Lkt lowering: handle cast expressions

TN: RA22-015

Author: pmderodat

langkit/lkt_lowering.py

@@ -26,7 +26,7 @@
 )
 import langkit.expressions as E
 from langkit.expressions import (
-    AbstractExpression, AbstractProperty, AbstractVariable, Property,
+    AbstractExpression, AbstractProperty, AbstractVariable, Cast, Property,
     PropertyDef
 )
 from langkit.lexer import (
@@ -1602,6 +1602,14 @@ def lower_args() -> Tuple[List[AbstractExpression],
                 ]
                 return E.IsA(subexpr, *nodes)
 
+            elif isinstance(expr, L.CastExpr):
+                subexpr = lower(expr.f_expr)
+                excludes_null = expr.f_excludes_null.p_as_bool
+                dest_type = self.resolve_type_decl(
+                    expr.f_dest_type.p_designated_type
+                )
+                return Cast(subexpr, dest_type, do_raise=excludes_null)
+
             elif isinstance(expr, L.NotExpr):
                 return E.Not(lower(expr.f_expr))
 

testsuite/tests/properties/analysis_unit/test.py

@@ -43,5 +43,5 @@ class Plus(Expression):
 
 
 build_and_run(lkt_file='expected_concrete_syntax.lkt', py_script='main.py',
-              lkt_semantic_checks=True)
+              types_from_lkt=True)
 print('Done')