typing: `isa` do not adapt to a supertype.

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

diff --git a/src/semantize/typing.nit b/src/semantize/typing.nit
index 6c4de01..73e1bd0 100644 (file)
--- a/src/semantize/typing.nit
+++ b/src/semantize/typing.nit
@@ -1666,11 +1666,15 @@ redef class AIsaExpr
 
                var variable = self.n_expr.its_variable
                if variable != null then
-                       #var orig = self.n_expr.mtype
+                       var orig = self.n_expr.mtype
                        #var from = if orig != null then orig.to_s else "invalid"
                        #var to = if mtype != null then mtype.to_s else "invalid"
                        #debug("adapt {variable}: {from} -> {to}")
-                       self.after_flow_context.when_true.set_var(v, variable, mtype)
+
+                       # Do not adapt if there is no information gain (i.e. adapt to a supertype)
+                       if mtype == null or orig == null or not v.is_subtype(orig, mtype) then
+                               self.after_flow_context.when_true.set_var(v, variable, mtype)
+                       end
                end
 
                self.mtype = v.type_bool(self)