fix: guard Db2EngineAdapter import on db2-sqlglot-dialect presence, not just Python version

Author: iawanish

sqlmesh/core/engine_adapter/__init__.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import importlib.util
 import sys
 import typing as t
 
@@ -23,8 +24,16 @@
 from sqlmesh.core.engine_adapter.risingwave import RisingwaveEngineAdapter
 from sqlmesh.core.engine_adapter.fabric import FabricEngineAdapter
 
-# DB2 adapter requires Python 3.10+ for db2-sqlglot-dialect
-if sys.version_info >= (3, 10):
+# DB2 adapter requires Python 3.10+ AND db2-sqlglot-dialect to be installed.
+# The dialect package registers "db2" with sqlglot at import time; without it,
+# class-level exp.DataType.build(dialect="db2") in db2.py raises
+# ValueError("Unknown dialect 'db2'") and crashes every non-db2 environment
+# (e.g. the dbt-1.6 test run which installs without the db2 extra).
+_DB2_AVAILABLE = (
+    sys.version_info >= (3, 10)
+    and importlib.util.find_spec("db2_sqlglot") is not None
+)
+if _DB2_AVAILABLE:
     from sqlmesh.core.engine_adapter.db2 import Db2EngineAdapter
 
 DIALECT_TO_ENGINE_ADAPTER = {
@@ -46,8 +55,8 @@
     "starrocks": StarRocksEngineAdapter,
 }
 
-# Add DB2 only on Python 3.10+
-if sys.version_info >= (3, 10):
+# Add DB2 to the registry only when the dialect package is present
+if _DB2_AVAILABLE:
     DIALECT_TO_ENGINE_ADAPTER["db2"] = Db2EngineAdapter
 
 DIALECT_ALIASES = {