[Ada] Dangling cursor checks in Element function

In Ada.Containers.Ordered_Maps, if a dangling cursor is passed to the Element
function, execution is erroneous. Therefore, the compiler is not obligated to
detect this error. However, this patch inserts code that will detect this error
in some cases, and raise Program_Error. The same applies to Ordered_Sets,
Ordered_Multisets, Indefinite_Ordered_Maps, Indefinite_Ordered_Sets, and
Indefinite_Ordered_Multisets. No test available for erroneous execution.

2018-06-11  Bob Duff  <duff@adacore.com>

gcc/ada/

	* libgnat/a-ciorma.adb, libgnat/a-ciormu.adb, libgnat/a-ciorse.adb,
	libgnat/a-coorma.adb, libgnat/a-coormu.adb, libgnat/a-coorse.adb:
	(Element): Add code to detect dangling cursors in some cases.

From-SVN: r261424

gcc/ada/ChangeLog

+2018-06-11  Bob Duff  <duff@adacore.com>
+
+	* libgnat/a-ciorma.adb, libgnat/a-ciormu.adb, libgnat/a-ciorse.adb,
+	libgnat/a-coorma.adb, libgnat/a-coormu.adb, libgnat/a-coorse.adb:
+	(Element): Add code to detect dangling cursors in some cases.
+
 2018-06-11  Yannick Moy  <moy@adacore.com>
 
 	* sem_ch6.adb (Build_Subprogram_Declaration): Mark parameters as coming

gcc/ada/libgnat/a-ciorma.adb

@@ -541,6 +541,13 @@ package body Ada.Containers.Indefinite_Ordered_Maps is
            "Position cursor of function Element is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "Position cursor of function Element is bad");
 

gcc/ada/libgnat/a-ciormu.adb

@@ -545,6 +545,13 @@ package body Ada.Containers.Indefinite_Ordered_Multisets is
          raise Program_Error with "Position cursor is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 

gcc/ada/libgnat/a-ciorse.adb

@@ -534,6 +534,13 @@ package body Ada.Containers.Indefinite_Ordered_Sets is
          raise Program_Error with "Position cursor is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 

gcc/ada/libgnat/a-coorma.adb

@@ -481,6 +481,13 @@ package body Ada.Containers.Ordered_Maps is
            "Position cursor of function Element equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "Position cursor of function Element is bad");
 

gcc/ada/libgnat/a-coormu.adb

@@ -502,6 +502,13 @@ package body Ada.Containers.Ordered_Multisets is
          raise Constraint_Error with "Position cursor equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 

gcc/ada/libgnat/a-coorse.adb

@@ -480,6 +480,13 @@ package body Ada.Containers.Ordered_Sets is
          raise Constraint_Error with "Position cursor equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");