }
 
-    metadata_indexes_sig = {_ix_constraint_sig(ix) for ix in metadata_indexes}
+    impl = autogen_context.migration_context.impl
+    metadata_indexes_sig = {
+        _ix_constraint_sig(ix, impl) for ix in metadata_indexes
+    }
 
     conn_unique_constraints = {_uq_constraint_sig(uq) for uq in conn_uniques}
 
-    conn_indexes_sig = {_ix_constraint_sig(ix) for ix in conn_indexes}
+    conn_indexes_sig = {_ix_constraint_sig(ix, impl) for ix in conn_indexes}
 
     # 5. index things by name, for those objects that have names
     metadata_names = {
@@ -816,7 +820,7 @@ def _compare_indexes_and_uniques(
                 )
             if conn_obj.sig != metadata_obj.sig:
                 msg.append(
-                    " columns %r to %r" % (conn_obj.sig, metadata_obj.sig)
+                    " expression %r to %r" % (conn_obj.sig, metadata_obj.sig)
                 )
 
             if msg:
diff --git a/alembic/ddl/impl.py b/alembic/ddl/impl.py
index 728d1da..f11d1ed 100644
--- a/alembic/ddl/impl.py
+++ b/alembic/ddl/impl.py
@@ -665,6 +665,27 @@ class DefaultImpl(metaclass=ImplMeta):
             bool(diff) or bool(metadata_identity) != bool(inspector_identity),
         )
 
+    def create_index_sig(self, index: Index) -> Tuple[Any, ...]:
+        # order of col matters in an index
+        return tuple(col.name for col in index.columns)
+
+    def _skip_functional_indexes(self, metadata_indexes, conn_indexes):
+        conn_indexes_by_name = {c.name: c for c in conn_indexes}
+
+        for idx in list(metadata_indexes):
+            if idx.name in conn_indexes_by_name:
+                continue
+            iex = sqla_compat.is_expression_index(idx)
+            if iex:
+                util.warn(
+                    "autogenerate skipping metadata-specified "
+                    "expression-based index "
+                    f"{idx.name!r}; dialect {self.__dialect__!r} under "
+                    f"SQLAlchemy {sqla_compat.sqlalchemy_version} can't "
+                    "reflect these indexes so they can't be compared"
+                )
+                metadata_indexes.discard(idx)
+
 
 def _compare_identity_options(
     attributes, metadata_io, inspector_io, default_io
diff --git a/alembic/ddl/postgresql.py b/alembic/ddl/postgresql.py
index 32674d2..e7b0a48 100644
--- a/alembic/ddl/postgresql.py
+++ b/alembic/ddl/postgresql.py
@@ -12,6 +12,7 @@ from typing import TYPE_CHECKING
 from typing import Union
 
 from sqlalchemy import Column
+from sqlalchemy import Index
 from sqlalchemy import literal_column
 from sqlalchemy import Numeric
 from sqlalchemy import text
@@ -21,7 +22,6 @@ from sqlalchemy.dialects.postgresql import ExcludeConstraint
 from sqlalchemy.dialects.postgresql import INTEGER
 from sqlalchemy.schema import CreateIndex
 from sqlalchemy.sql.elements import ColumnClause
-from sqlalchemy.sql.elements import UnaryExpression
 from sqlalchemy.types import NULLTYPE
 
 from .base import alter_column
@@ -235,8 +235,6 @@ class PostgresqlImpl(DefaultImpl):
         metadata_indexes,
     ):
 
-        conn_indexes_by_name = {c.name: c for c in conn_indexes}
-
         doubled_constraints = {
             index
             for index in conn_indexes
@@ -246,23 +244,41 @@ class PostgresqlImpl(DefaultImpl):
         for ix in doubled_constraints:
             conn_indexes.remove(ix)
 
-        for idx in list(metadata_indexes):
-            if idx.name in conn_indexes_by_name:
-                continue
-            exprs = idx.expressions
-            for expr in exprs:
-                while isinstance(expr, UnaryExpression):
-                    expr = expr.element
-                if not isinstance(expr, Column):
-                    if sqla_compat.sqla_2:
-                        msg = ""
-                    else:
-                        msg = "; not supported by SQLAlchemy reflection"
-                    util.warn(
-                        "autogenerate skipping functional index "
-                        f"{idx.name!r}{msg}"
-                    )
-                    metadata_indexes.discard(idx)
+        if not sqla_compat.sqla_2:
+            self._skip_functional_indexes(metadata_indexes, conn_indexes)
+
+    def _cleanup_index_expr(self, index: Index, expr: str) -> str:
+        # start = expr
+        expr = expr.lower()
+        expr = expr.replace('"', "")
+        if index.table is not None:
+            expr = expr.replace(f"{index.table.name.lower()}.", "")
+
+        while expr and expr[0] == "(" and expr[-1] == ")":
+            expr = expr[1:-1]
+        if "::" in expr:
+            # strip :: cast. types can have spaces in them
+            expr = re.sub(r"(::[\w ]+\w)", "", expr)
+
+        # print(f"START: {start} END: {expr}")
+        return expr
+
+    def create_index_sig(self, index: Index) -> Tuple[Any, ...]:
+        if sqla_compat.is_expression_index(index):
+            return tuple(
+                self._cleanup_index_expr(
+                    index,
+                    e
+                    if isinstance(e, str)
+                    else e.compile(
+                        dialect=self.dialect,
+                        compile_kwargs={"literal_binds": True},
+                    ).string,
+                )
+                for e in index.expressions
+            )
+        else:
+            return super().create_index_sig(index)
 
     def render_type(
         self, type_: TypeEngine, autogen_context: AutogenContext
diff --git a/alembic/ddl/sqlite.py b/alembic/ddl/sqlite.py
index 6b8c293..302a877 100644
--- a/alembic/ddl/sqlite.py
+++ b/alembic/ddl/sqlite.py
@@ -186,6 +186,16 @@ class SQLiteImpl(DefaultImpl):
                 existing_transfer["expr"], new_type
             )
 
+    def correct_for_autogen_constraints(
+        self,
+        conn_unique_constraints,
+        conn_indexes,
+        metadata_unique_constraints,
+        metadata_indexes,
+    ):
+
+        self._skip_functional_indexes(metadata_indexes, conn_indexes)
+
 
 @compiles(RenameTable, "sqlite")
 def visit_rename_table(
diff --git a/alembic/testing/requirements.py b/alembic/testing/requirements.py
index 6896276..989c7cd 100644
--- a/alembic/testing/requirements.py
+++ b/alembic/testing/requirements.py
@@ -96,6 +96,13 @@ class SuiteRequirements(Requirements):
         )
 
     @property
+    def sqlalchemy_2(self):
+        return exclusions.skip_if(
+            lambda config: not util.sqla_2,
+            "SQLAlchemy 2.x test",
+        )
+
+    @property
     def comments(self):
         return exclusions.only_if(
             lambda config: config.db.dialect.supports_comments
diff --git a/alembic/testing/schemacompare.py b/alembic/testing/schemacompare.py
index 4409421..c063499 100644
--- a/alembic/testing/schemacompare.py
+++ b/alembic/testing/schemacompare.py
@@ -43,15 +43,19 @@ class CompareColumn:
 
 
 class CompareIndex:
-    def __init__(self, index):
+    def __init__(self, index, name_only=False):
         self.index = index
+        self.name_only = name_only
 
     def __eq__(self, other):
-        return (
-            str(schema.CreateIndex(self.index))
-            == str(schema.CreateIndex(other))
-            and self.index.dialect_kwargs == other.dialect_kwargs
-        )
+        if self.name_only:
+            return self.index.name == other.name
+        else:
+            return (
+                str(schema.CreateIndex(self.index))
+                == str(schema.CreateIndex(other))
+                and self.index.dialect_kwargs == other.dialect_kwargs
+            )
 
     def __ne__(self, other):
         return not self.__eq__(other)
diff --git a/alembic/testing/util.py b/alembic/testing/util.py
index a82690d..e65597d 100644
--- a/alembic/testing/util.py
+++ b/alembic/testing/util.py
@@ -10,6 +10,8 @@ import re
 import types
 from typing import Union
 
+from sqlalchemy.util import inspect_getfullargspec
+
 
 def flag_combinations(*combinations):
     """A facade around @testing.combinations() oriented towards boolean
@@ -69,10 +71,12 @@ def resolve_lambda(__fn, **kw):
 
     """
 
+    pos_args = inspect_getfullargspec(__fn)[0]
+    pass_pos_args = {arg: kw.pop(arg) for arg in pos_args}
     glb = dict(__fn.__globals__)
     glb.update(kw)
     new_fn = types.FunctionType(__fn.__code__, glb)
-    return new_fn()
+    return new_fn(**pass_pos_args)
 
 
 def metadata_fixture(ddl="function"):
diff --git a/alembic/util/__init__.py b/alembic/util/__init__.py
index 4374f46..c81d431 100644
--- a/alembic/util/__init__.py
+++ b/alembic/util/__init__.py
@@ -28,6 +28,7 @@ from .sqla_compat import has_computed
 from .sqla_compat import sqla_13
 from .sqla_compat import sqla_14
 from .sqla_compat import sqla_1x
+from .sqla_compat import sqla_2
 
 
 if not sqla_13:
diff --git a/alembic/util/sqla_compat.py b/alembic/util/sqla_compat.py
index 23255be..9534c99 100644
--- a/alembic/util/sqla_compat.py
+++ b/alembic/util/sqla_compat.py
@@ -23,8 +23,10 @@ from sqlalchemy.schema import Column
 from sqlalchemy.schema import ForeignKeyConstraint
 from sqlalchemy.sql import visitors
 from sqlalchemy.sql.elements import BindParameter
+from sqlalchemy.sql.elements import ColumnClause
 from sqlalchemy.sql.elements import quoted_name
 from sqlalchemy.sql.elements import TextClause
+from sqlalchemy.sql.elements import UnaryExpression
 from sqlalchemy.sql.visitors import traverse
 
 if TYPE_CHECKING:
@@ -37,7 +39,6 @@ if TYPE_CHECKING:
     from sqlalchemy.sql.base import ColumnCollection
     from sqlalchemy.sql.compiler import SQLCompiler
     from sqlalchemy.sql.dml import Insert
-    from sqlalchemy.sql.elements import ColumnClause
     from sqlalchemy.sql.elements import ColumnElement
     from sqlalchemy.sql.schema import Constraint
     from sqlalchemy.sql.schema import SchemaItem
@@ -60,7 +61,8 @@ _vers = tuple(
 sqla_13 = _vers >= (1, 3)
 sqla_14 = _vers >= (1, 4)
 sqla_14_26 = _vers >= (1, 4, 26)
-sqla_2 = _vers >= (1, 5)
+sqla_2 = _vers >= (2,)
+sqlalchemy_version = __version__
 
 
 if sqla_14:
@@ -556,3 +558,13 @@ else:
 
     def _select(*columns, **kw) -> Select:  # type: ignore[no-redef]
         return sql.select(list(columns), **kw)  # type: ignore[call-overload]
+
+
+def is_expression_index(index: Index) -> bool:
+    expr: Any
+    for expr in index.expressions:
+        while isinstance(expr, UnaryExpression):
+            expr = expr.element
+        if not isinstance(expr, ColumnClause) or expr.is_literal:
+            return True
+    return False