fix: prevent default catalog leak into catalog-unsupported gateways

Fixes #5748

When the default gateway has a default catalog set (e.g., Trino with
catalog: example_catalog), that catalog was silently prepended to model
names targeting secondary gateways that do not support catalogs (e.g.,
ClickHouse), causing UnsupportedCatalogOperationError at evaluation time.

The per-gateway catalog dict omits catalog-unsupported gateways entirely,
so the model loader could not distinguish "no catalog" from "not checked"
and fell through to the global default. This change explicitly sets
default_catalog to None when a gateway is known but absent from the dict.

Signed-off-by: Michael Day <michael.day@cloudkitchens.com>

Author: michaeldayCK

sqlmesh/core/model/definition.py

@@ -2083,12 +2083,15 @@ def create_models_from_blueprints(
         else:
             gateway_name = None
 
-        if (
-            default_catalog_per_gateway
-            and gateway_name
-            and (catalog := default_catalog_per_gateway.get(gateway_name)) is not None
-        ):
-            loader_kwargs["default_catalog"] = catalog
+        if default_catalog_per_gateway and gateway_name:
+            catalog = default_catalog_per_gateway.get(gateway_name)
+            if catalog is not None:
+                loader_kwargs["default_catalog"] = catalog
+            else:
+                # Gateway exists but has no entry in the dict (e.g., catalog-unsupported
+                # engines like ClickHouse). Clear the default catalog so the global
+                # default from the primary gateway doesn't leak into this model's name.
+                loader_kwargs["default_catalog"] = None
 
         model_blueprints.append(
             loader(

tests/core/test_catalog_leak.py

@@ -0,0 +1,122 @@
+"""
+Test: Default gateway catalog should not leak into catalog-unsupported secondary gateways.
+
+Regression test for https://github.com/TobikoData/sqlmesh/issues/5748
+
+When the default gateway has a default catalog set (e.g., Trino with catalog: example_catalog),
+that catalog should not be prepended to model names targeting secondary gateways that do not
+support catalogs (e.g., ClickHouse).
+"""
+
+from sqlglot import parse
+
+from sqlmesh.core.model import load_sql_based_model
+from sqlmesh.core.model.definition import load_sql_based_models
+
+
+def test_default_catalog_not_leaked_to_unsupported_gateway():
+    """
+    When a model targets a gateway that is NOT in default_catalog_per_gateway,
+    the global default_catalog should be cleared (set to None) instead of
+    leaking through from the default gateway.
+    """
+    expressions = parse(
+        """
+        MODEL (
+            name my_schema.my_model,
+            kind FULL,
+            gateway clickhouse_gw,
+            dialect clickhouse,
+        );
+
+        SELECT 1 AS id
+        """,
+        read="clickhouse",
+    )
+
+    # default_gw has a catalog, clickhouse_gw is absent because it doesn't support catalogs
+    default_catalog_per_gateway = {
+        "default_gw": "example_catalog",
+    }
+
+    models = load_sql_based_models(
+        expressions,
+        get_variables=lambda gw: {},
+        dialect="clickhouse",
+        default_catalog_per_gateway=default_catalog_per_gateway,
+        default_catalog="example_catalog",
+    )
+
+    assert len(models) == 1
+    model = models[0]
+
+    assert not model.catalog, (
+        f"Default gateway catalog leaked into catalog-unsupported gateway model. "
+        f"Expected no catalog, got: {model.catalog}"
+    )
+    assert "example_catalog" not in model.fqn, (
+        f"Default gateway catalog found in model FQN: {model.fqn}"
+    )
+
+
+def test_default_catalog_still_applied_to_supported_gateway():
+    """
+    Control test: when a model targets a gateway that IS in default_catalog_per_gateway,
+    the catalog should still be correctly applied.
+    """
+    expressions = parse(
+        """
+        MODEL (
+            name my_schema.my_model,
+            kind FULL,
+            gateway other_duckdb,
+        );
+
+        SELECT 1 AS id
+        """,
+        read="duckdb",
+    )
+
+    default_catalog_per_gateway = {
+        "default_gw": "example_catalog",
+        "other_duckdb": "other_db",
+    }
+
+    models = load_sql_based_models(
+        expressions,
+        get_variables=lambda gw: {},
+        dialect="duckdb",
+        default_catalog_per_gateway=default_catalog_per_gateway,
+        default_catalog="example_catalog",
+    )
+
+    assert len(models) == 1
+    model = models[0]
+
+    assert model.catalog == "other_db", f"Expected catalog 'other_db', got: {model.catalog}"
+
+
+def test_no_gateway_uses_global_default_catalog():
+    """
+    Control test: when a model does NOT specify a gateway, the global
+    default_catalog should still be applied as before.
+    """
+    expressions = parse(
+        """
+        MODEL (
+            name my_schema.my_model,
+            kind FULL,
+        );
+
+        SELECT 1 AS id
+        """,
+        read="duckdb",
+    )
+
+    model = load_sql_based_model(
+        expressions,
+        default_catalog="example_catalog",
+        dialect="duckdb",
+    )
+
+    assert model.catalog == "example_catalog"