[gcc r15-1510] ada: Fix for Default_Component_Value with declare expressions

[Marc Poulhi?s]

https://gcc.gnu.org/g:a0546a36e007d1def02f5a575d1b4e2a08a66115

commit r15-1510-ga0546a36e007d1def02f5a575d1b4e2a08a66115
Author: Piotr Trojanek <trojanek@adacore.com>
Date:   Thu May 16 10:59:31 2024 +0200

    ada: Fix for Default_Component_Value with declare expressions
    
    When the expression of aspect Default_Component_Value includes a declare
    expression with current type instance, we attempted to recursively froze
    that type, which itself caused an infinite recursion, because we didn't
    properly manage the scope of declare expression.
    
    This patch fixes both the detection of the current type instance and
    analysis of the expression that caused recursive freezing.
    
    gcc/ada/
    
            * sem_attr.adb (In_Aspect_Specification): Use the standard
            condition that works correctly with declare expressions.
            * sem_ch13.adb (Analyze_Aspects_At_Freeze_Point): Replace
            ordinary analysis with preanalysis of spec expressions.

Diff:
---
 gcc/ada/sem_attr.adb |  4 +++-
 gcc/ada/sem_ch13.adb | 12 ++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/gcc/ada/sem_attr.adb b/gcc/ada/sem_attr.adb
index 72f5ab491759..d56c25a79cc8 100644
--- a/gcc/ada/sem_attr.adb
+++ b/gcc/ada/sem_attr.adb
@@ -1843,7 +1843,9 @@ package body Sem_Attr is
                if Nkind (P) = N_Aspect_Specification then
                   return P_Type = Entity (P);
 
-               elsif Nkind (P) in N_Declaration then
+               --  Prevent the search from going too far
+
+               elsif Is_Body_Or_Package_Declaration (P) then
                   return False;
                end if;
 
diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
index 4012932a6f21..a86f774018a3 100644
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -1037,11 +1037,19 @@ package body Sem_Ch13 is
 
          Parent_Type : Entity_Id;
 
+         Save_In_Spec_Expression : constant Boolean := In_Spec_Expression;
+
       begin
          --  Ensure Expr is analyzed so that e.g. all types are properly
-         --  resolved for Find_Type_Reference.
+         --  resolved for Find_Type_Reference. We preanalyze this expression
+         --  as a spec expression (to avoid recursive freezing), while skipping
+         --  resolution (to not fold type self-references, e.g. T'Last).
 
-         Analyze (Expr);
+         In_Spec_Expression := True;
+
+         Preanalyze (Expr);
+
+         In_Spec_Expression := Save_In_Spec_Expression;
 
          --  A self-referential aspect is illegal if it forces freezing the
          --  entity before the corresponding aspect has been analyzed.