Fix: Compare columns by using the schema differ based on snapshots dialect (#4595)

Author: themisvaltinos

sqlmesh/core/context.py

@@ -93,7 +93,6 @@
 from sqlmesh.core.plan.definition import UserProvidedFlags
 from sqlmesh.core.reference import ReferenceGraph
 from sqlmesh.core.scheduler import Scheduler, CompletionStatus
-from sqlmesh.core.schema_diff import SchemaDiffer
 from sqlmesh.core.schema_loader import create_external_models_file
 from sqlmesh.core.selector import Selector
 from sqlmesh.core.snapshot import (
@@ -1541,7 +1540,6 @@ def plan_builder(
             ),
             end_bounded=not run,
             ensure_finalized_snapshots=self.config.plan.use_finalized_state,
-            engine_schema_differ=SchemaDiffer(),  # TODO: fix to properly handle it
             interval_end_per_model=max_interval_end_per_model,
             console=self.console,
             user_provided_flags=user_provided_flags,

sqlmesh/core/plan/builder.py

@@ -21,7 +21,11 @@
     UserProvidedFlags,
     earliest_interval_start,
 )
-from sqlmesh.core.schema_diff import SchemaDiffer, has_drop_alteration, get_dropped_column_names
+from sqlmesh.core.schema_diff import (
+    get_schema_differ,
+    has_drop_alteration,
+    get_dropped_column_names,
+)
 from sqlmesh.core.snapshot import (
     DeployabilityIndex,
     Snapshot,
@@ -78,14 +82,12 @@ class PlanBuilder:
         ensure_finalized_snapshots: Whether to compare against snapshots from the latest finalized
             environment state, or to use whatever snapshots are in the current environment state even if
             the environment is not finalized.
-        engine_schema_differ: Schema differ from the context engine adapter.
         interval_end_per_model: The mapping from model FQNs to target end dates.
     """
 
     def __init__(
         self,
         context_diff: ContextDiff,
-        engine_schema_differ: SchemaDiffer,
         start: t.Optional[TimeLike] = None,
         end: t.Optional[TimeLike] = None,
         execution_time: t.Optional[TimeLike] = None,
@@ -137,7 +139,6 @@ def __init__(
         self._backfill_models = backfill_models
         self._end = end or default_end
         self._apply = apply
-        self._engine_schema_differ = engine_schema_differ
         self._console = console or get_console()
         self._choices: t.Dict[SnapshotId, SnapshotChangeCategory] = {}
         self._user_provided_flags = user_provided_flags
@@ -493,7 +494,7 @@ def _check_destructive_changes(self, directly_modified: t.Set[SnapshotId]) -> No
             if columns_to_types_all_known(old_columns_to_types) and columns_to_types_all_known(
                 new_columns_to_types
             ):
-                schema_diff = self._engine_schema_differ.compare_columns(
+                schema_diff = get_schema_differ(snapshot.model.dialect).compare_columns(
                     new.name,
                     old_columns_to_types,
                     new_columns_to_types,

sqlmesh/core/schema_diff.py

@@ -723,5 +723,27 @@ def get_dropped_column_names(alter_expressions: t.List[exp.Alter]) -> t.List[str
     return dropped_columns
 
 
+def get_schema_differ(dialect: str) -> SchemaDiffer:
+    """
+    Returns the appropriate SchemaDiffer for a given dialect without initializing the engine adapter.
+
+    Args:
+        dialect: The dialect for which to get the schema differ.
+
+    Returns:
+        The SchemaDiffer instance configured for the given dialect.
+    """
+    from sqlmesh.core.engine_adapter import (
+        DIALECT_TO_ENGINE_ADAPTER,
+        DIALECT_ALIASES,
+        EngineAdapter,
+    )
+
+    dialect = dialect.lower()
+    dialect = DIALECT_ALIASES.get(dialect, dialect)
+    engine_adapter_class = DIALECT_TO_ENGINE_ADAPTER.get(dialect, EngineAdapter)
+    return getattr(engine_adapter_class, "SCHEMA_DIFFER", SchemaDiffer())
+
+
 def _get_name_and_type(struct: exp.ColumnDef) -> t.Tuple[exp.Identifier, exp.DataType]:
     return struct.this, struct.args["kind"]

tests/core/test_context.py

@@ -279,7 +279,6 @@ def test_diff(sushi_context: Context, mocker: MockerFixture):
 
     plan = PlanBuilder(
         context_diff=sushi_context._context_diff("prod"),
-        engine_schema_differ=sushi_context.engine_adapter.SCHEMA_DIFFER,
     ).build()
 
     # stringify used to trigger an unhashable exception due to