[Ada] Reject illegal syntax in pragma Contract_Cases

[Pierre-Marie de Rodat]

In pragma Contract_Cases argument only "CASE_GUARD => CONSEQUENCE"
clauses are allowed. Once we know that the pragma argument is an
N_Aggregate, we checked if it has component associations; now we also
check that it has no expressions.

Same for the argument of the Subprogram_Variant contract, whose
implementation was heavily inspired by the Contract_Cases contract.

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

gcc/ada/

        * contracts.adb (Analyze_Entry_Or_Subprogram_Contract,
        Analyze_Subprogram_Body_Stub_Contract): Fix missing references
        to Subprogram_Variant where similar references to Contract_Cases
        are present.
        * sem_prag.adb (Analyze_Contract_Case, Analyze_Variant): Check
        that aggregate parameter has no expressions.
        (Analyze_Pragma): Replace Contract_Cases with Subprogram_Variant
        in a copy-pasted comment.
diff --git a/gcc/ada/contracts.adb b/gcc/ada/contracts.adb
--- a/gcc/ada/contracts.adb
+++ b/gcc/ada/contracts.adb
@@ -668,7 +668,7 @@ package body Contracts is
             end;
          end if;
 
-         --  Analyze contract-cases and test-cases
+         --  Analyze contract-cases, subprogram-variant and test-cases
 
          Prag := Contract_Test_Cases (Items);
          while Present (Prag) loop
@@ -1432,6 +1432,7 @@ package body Contracts is
       --    Global
       --    Postcondition
       --    Precondition
+      --    Subprogram_Variant
       --    Test_Case
 
       else


diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
--- a/gcc/ada/sem_prag.adb
+++ b/gcc/ada/sem_prag.adb
@@ -549,7 +549,11 @@ package body Sem_Prag is
 
       pragma Assert (Nkind (CCases) = N_Aggregate);
 
-      if Present (Component_Associations (CCases)) then
+      --  Only CASE_GUARD => CONSEQUENCE clauses are allowed
+
+      if Present (Component_Associations (CCases))
+        and then No (Expressions (CCases))
+      then
 
          --  Ensure that the formal parameters are visible when analyzing all
          --  clauses. This falls out of the general rule of aspects pertaining
@@ -23900,7 +23904,7 @@ package body Sem_Prag is
             Ensure_Aggregate_Form (Get_Argument (N, Spec_Id));
 
             --  Chain the pragma on the contract for further processing by
-            --  Analyze_Contract_Cases_In_Decl_Part.
+            --  Analyze_Subprogram_Variant_In_Decl_Part.
 
             Add_Contract_Item (N, Defining_Entity (Subp_Decl));
 
@@ -29048,7 +29052,11 @@ package body Sem_Prag is
 
       pragma Assert (Nkind (Variants) = N_Aggregate);
 
-      if Present (Component_Associations (Variants)) then
+      --  Only "change_direction => discrete_expression" clauses are allowed
+
+      if Present (Component_Associations (Variants))
+        and then No (Expressions (Variants))
+      then
 
          --  Ensure that the formal parameters are visible when analyzing all
          --  clauses. This falls out of the general rule of aspects pertaining