syntax: warning for useless 'isa' and 'as' type checks

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/syntax/typing.nit b/src/syntax/typing.nit
index fdb8867..512288d 100644 (file)
--- a/src/syntax/typing.nit
+++ b/src/syntax/typing.nit
@@ -1464,9 +1464,26 @@ redef class AClosureDef
        end
 end
 
+class ATypeCheckExpr
+special PExpr
+       private meth check_expr_cast(v: TypingVisitor, n_expr: PExpr, n_type: PType)
+       do
+               if not v.check_expr(n_expr) then return
+               var etype = n_expr.stype
+               var ttype = n_type.stype
+               if etype == ttype then
+                       v.warning(self, "Warning: Expression is already a {ttype}.")
+               else if etype < ttype then
+                       v.warning(self, "Warning: Expression is already a {ttype} since it is a {etype}.")
+               end
+       end
+end
+
 redef class AIsaExpr
+special ATypeCheckExpr
        redef meth after_typing(v)
        do
+               check_expr_cast(v, n_expr, n_type)
                var variable = n_expr.its_variable
                if variable != null then
                        _if_true_variable_ctx = v.variable_ctx.sub_with(variable, n_type.stype)
@@ -1477,9 +1494,10 @@ redef class AIsaExpr
 end
 
 redef class AAsCastExpr
+special ATypeCheckExpr
        redef meth after_typing(v)
        do
-               v.check_expr(n_expr)
+               check_expr_cast(v, n_expr, n_type)
                _stype = n_type.stype
                _is_typed = _stype != null
        end