fix(snowflake): allow loose casting of objects and arrays

ibis/backends/snowflake/registry.py

@@ -4,9 +4,10 @@
 
 import numpy as np
 import sqlalchemy as sa
-from snowflake.sqlalchemy import ARRAY
+from snowflake.sqlalchemy import ARRAY, OBJECT, VARIANT
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.sql import sqltypes
+from sqlalchemy.sql.elements import Cast
 from sqlalchemy.sql.functions import GenericFunction
 
 import ibis.expr.operations as ops
@@ -136,6 +137,29 @@ def _arbitrary(t, op):
     return t._reduction(sa.func.min, op)
 
 
+@compiles(Cast, "snowflake")
+def compiles_cast(element, compiler, **kw):
+    arg = compiler.process(element.clause, **kw)
+    typ = compiler.process(element.type)
+    if typ in ("OBJECT", "ARRAY"):
+        return f"IFF(IS_{typ}({arg}), {arg}, NULL)"
+    return compiler.visit_cast(element, **kw)
+
+
+@compiles(sa.Text, "snowflake")
+@compiles(sa.TEXT, "snowflake")
+@compiles(sa.VARCHAR, "snowflake")
+def compiles_string(element, compiler, **kw):
+    return "VARCHAR"
+
+
+@compiles(OBJECT, "snowflake")
+@compiles(ARRAY, "snowflake")
+@compiles(VARIANT, "snowflake")
+def compiles_object_type(element, compiler, **kw):
+    return type(element).__name__.upper()
+
+
 class _flatten(GenericFunction):
     def __init__(self, arg, *, type: sa.types.TypeEngine) -> None:
         super().__init__(arg)