An operation declared in the private part of a generic package is overriding
in an instane only if it was overriding in the generic. If an instantiation
fails because a non-abstract type has a remaining abstract inherited operation
it may be because of a failure to override. This patch produces a warning in
this case, that clarifies the resulting error message.
compiling inst.ads must yield:
inst.ads:5:04: instantiation error at gen.ads:7
inst.ads:5:04: type must be declared abstract or "Change" overridden
inst.ads:5:04: "Change" has been inherited at gen.ads:5, instance at line 5
inst.ads:5:04: "Change" has been inherited from subprogram at line 4
inst.ads:5:04: warning: in instantiation at gen.ads:8
inst.ads:5:04: warning: private operation "Change" in generic unit does not
override any primitive operation of "Der" (RM 12.3 (18))
---
with P1; with Gen;
package Inst is
type Act is abstract new P1.Root with null record;
procedure Change (Obj : Act) is abstract;
package Prob is new Gen (Act);
end Inst;
---
package P1 is
type Root is abstract tagged null record;
end P1;
---
with P1;
generic
type Ext is abstract new P1.Root with private;
package Gen is
type Der is new Ext with private;
private
type Der is new Ext with null record;
procedure Change (Obj : Der);
end Gen;
Tested on x86_64-pc-linux-gnu, committed on trunk
2012-02-17 Ed Schonberg <[email protected]>
* sem_ch6.adb (Is_Non_Overriding_Operation): Add warning if the
old operation is abstract, the relevant type is not abstract,
and the new subprogram fails to override.
Index: sem_ch6.adb
===================================================================
--- sem_ch6.adb (revision 184330)
+++ sem_ch6.adb (working copy)
@@ -188,9 +188,9 @@
New_E : Entity_Id) return Boolean;
-- Enforce the rule given in 12.3(18): a private operation in an instance
-- overrides an inherited operation only if the corresponding operation
- -- was overriding in the generic. This can happen for primitive operations
- -- of types derived (in the generic unit) from formal private or formal
- -- derived types.
+ -- was overriding in the generic. This needs to be checked for primitive
+ -- operations of types derived (in the generic unit) from formal private
+ -- or formal derived types.
procedure Make_Inequality_Operator (S : Entity_Id);
-- Create the declaration for an inequality operator that is implicitly
@@ -7844,6 +7844,22 @@
-- If no match found, then the new subprogram does not
-- override in the generic (nor in the instance).
+ -- If the type in question is not abstract, and the subprogram
+ -- is, this will be an error if the new operation is in the
+ -- private part of the instance. Emit a warning now, which will
+ -- make the subsequent error message easier to understand.
+
+ if not Is_Abstract_Type (F_Typ)
+ and then Is_Abstract_Subprogram (Prev_E)
+ and then In_Private_Part (Current_Scope)
+ then
+ Error_Msg_Node_2 := F_Typ;
+ Error_Msg_NE
+ ("private operation& in generic unit does not override " &
+ "any primitive operation of& (RM 12.3 (18))?",
+ New_E, New_E);
+ end if;
+
return True;
end;
end if;
