Chore!: add migration script to warn about dbt data_type-related diffs

Author: georgesittas

sqlmesh/migrations/v0092_warn_about_dbt_data_type_diff.py

@@ -0,0 +1,43 @@
+"""
+Warns dbt users about potential diffs due to corrected data_type handling.
+
+SQLMesh previously treated dbt's schema.yml data_type field as columns_to_types, which
+doesn't match dbt's behavior. dbt only uses data_type for contracts/validation, not DDL.
+This fix may cause diffs if tables were created with incorrect types.
+
+More context: https://github.com/TobikoData/sqlmesh/pull/5231
+"""
+
+import json
+
+from sqlglot import exp
+
+from sqlmesh.core.console import get_console
+
+
+def migrate(state_sync, **kwargs):  # type: ignore
+    engine_adapter = state_sync.engine_adapter
+    schema = state_sync.schema
+    snapshots_table = "_snapshots"
+    if schema:
+        snapshots_table = f"{schema}.{snapshots_table}"
+
+    warning = (
+        "IMPORTANT: this migration may have unexpected side-effects for dbt projects.\n\n"
+        "SQLMesh previously misinterpreted dbt's schema.yml 'data_type' field as actual "
+        "column types, but dbt only uses these for contracts/validation, not in actual DDL statements. This "
+        "has been fixed to match dbt's actual behavior. Your existing tables may have been created with "
+        "incorrect column types. After this migration, run 'sqlmesh diff prod' to check for column "
+        "type differences, and if any are found, apply a plan to correct the table schemas. "
+        "For more details, see: https://github.com/TobikoData/sqlmesh/pull/5231."
+    )
+
+    for (snapshot,) in engine_adapter.fetchall(
+        exp.select("snapshot").from_(snapshots_table), quote_identifiers=True
+    ):
+        parsed_snapshot = json.loads(snapshot)
+        node = parsed_snapshot["node"]
+
+        if node.get("columns"):
+            get_console().log_warning(warning)
+            return