typing: include a hook to enable more precise error information on 'expected expressi...

[nit.git] / src / semantize / typing.nit

diff --git a/src/semantize/typing.nit b/src/semantize/typing.nit
index aeb3b7e..ddc87e2 100644 (file)
--- a/src/semantize/typing.nit
+++ b/src/semantize/typing.nit
@@ -152,7 +152,11 @@ private class TypeVisitor
                        end
                        return null # forward error
                end
-               self.error(nexpr, "Error: expected an expression.")
+               var more_message = null
+               var p = nexpr.parent
+               if p != null then more_message = p.bad_expr_message(nexpr)
+               if more_message == null then more_message = "" else more_message = " " + more_message
+               self.error(nexpr, "Error: expected an expression{more_message}.")
                return null
        end
 
@@ -802,6 +806,12 @@ end
 
 redef class ANode
        private fun accept_post_typing(v: TypeVisitor) do end
+
+       # An additional information message to explain the role of a child expression.
+       #
+       # The point of the method is to allow some kind of double dispatch so the parent
+       # choose how to describe its children.
+       private fun bad_expr_message(child: AExpr): nullable String do return null
 end
 
 redef class AAttrPropdef
@@ -1710,6 +1720,14 @@ redef class ASendExpr
        # The property invoked by the send.
        var callsite: nullable CallSite
 
+       redef fun bad_expr_message(child)
+       do
+               if child == self.n_expr then
+                       return "to be the receiver of `{self.property_name}`"
+               end
+               return null
+       end
+
        redef fun accept_typing(v)
        do
                var nrecv = self.n_expr