Fix: Normalize when_matched and merge_filter expressions to the source dialect

sqlmesh/core/dialect.py

@@ -1388,17 +1388,27 @@ def is_meta_expression(v: t.Any) -> bool:
     return isinstance(v, (Audit, Metric, Model))
 
 
-def replace_merge_table_aliases(expression: exp.Expression) -> exp.Expression:
+def replace_merge_table_aliases(
+    expression: exp.Expression, dialect: t.Optional[str] = None
+) -> exp.Expression:
     """
     Resolves references from the "source" and "target" tables (or their DBT equivalents)
     with the corresponding SQLMesh merge aliases (MERGE_SOURCE_ALIAS and MERGE_TARGET_ALIAS)
     """
     from sqlmesh.core.engine_adapter.base import MERGE_SOURCE_ALIAS, MERGE_TARGET_ALIAS
 
+    normalized_merge_source_alias = quote_identifiers(
+        normalize_identifiers(exp.to_identifier(MERGE_SOURCE_ALIAS), dialect), dialect=dialect
+    )
+
+    normalized_merge_target_alias = quote_identifiers(
+        normalize_identifiers(exp.to_identifier(MERGE_TARGET_ALIAS), dialect), dialect=dialect
+    )
+
     if isinstance(expression, exp.Column) and (first_part := expression.parts[0]):
         if first_part.this.lower() in ("target", "dbt_internal_dest", "__merge_target__"):
-            first_part.replace(exp.to_identifier(MERGE_TARGET_ALIAS))
+            first_part.replace(normalized_merge_target_alias)
         elif first_part.this.lower() in ("source", "dbt_internal_source", "__merge_source__"):
-            first_part.replace(exp.to_identifier(MERGE_SOURCE_ALIAS))
+            first_part.replace(normalized_merge_source_alias)
 
     return expression

sqlmesh/core/model/definition.py

@@ -653,7 +653,7 @@ def render_merge_filter(
         )
         if len(rendered_exprs) != 1:
             raise SQLMeshError(f"Expected one expression but got {len(rendered_exprs)}")
-        return rendered_exprs[0].transform(d.replace_merge_table_aliases)
+        return rendered_exprs[0].transform(d.replace_merge_table_aliases, dialect=self.dialect)
 
     def _render_properties(
         self, properties: t.Dict[str, exp.Expression] | SessionProperties, **render_kwargs: t.Any

sqlmesh/core/model/kind.py

@@ -34,6 +34,7 @@
     get_dialect,
     validate_string,
     positive_int_validator,
+    validate_expression,
 )
 
 
@@ -467,15 +468,20 @@ def _when_matched_validator(
             return v
         if isinstance(v, list):
             v = " ".join(v)
+
+        dialect = get_dialect(info.data)
+
         if isinstance(v, str):
             # Whens wrap the WHEN clauses, but the parentheses aren't parsed by sqlglot
             v = v.strip()
             if v.startswith("("):
                 v = v[1:-1]
 
-            return t.cast(exp.Whens, d.parse_one(v, into=exp.Whens, dialect=get_dialect(info.data)))
+            v = t.cast(exp.Whens, d.parse_one(v, into=exp.Whens, dialect=dialect))
+        else:
+            v = t.cast(exp.Whens, v.transform(d.replace_merge_table_aliases, dialect=dialect))
 
-        return t.cast(exp.Whens, v.transform(d.replace_merge_table_aliases))
+        return validate_expression(v, dialect=dialect)
 
     @field_validator("merge_filter", mode="before")
     def _merge_filter_validator(
@@ -485,11 +491,16 @@ def _merge_filter_validator(
     ) -> t.Optional[exp.Expression]:
         if v is None:
             return v
+
+        dialect = get_dialect(info.data)
+
         if isinstance(v, str):
             v = v.strip()
-            return d.parse_one(v, dialect=get_dialect(info.data))
+            v = d.parse_one(v, dialect=dialect)
+        else:
+            v = v.transform(d.replace_merge_table_aliases, dialect=dialect)
 
-        return v.transform(d.replace_merge_table_aliases)
+        return validate_expression(v, dialect=dialect)
 
     @property
     def data_hash_values(self) -> t.List[t.Optional[str]]:

sqlmesh/migrations/v0084_normalize_quote_when_matched_and_merge_filter.py

@@ -0,0 +1,9 @@
+"""
+Normalize and quote the when_matched and merge_filter properties of IncrementalByUniqueKeyKind
+to match how other properties (such as time_column and partitioned_by) are handled and to
+prevent un-normalized identifiers being quoted at the EngineAdapter level
+"""
+
+
+def migrate(state_sync, **kwargs):  # type: ignore
+    pass

sqlmesh/utils/pydantic.py

@@ -16,6 +16,8 @@
 from sqlmesh.utils import str_to_bool
 
 if t.TYPE_CHECKING:
+    from sqlglot._typing import E
+
     Model = t.TypeVar("Model", bound="PydanticModel")
 
 
@@ -193,6 +195,12 @@ def validate_string(v: t.Any) -> str:
     return str(v)
 
 
+def validate_expression(expression: E, dialect: str) -> E:
+    # this normalizes and quotes identifiers in the given expression according the specified dialect
+    # it also sets expression.meta["dialect"] so that when we serialize for state, the expression is serialized in the correct dialect
+    return _get_field(expression, {"dialect": dialect})  # type: ignore
+
+
 def bool_validator(v: t.Any) -> bool:
     if isinstance(v, exp.Boolean):
         return v.this