[gcc r14-3692] ada: Fix spurious warning emissions

[gcc r14-3692] ada: Fix spurious warning emissions

[Marc Poulhi?s]

https://gcc.gnu.org/g:9be6a698f95f94a27307208cdb90bd2018182071

commit r14-3692-g9be6a698f95f94a27307208cdb90bd2018182071
Author: Ronan Desplanques <desplanques@adacore.com>
Date:   Mon Aug 21 13:35:37 2023 +0200

    ada: Fix spurious warning emissions
    
    Before this patch, warnings handled by `Sem_Warn.Check_References` were
    erroneously emitted in some cases. Here is an example of a program that,
    when compiled with the `-gnatwu` switch, triggered the bug:
    
        procedure Main is
           package T is
              A : Integer;
           end T;
        begin
           T.A := 7;
        end Main;
    
    The following message was emitted:
    
       main.adb:3:07: warning: variable "A" is never read and never assigned [-gnatwu]
    
    This patch mitigates the issue by restricting the cases in which
    `Sem_Warn.Check_References` is called for package specifications.
    
    Note that the recursive calls in `Sem_Warn.Check_References` can be used
    to convince oneself that this patch does not remove legitimate warnings
    for non-library-level package specifications.
    
    gcc/ada/
    
            * sem_ch7.adb (Analyze_Package_Declaration): Restrict calls to
            `Sem_Warn.Check_References` and adjust comment accordingly.

Diff:
---
 gcc/ada/sem_ch7.adb | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/gcc/ada/sem_ch7.adb b/gcc/ada/sem_ch7.adb
index ecb4bbe3e569..1a49a53ad63b 100644
--- a/gcc/ada/sem_ch7.adb
+++ b/gcc/ada/sem_ch7.adb
@@ -1267,12 +1267,17 @@ package body Sem_Ch7 is
                Is_Main_Unit => Parent (N) = Cunit (Main_Unit));
          end if;
 
-         --  Warn about references to unset objects, which is straightforward
-         --  for packages with no bodies. For packages with bodies this is more
-         --  complicated, because some of the objects might be set between spec
-         --  and body elaboration, in nested or child packages, etc.
-
-         Check_References (Id);
+         --  For package declarations at the library level, warn about
+         --  references to unset objects, which is straightforward for packages
+         --  with no bodies. For packages with bodies this is more complicated,
+         --  because some of the objects might be set between spec and body
+         --  elaboration, in nested or child packages, etc. Note that the
+         --  recursive calls in Check_References will handle nested package
+         --  specifications.
+
+         if Is_Library_Level_Entity (Id) then
+            Check_References (Id);
+         end if;
       end if;
 
       --  Set Body_Required indication on the compilation unit node