fix(dlt): prevent credential type field overwriting db_type in format_config

format_config initialises config = {"type": db_type} then iterates all
credential object attributes and writes them into config. BigQuery
service-account credentials carry a "type": "service_account" field
(from the GCP service account JSON format) which overwrites the
"bigquery" key. parse_connection_config then raises:

  ConfigError: Unknown connection type 'service_account'

This error fires before model generation starts, even though the direct
caller (generate_dlt_models) discards the connection config entirely.
The bug only surfaces with BigQuery service-account credentials; OAUTH
credentials do not carry a conflicting type field.

Fix: move config["type"] = db_type to after the credential loop so it
cannot be overwritten by credential attributes.

Signed-off-by: Mary Akowe <mary.akowe@madetech.com>

Author: mary-mt

sqlmesh/integrations/dlt.py

@@ -214,9 +214,7 @@ def generate_incremental_model(
 
 def format_config(configs: t.Dict[str, str], db_type: str) -> str:
     """Generate a string for the gateway connection config."""
-    config = {
-        "type": db_type,
-    }
+    config: t.Dict[str, t.Any] = {}
 
     for key, value in configs.items():
         if key == "password":
@@ -226,6 +224,11 @@ def format_config(configs: t.Dict[str, str], db_type: str) -> str:
         else:
             config[key] = value
 
+    # Set db_type after iterating credentials so that credential attributes
+    # with a conflicting name (e.g. GCP service-account JSON contains
+    # "type": "service_account") cannot overwrite the connection type.
+    config["type"] = db_type
+
     # Validate the connection config fields
     invalid_fields = []
     try: