[Ada] Missing error on illegal reference to Part_Of constituent

[Ada] Missing error on illegal reference to Part_Of constituent

[Arnaud Charlet]

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This patch corrects the mechanism which verifies the legality of references to
variables and constants acting as Part_Of constituents of single protected or
task types to continue examining the context of the reference when it appears
in an expression function.

------------
-- Source --
------------

--  prot.ads

package Prot with SPARK_Mode is
   protected P is
   end P;

   function Func return Boolean;
private
   G : Boolean := False with Part_Of => P;
end Prot;

--  prot.adb

package body Prot with SPARK_Mode is
   protected body P is
   end P;

   function Flip return Boolean is (G);

   function Func return Boolean is
   begin
      return G;
   end Func;
end Prot;

----------------------------
-- Compilation and output --
----------------------------

$ gcc -c prot.adb
prot.adb:5:37: reference to variable "G" cannot appear in this context
prot.adb:5:37: "G" is constituent of single task type "P"
prot.adb:9:14: reference to variable "G" cannot appear in this context
prot.adb:9:14: "G" is constituent of single task type "P"

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

2017-04-25  Hristian Kirtchev  <kirtchev@adacore.com>

	* sem_util.adb (Check_Part_Of_Reference):
	Continue to examine the context if the reference appears within
	an expression function.


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Index: sem_util.adb
===================================================================
--- sem_util.adb	(revision 247151)
+++ sem_util.adb	(working copy)
@@ -1823,9 +1823,21 @@
                               N_Subprogram_Declaration)
            and then not Comes_From_Source (Par)
          then
-            OK_Use := True;
-            exit;
+            --  Continue to examine the context if the reference appears in a
+            --  subprogram body which was previously an expression function.
 
+            if Nkind (Par) = N_Subprogram_Body
+              and then Was_Expression_Function (Par)
+            then
+               null;
+
+            --  Otherwise the reference is legal
+
+            else
+               OK_Use := True;
+               exit;
+            end if;
+
          --  The reference has been relocated to an inlined body for GNATprove.
          --  Assume that the reference is legal as the real check was already
          --  performed in the original context of the reference.