[Ada] Improve error message on Extensions_Visible

[Arnaud Charlet]

This patch changes the formatting of errors related to the pragma
 Extensions_Visible so as not to suggest Extensions_Visible applies to a formal
 parameters instead of a subprogram when SPARK RM 6.1.7(3) is violated. In
 addition, a small change to sem_prag was made to make the printing of boolean
 values consistent accross all error messages. 

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

--  ext_vis_error.ads

package Ext_Vis_Error with SPARK_Mode is
   type Root is tagged record
      Comp_1 : Integer := 1;
   end record;

   type Child is new Root with record
      Comp_2 : Integer := 2;
   end record;

   procedure Proc_1 (Obj_C : Child) with Extensions_Visible => False;
   procedure Proc_2 (Obj_C : Child) with Extensions_Visible => True;
end Ext_Vis_Error;

--  ext_vis_error.adb

package body Ext_Vis_Error with SPARK_Mode is
   procedure Proc_1 (Obj_C : Child) is
      Error_1 : constant Root'Class := Obj_C;
      Error_2 : constant Root'Class := Root'Class (Obj_C);

   begin
      Proc_2 (Obj_C);
   end Proc_1;

   procedure Proc_2 (Obj_C : Child) is begin null; end Proc_2;
end Ext_Vis_Error;

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

gcc -c ext_vis_error.adb
gcc -c ext_vis_error.adb -gnatd.F
ext_vis_error.adb:3:40: formal parameter cannot be implicitly converted to
 class-wide type when Extensions_Visible is False
ext_vis_error.adb:4:52: formal parameter cannot be converted to class-wide
 type when Extensions_Visible is False
ext_vis_error.adb:7:15: formal parameter cannot act as actual parameter when
 Extensions_Visible is False
ext_vis_error.adb:7:15: subprogram "Proc_2" has Extensions_Visible True
ext_vis_error.adb:3:40: formal parameter cannot be implicitly converted to
 class-wide type when Extensions_Visible is False
ext_vis_error.adb:4:52: formal parameter cannot be converted to class-wide
 type when Extensions_Visible is False
ext_vis_error.adb:7:15: formal parameter cannot act as actual parameter when
 Extensions_Visible is False
ext_vis_error.adb:7:15: subprogram "Proc_2" has Extensions_Visible True

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

2016-06-14  Justin Squirek  <squirek@adacore.com>

	* sem_ch3.adb (Analyze_Object_Declaration): Fix formatting
	of error output related to SPARK RM 6.1.7(3) and pragma
	Extensions_Visible.
	* sem_ch4.adb (Analyze_Type_Conversion): Fix formatting of error
	output related to SPARK RM 6.1.7(3) and pragma Extensions_Visible.
	* sem_prag.adb (Analyze_Pragma): Fix formatting of error output
	related to SPARK RM 7.1.2(15) and pragma Volatile_Function
	so that the values True and False are no longer surrounded by
	double quotes.
	* sem_res.adb (Resolve_Actuals): Fix formatting of error output
	related to SPARK RM 6.1.7(3) and pragma Extensions_Visible.

-------------- next part --------------
Index: sem_ch3.adb
===================================================================
--- sem_ch3.adb	(revision 237429)
+++ sem_ch3.adb	(working copy)
@@ -3796,8 +3796,8 @@
            and then Is_EVF_Expression (E)
          then
             Error_Msg_N
-              ("formal parameter with Extensions_Visible False cannot be "
-               & "implicitly converted to class-wide type", E);
+              ("formal parameter cannot be implicitly converted to "
+               & "class-wide type when Extensions_Visible is False", E);
          end if;
       end if;
 
Index: sem_prag.adb
===================================================================
--- sem_prag.adb	(revision 237429)
+++ sem_prag.adb	(working copy)
@@ -22821,12 +22821,12 @@
 
                Error_Msg_Sloc := Sloc (Over_Id);
                Error_Msg_N
-                 ("\& declared # with Volatile_Function value `False`",
+                 ("\& declared # with Volatile_Function value False",
                   Spec_Id);
 
                Error_Msg_Sloc := Sloc (Spec_Id);
                Error_Msg_N
-                 ("\overridden # with Volatile_Function value `True`",
+                 ("\overridden # with Volatile_Function value True",
                   Spec_Id);
             end if;
 
Index: sem_res.adb
===================================================================
--- sem_res.adb	(revision 237432)
+++ sem_res.adb	(working copy)
@@ -4596,8 +4596,8 @@
                        Extensions_Visible_True
             then
                Error_Msg_N
-                 ("formal parameter with Extensions_Visible False cannot act "
-                  & "as actual parameter", A);
+                 ("formal parameter cannot act as actual parameter when "
+                  & "Extensions_Visible is False", A);
                Error_Msg_NE
                  ("\subprogram & has Extensions_Visible True", A, Nam);
             end if;
Index: sem_ch4.adb
===================================================================
--- sem_ch4.adb	(revision 237429)
+++ sem_ch4.adb	(working copy)
@@ -5246,8 +5246,8 @@
         and then Is_EVF_Expression (Expr)
       then
          Error_Msg_N
-           ("formal parameter with Extensions_Visible False cannot be "
-            & "converted to class-wide type", Expr);
+           ("formal parameter cannot be converted to class-wide type when "
+            & "Extensions_Visible is False", Expr);
       end if;
    end Analyze_Type_Conversion;