fix(mssql): stop capturing a known connection-failure class in validate_credentials

products/warehouse_sources/backend/temporal/data_imports/sources/mssql/source.py

@@ -58,6 +58,8 @@
     "publicly, use the SSH tunnel option."
 )
 
+_GENERIC_CONNECTION_ERROR = "Could not connect to MS SQL. Please check all connection details are valid."
+
 MSSQLErrors = {
     # SQL Server error 18456 is an authentication failure (wrong username/password, or the login is
     # disabled), not a problem with the database field. Surface the same wording the sibling SQL
@@ -68,6 +70,11 @@
     # message echoes the server name and client IP, so match the stable, distinctive phrase instead.
     "is not allowed to access the server": _FIREWALL_BLOCKED_ERROR,
     "connection timed out": _CONNECTION_TIMED_OUT_ERROR,
+    # DB-Lib error 20002, the generic connect-time failure `get_non_retryable_errors` below also
+    # matches (and leaves unmapped there since the cause varies). Map it here too so a credential
+    # check that hits it returns the same generic guidance as an unmatched error already gets,
+    # instead of falling through to `capture_exception` as a bug.
+    "Adaptive Server connection failed": _GENERIC_CONNECTION_ERROR,
 }
 
 _MSSQL_IMPLEMENTATION = MSSQLImplementation()
@@ -372,7 +379,7 @@ def validate_credentials(
                     return False, value
 
             capture_exception(e)
-            return False, "Could not connect to MS SQL. Please check all connection details are valid."
+            return False, _GENERIC_CONNECTION_ERROR
         except BaseSSHTunnelForwarderError as e:
             return (
                 False,
@@ -381,6 +388,6 @@ def validate_credentials(
             )
         except Exception as e:
             capture_exception(e)
-            return False, "Could not connect to MS SQL. Please check all connection details are valid."
+            return False, _GENERIC_CONNECTION_ERROR
 
         return True, None

products/warehouse_sources/backend/temporal/data_imports/sources/mssql/tests/test_mssql.py

@@ -34,6 +34,7 @@
 )
 from products.warehouse_sources.backend.temporal.data_imports.sources.mssql.source import (
     _FIREWALL_BLOCKED_ERROR,
+    _GENERIC_CONNECTION_ERROR,
     MSSQLSource,
 )
 from products.warehouse_sources.backend.types import IncrementalFieldType
@@ -674,6 +675,26 @@ def test_firewall_block_returns_actionable_message_without_capturing(self, sourc
         assert error == _FIREWALL_BLOCKED_ERROR
         capture.assert_not_called()
 
+    def test_adaptive_server_connection_failed_returns_generic_message_without_capturing(self, source, mocker):
+        capture = mocker.patch(
+            "products.warehouse_sources.backend.temporal.data_imports.sources.mssql.source.capture_exception"
+        )
+        mocker.patch.object(source, "is_database_host_valid", return_value=(True, None))
+        # Real DB-Lib 20017/20002 pair: the server closed the connection mid-handshake, which
+        # FreeTDS reports as both an EOF and a generic "connection failed".
+        dropped_connection_error = pymssql.OperationalError(
+            20017,
+            b"DB-Lib error message 20017, severity 9:\nUnexpected EOF from the server (127.0.0.1)\n"
+            b"DB-Lib error message 20002, severity 9:\nAdaptive Server connection failed (127.0.0.1)\n",
+        )
+        mocker.patch.object(source, "get_schemas", side_effect=dropped_connection_error)
+
+        valid, error = source.validate_credentials(_make_config(), team_id=1)
+
+        assert valid is False
+        assert error == _GENERIC_CONNECTION_ERROR
+        capture.assert_not_called()
+
     @pytest.mark.parametrize(
         ("driver_error", "expected_guidance"),
         [