fix: handle annotated assignments (AnnAssign) in migration files

Newer Alembic versions generate `revision: str = '...'` instead of
`revision = '...'`. The AST parser only handled Assign nodes, silently
skipping every migration that used the annotated form.

Closes #4

Author: stephen-kintsugi

squawk_alembic/hook.py

@@ -6,7 +6,7 @@
 import subprocess
 import sys
 import tempfile
-from ast import Assign, Constant, Name, Tuple, iter_child_nodes, parse
+from ast import AnnAssign, Assign, Constant, Name, Tuple, iter_child_nodes, parse
 from configparser import ConfigParser, NoOptionError, NoSectionError
 from pathlib import Path
 
@@ -57,12 +57,16 @@ def extract_revision_info(filepath):
     down_revision = None
 
     for node in iter_child_nodes(tree):
-        if not isinstance(node, Assign):
+        if isinstance(node, AnnAssign):
+            if not isinstance(node.target, Name) or node.value is None:
+                continue
+            name = node.target.id
+        elif isinstance(node, Assign):
+            if len(node.targets) != 1 or not isinstance(node.targets[0], Name):
+                continue
+            name = node.targets[0].id
+        else:
             continue
-        if len(node.targets) != 1 or not isinstance(node.targets[0], Name):
-            continue
-
-        name = node.targets[0].id
         if name == "revision":
             if isinstance(node.value, Constant) and isinstance(node.value.value, str):
                 revision = node.value.value

tests/test_revision_info.py

@@ -85,3 +85,60 @@ def upgrade():
             pass
     """)
     assert extract_revision_info(path) is None
+
+
+def test_annotated_assignment(migration_file):
+    path = migration_file("""
+        from typing import Sequence, Union
+
+        revision: str = 'abc123'
+        down_revision: Union[str, None] = 'def456'
+        branch_labels: Union[str, Sequence[str], None] = None
+        depends_on: Union[str, Sequence[str], None] = None
+
+        def upgrade():
+            pass
+    """)
+    info = extract_revision_info(path)
+    assert info is not None
+    assert info.revision == "abc123"
+    assert info.down_revision == "def456"
+    assert info.is_merge is False
+
+
+def test_annotated_first_migration_down_revision_is_none(migration_file):
+    path = migration_file("""
+        from typing import Sequence, Union
+
+        revision: str = 'abc123'
+        down_revision: Union[str, None] = None
+        branch_labels: Union[str, Sequence[str], None] = None
+        depends_on: Union[str, Sequence[str], None] = None
+
+        def upgrade():
+            pass
+    """)
+    info = extract_revision_info(path)
+    assert info is not None
+    assert info.revision == "abc123"
+    assert info.down_revision is None
+    assert info.is_merge is False
+
+
+def test_annotated_merge_migration(migration_file):
+    path = migration_file("""
+        from typing import Sequence, Union
+
+        revision: str = 'merge001'
+        down_revision: Union[str, None] = ('abc123', 'def456')
+        branch_labels: Union[str, Sequence[str], None] = None
+        depends_on: Union[str, Sequence[str], None] = None
+
+        def upgrade():
+            pass
+    """)
+    info = extract_revision_info(path)
+    assert info is not None
+    assert info.revision == "merge001"
+    assert info.down_revision == ("abc123", "def456")
+    assert info.is_merge is True