This patch fixes an infinite loop in the compiler when warnings on redundant
constructs are enabled (-gnatwr) and the constructs are use_type clauses
that appear (redundantly) in a parent unit and a child unit.
The following command:
gcc -c -gnatwr root-child.ads
must yield:
root-child.ads:2:01: warning: "Pack.Typ" is already use-visible through
previous use_type_clause at root.ads:2
The following must compile quietly:
gcc -c -gnatwr root-child-grand.ads
----
package Pack is
type Typ is new Integer;
end Pack;
----
with Pack;
use type Pack.Typ;
package Root is
Thing1 : Pack.Typ;
end Root;
----
with pack;
use type pack.typ;
package Root.Child is
Thing2 : Pack.Typ := Root.Thing1 * 3;
end;
----
with Pack;
use type Pack.Typ;
package Root.Child.Grand is
Thing3 : Pack.Typ := Thing1 + Thing2;
end;
Tested on x86_64-pc-linux-gnu, committed on trunk
2018-05-24 Ed Schonberg <schonb...@adacore.com>
gcc/ada/
* sem_ch8.adb (Analyze_Use_Type): Do not assign the Prev_Use_Clause
link to a use_type clause if this would cause an infinite loop in the
machinery that detects redundant use clauses. This may happen when the
redundant clauses appear in the context of a child unit and the context
of its parent.--- gcc/ada/sem_ch8.adb
+++ gcc/ada/sem_ch8.adb
@@ -3916,10 +3916,14 @@ package body Sem_Ch8 is
-- manipulation of the scope stack so we much guard against those cases
-- here, otherwise, we must add the new use_type_clause to the previous
-- use_type_clause chain in order to mark redundant use_type_clauses as
- -- used.
+ -- used. When the redundant use-type clauses appear in a parent unit and
+ -- a child unit we must prevent a circularity in the chain that would
+ -- otherwise result from the separate steps of analysis and installation
+ -- of the parent context.
if Present (Current_Use_Clause (E))
and then Current_Use_Clause (E) /= N
+ and then Prev_Use_Clause (Current_Use_Clause (E)) /= N
and then No (Prev_Use_Clause (N))
then
Set_Prev_Use_Clause (N, Current_Use_Clause (E));
