[Ada] Accept calls to abstract subprograms in class-wide pre/post-conditions

[Ada] Accept calls to abstract subprograms in class-wide pre/post-conditions

[Pierre-Marie de Rodat]

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Fix a regression in the support for Ada 2022's treatment of calls to
abstract subprograms in pre/post-conditions (thanks to Javier Miranda
for producing this patch).

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_disp.adb (Check_Dispatching_Context): When checking to see
	whether an expression occurs in a class-wide pre/post-condition,
	also check for the possibility that it occurs in a class-wide
	preconditions subprogram that was introduced as part of
	expansion. Without this fix, some legal calls occuring in
	class-wide preconditions may be incorrectly flagged as violating
	the "a call to an abstract subprogram must be dispatching" rule.

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diff --git a/gcc/ada/sem_disp.adb b/gcc/ada/sem_disp.adb
--- a/gcc/ada/sem_disp.adb
+++ b/gcc/ada/sem_disp.adb
@@ -751,14 +751,22 @@ package body Sem_Disp is
 
             elsif Is_Subprogram (Scop)
               and then not Is_Tag_Indeterminate (N)
-              and then In_Pre_Post_Condition (Call, Class_Wide_Only => True)
+              and then
+               --  The context is an internally built helper or an indirect
+               --  call wrapper that handles class-wide preconditions
+                 (Present (Class_Preconditions_Subprogram (Scop))
 
-              --  The tagged type associated with the called subprogram must be
-              --  the same as that of the subprogram with a class-wide aspect.
+               --  ... or the context is a class-wide pre/postcondition.
+                   or else
+                     (In_Pre_Post_Condition (Call, Class_Wide_Only => True)
 
-              and then Is_Dispatching_Operation (Scop)
-              and then
-                Find_Dispatching_Type (Subp) = Find_Dispatching_Type (Scop)
+                       --  The tagged type associated with the called
+                       --  subprogram must be the same as that of the
+                       --  subprogram with a class-wide aspect.
+
+                       and then Is_Dispatching_Operation (Scop)
+                       and then Find_Dispatching_Type (Subp)
+                                  = Find_Dispatching_Type (Scop)))
             then
                null;