From ac8f397160e94f13ea25f941a141a7ce9c3cbc23 Mon Sep 17 00:00:00 2001
From: Tom Clune <tom.clune@nasa.gov>
Date: Tue, 29 May 2018 12:11:06 -0400
Subject: [PATCH] Fix for bug with empty containers.

The value() method previously made illegal references when an iterator
is derived from an empty container.  (E.g., c%find(x)).

This was missed in the unit tests where the iterator was compared
against end().  But we expect value() to behave reasonably even in
this empty case.   Fixes for map, set, and alt_set containers.
---
 include/templates/altSet_impl.inc |  6 +++++-
 include/templates/map_impl.inc    |  6 +++++-
 include/templates/set_impl.inc    |  6 +++++-
 tests/Map/Test_Map.m4             | 10 ++++++++++
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/include/templates/altSet_impl.inc b/include/templates/altSet_impl.inc
index 5b7a030..968f10d 100644
--- a/include/templates/altSet_impl.inc
+++ b/include/templates/altSet_impl.inc
@@ -830,7 +830,11 @@
       class(__iterator), target, intent(in) :: this
       __type_declare_result, pointer :: value
 
-      value=>this%reference%items%at(this%current)
+      if (this%current == UNINITIALIZED) then
+         value => null()
+      else
+         value=>this%reference%items%at(this%current)
+      end if
 
       end function __PROC(value)
 
diff --git a/include/templates/map_impl.inc b/include/templates/map_impl.inc
index 5063ec7..e23beef 100644
--- a/include/templates/map_impl.inc
+++ b/include/templates/map_impl.inc
@@ -332,7 +332,11 @@
          type(__pair), pointer :: p
 
          p => this%setIter%value()
-         res => p%value
+         if (associated(p)) then
+            res => p%value
+         else
+            res => null()
+         end if
 
       end function __PROC(value)
 
diff --git a/include/templates/set_impl.inc b/include/templates/set_impl.inc
index fc65bc9..9ffa962 100644
--- a/include/templates/set_impl.inc
+++ b/include/templates/set_impl.inc
@@ -642,7 +642,11 @@
       class(__iterator), intent(in) :: this
       __type_declare_result, pointer :: value
 
-      value=>this%node%value
+      if (associated(this%node)) then
+         value =>this%node%value
+      else
+         value => null()
+      end if
 
       end function __PROC(value)
 
diff --git a/tests/Map/Test_Map.m4 b/tests/Map/Test_Map.m4
index 15b4246..f2b3b97 100644
--- a/tests/Map/Test_Map.m4
+++ b/tests/Map/Test_Map.m4
@@ -103,6 +103,16 @@ contains
 
    end subroutine test_at
 
+@test
+   subroutine test_value_empty_is_null()
+      type (Map), target :: m
+      type (MapIterator) :: iter
+
+      iter = m%find(KEY1)
+      @assertFalse(associated(iter%value()))
+
+   end subroutine test_value_empty_is_null
+
 @test
    subroutine test_find()
       type (Map), target :: m