fix: ignore duplicate constants in versioned migrations

desloppify/languages/python/detectors/smells_ast/_source_detectors.py

@@ -11,6 +11,12 @@
 
 ConstantLocations = dict[tuple[str, str], list[tuple[str, int]]]
 SmellCounts = dict[str, list[dict[str, object]]]
+_VERSIONED_MIGRATION_DIRECTORY_PAIRS = frozenset(
+    {
+        ("alembic", "versions"),
+        ("migrations", "versions"),
+    }
+)
 
 
 def _is_within(root: Path, candidate: Path) -> bool:
@@ -22,6 +28,17 @@ def _is_within(root: Path, candidate: Path) -> bool:
         return False
 
 
+def _is_versioned_migration_path(filepath: str) -> bool:
+    """Return whether a file is an immutable versioned schema migration."""
+    path_parts = tuple(
+        part.casefold() for part in re.split(r"[\\/]+", filepath) if part
+    )
+    return any(
+        path_parts[index : index + 2] in _VERSIONED_MIGRATION_DIRECTORY_PAIRS
+        for index in range(len(path_parts) - 1)
+    )
+
+
 def collect_module_constants(
     filepath: str,
     content: str,
@@ -32,6 +49,9 @@ def collect_module_constants(
     Only collects UPPER_CASE or _UPPER_CASE names assigned to simple literals
     (dicts, lists, sets, tuples, numbers, strings).
     """
+    if _is_versioned_migration_path(filepath):
+        return
+
     try:
         tree = ast.parse(content, filename=filepath)
     except SyntaxError as exc:

desloppify/languages/python/tests/test_py_smells_crossfile.py

@@ -5,6 +5,9 @@
 
 from desloppify.languages.python.detectors import smells as smells_mod
 from desloppify.languages.python.detectors.smells import detect_smells
+from desloppify.languages.python.detectors.smells_ast._source_detectors import (
+    collect_module_constants,
+)
 
 # ── Helpers ────────────────────────────────────────────────
 
@@ -105,6 +108,31 @@ def test_same_constant_in_two_files(self, tmp_path):
         entries, _ = detect_smells(tmp_path)
         assert "duplicate_constant" in _smell_ids(entries)
 
+    def test_versioned_migration_constant_is_ignored(self, tmp_path):
+        migration_dir = tmp_path / "migrations" / "versions"
+        migration_dir.mkdir(parents=True)
+        (migration_dir / "a1_add_constraint.py").write_text("SHA256_CHECK = 'sql'\n")
+        (tmp_path / "model.py").write_text("SHA256_CHECK = 'sql'\n")
+
+        entries, _ = detect_smells(tmp_path)
+
+        assert "duplicate_constant" not in _smell_ids(entries)
+
+    def test_versioned_migration_paths_are_separator_independent(self):
+        for filepath in (
+            "migrations/versions/a1.py",
+            r"migrations\versions\a1.py",
+            "alembic/versions/a1.py",
+            r"alembic\versions\a1.py",
+        ):
+            constants_by_key = {}
+
+            collect_module_constants(
+                filepath, "SHA256_CHECK = 'sql'\n", constants_by_key
+            )
+
+            assert constants_by_key == {}
+
     def test_different_constants_ok(self, tmp_path):
         (tmp_path / "a.py").write_text("MAX_RETRIES = 3\n")
         (tmp_path / "b.py").write_text("MAX_RETRIES = 5\n")