Remove loops from the graph created by digraph_utils:condensation/1

The function digraph_utils:condensation/1 used to create a digraph
containing loops contradicting the documentation which states that the
created digraph is free of cycles.

Thanks to Kostis Sagonas for finding the bug.

3 files changed, 6 insertions, 7 deletions

diff --git a/lib/stdlib/doc/src/digraph_utils.xml b/lib/stdlib/doc/src/digraph_utils.xml
index e44632bfd2..ef6e1cb46f 100644
--- a/lib/stdlib/doc/src/digraph_utils.xml
+++ b/lib/stdlib/doc/src/digraph_utils.xml
@@ -4,7 +4,7 @@
 <erlref>
   <header>
     <copyright>
-      <year>2000</year><year>2011</year>
+      <year>2000</year><year>2012</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -156,7 +156,7 @@
         <p>Creates a digraph where the vertices are 
   	  the <seealso marker="#strong_components">strongly connected 
 	  components</seealso> of <c><anno>Digraph</anno></c> as returned by
-          <c>strong_components/1</c>. If X and Y are strongly
+          <c>strong_components/1</c>. If X and Y are two different strongly
           connected components, and there exist vertices x and y in X
           and Y respectively such that there is an 
 	  edge <seealso marker="#emanate">emanating</seealso> from x 
diff --git a/lib/stdlib/src/digraph_utils.erl b/lib/stdlib/src/digraph_utils.erl
index e221be15a1..807b5c12a1 100644
--- a/lib/stdlib/src/digraph_utils.erl
+++ b/lib/stdlib/src/digraph_utils.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1999-2011. All Rights Reserved.
+%% Copyright Ericsson AB 1999-2012. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -370,5 +370,5 @@ condense('$end_of_table', _T, _SC, _G, _SCG, _I2C) ->
 condense(I, T, SC, G, SCG, I2C) ->
     [{_,C}] = ets:lookup(I2C, I),
     digraph:add_vertex(SCG, C),
-    digraph:add_edge(SCG, SC, C),
+    [digraph:add_edge(SCG, SC, C) || C =/= SC],
     condense(ets:next(T, I), T, SC, G, SCG, I2C).
diff --git a/lib/stdlib/test/digraph_utils_SUITE.erl b/lib/stdlib/test/digraph_utils_SUITE.erl
index 12c486c25f..6b554c2fb7 100644
--- a/lib/stdlib/test/digraph_utils_SUITE.erl
+++ b/lib/stdlib/test/digraph_utils_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2000-2011. All Rights Reserved.
+%% Copyright Ericsson AB 2000-2012. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -211,8 +211,7 @@ condensation(Config) when is_list(Config) ->
 			{lists:sort(V1), lists:sort(V2)} 
 		end,
     ?line Es = lists:map(Fun, digraph:edges(CG)),
-    ?line [{[b],[c]},{[b],[d]},{[e,f,g],[e,f,g]},{[h],[h]},{[i,j],[i,j]}] =
-	lists:sort(Es),
+    ?line [{[b],[c]},{[b],[d]}] = lists:sort(Es),
     ?line true = digraph:delete(CG),
     ?line true = digraph:delete(G),
     ok.