[gcc r14-1964] ada: Fix type derivation of subtype of derived type

[Marc Poulhi?s <dkm@gcc.gnu.org>]

https://gcc.gnu.org/g:ca27b8a030746d09ea61de62e1f3bc1337ebe737

commit r14-1964-gca27b8a030746d09ea61de62e1f3bc1337ebe737
Author: Marc Poulhiès <poulhies@adacore.com>
Date:   Mon May 22 13:59:05 2023 +0200

    ada: Fix type derivation of subtype of derived type
    
    Deriving from a subtype of a derived type of a private type, whose full
    view is itself a derived type of a discriminated record with a known
    discriminatant was failing with the error message:
    
      invalid constraint: type has no discriminant
    
    The compiler needs to use the full view to be able to constrain the
    type.
    
    Also fix minor typo in comments.
    
    gcc/ada/
    
            * sem_ch3.adb (Build_Derived_Record_Type): Use full view as
            Parent_Base if needed.

Diff:
---
 gcc/ada/sem_ch3.adb | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/gcc/ada/sem_ch3.adb b/gcc/ada/sem_ch3.adb
index a0677114288..b9302aae2a9 100644
--- a/gcc/ada/sem_ch3.adb
+++ b/gcc/ada/sem_ch3.adb
@@ -5540,7 +5540,7 @@ package body Sem_Ch3 is
       --  avoided here, when the created subtype declaration is analyzed. (See
       --  Build_Derived_Types)
 
-      --  This also happens when the full view of a private type is derived
+      --  This also happens when the full view of a private type is a derived
       --  type with constraints. In this case the entity has been introduced
       --  in the private declaration.
 
@@ -8669,7 +8669,7 @@ package body Sem_Ch3 is
 
    --  5. FIRST TRANSFORMATION FOR DERIVED RECORDS
    --
-   --  Regardless of whether we dealing with a tagged or untagged type
+   --  Regardless of whether we are dealing with a tagged or untagged type
    --  we will transform all derived type declarations of the form
    --
    --               type T is new R (...) [with ...];
@@ -9056,6 +9056,36 @@ package body Sem_Ch3 is
          Parent_Base := Base_Type (Parent_Base);
       end if;
 
+      --  If the parent base is a private type and only its full view has
+      --  discriminants, use the full view's base type.
+
+      --  This can happen when we are deriving from a subtype of a derived type
+      --  of a private type derived from a discriminated type with known
+      --  discriminant:
+      --
+      --  package Pkg;
+      --     type Root_Type(I: Positive) is record
+      --       ...
+      --     end record;
+      --     type Bounded_Root_Type is private;
+      --  private
+      --     type Bounded_Root_Type is new Root_Type(10);
+      --  end Pkg;
+      --
+      --  package Pkg2 is
+      --     type Constrained_Root_Type is new Pkg.Bounded_Root_Type;
+      --  end Pkg2;
+      --  subtype Sub_Base is Pkg2.Constrained_Root_Type;
+      --  type New_Der_Type is new Sub_Base;
+
+      if Is_Private_Type (Parent_Base)
+        and then Present (Full_View (Parent_Base))
+        and then not Has_Discriminants (Parent_Base)
+        and then Has_Discriminants (Full_View (Parent_Base))
+      then
+         Parent_Base := Base_Type (Full_View (Parent_Base));
+      end if;
+
       --  AI05-0115: if this is a derivation from a private type in some
       --  other scope that may lead to invisible components for the derived
       --  type, mark it accordingly.
@@ -9287,7 +9317,7 @@ package body Sem_Ch3 is
             Is_Completion => False, Derive_Subps => False);
 
          --  ??? This needs re-examination to determine whether the
-         --  above call can simply be replaced by a call to Analyze.
+         --  following call can simply be replaced by a call to Analyze.
 
          Set_Analyzed (New_Decl);