From 757258fb3ac9507a71156b1385a4761efd64aa42 Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Sun, 2 Sep 2018 16:27:56 +0200
Subject: [PATCH] TreeExplorer: fix bug in Filter layer

Fillter needs to be re-evaluated, when an downstream entity requests
expandChildren() onto an upstream source. And obviously the ordering
of the chained calls was wrong here.

As it turns out, I had discovered that necessity to re-evaluate with
the Transformer layer. There is a dedicated test case for that, but
I cut short on verifying the filter in that situation as well, so
that piece of broken copy-n-paste code went through undetected.

This is in fact a rather esoteric corner case, because it is only
triggered when the expandChildren() call is passed through the filter.
When otoh the filter sits /after/ the entity generating the expandChildren()
calls, everything works as intended. And the latter is the typical standard
usage situation of an recursive evalutation algorithm: the filter is here
used as final part to drive the evaluation ahead and pick the solutions.
---
 src/lib/iter-tree-explorer.hpp            |  2 +-
 tests/library/iter-tree-explorer-test.cpp | 14 ++++++++------
 wiki/thinkPad.ichthyo.mm                  |  8 ++++----
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/lib/iter-tree-explorer.hpp b/src/lib/iter-tree-explorer.hpp
index 870747646..650db48cc 100644
--- a/src/lib/iter-tree-explorer.hpp
+++ b/src/lib/iter-tree-explorer.hpp
@@ -885,8 +885,8 @@ namespace lib {
         void
         expandChildren()
           {
-            pullFilter();
             SRC::expandChildren();
+            pullFilter();
           }
         
       public: /* === Iteration control API for IterableDecorator === */
diff --git a/tests/library/iter-tree-explorer-test.cpp b/tests/library/iter-tree-explorer-test.cpp
index 02c5d4021..39e9e08d3 100644
--- a/tests/library/iter-tree-explorer-test.cpp
+++ b/tests/library/iter-tree-explorer-test.cpp
@@ -785,13 +785,15 @@ namespace test{
           
           // contrived example to verify interplay of filtering and child expansion;
           // especially note that the filter is re-evaluated after expansion happened.
-          cout << "VERIFY->"
-               <<materialise(
+          CHECK (materialise (
                     treeExplore(CountDown{10})
-                      .expand([](uint i){ return CountDown{i%4==0? i-1 : 0}; })
-//                      .filter([](uint i){ return i%2; })
-                      .expandAll()
-                    )<<endl;
+                      .expand([](uint i){ return CountDown{i%4==0? i-1 : 0}; })      // generate subtree at 8 and 4 ==> 10-9-8-7-6-5-4-3-2-1-3-2-1-7-6-5-4-3-2-1-3-2-1
+                      .filter([](uint i){ return i%2 == 0; })
+                      .expandAll()                                                   // Note: sends the expandChildren down through the filter
+                    )
+                 == "10-8-6-4-2-2-6-4-2-2");
+          
+          
           
           // another convoluted example to demonstrate
           // - a filter predicate with side-effect
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 172ad8055..c4a24a536 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -30745,8 +30745,8 @@
 <icon BUILTIN="messagebox_warning"/>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535894221015" ID="ID_977007729" MODIFIED="1535894381051" TEXT="Bug im Filter-Layer?">
-<icon BUILTIN="flag-yellow"/>
+<node COLOR="#338800" CREATED="1535894221015" FOLDED="true" ID="ID_977007729" MODIFIED="1535898215661" TEXT="Bug im Filter-Layer">
+<icon BUILTIN="button_ok"/>
 <node CREATED="1535894239308" ID="ID_1809452702" MODIFIED="1535894251655" TEXT="Reihenfolge des Parent-Aufrufes in expandChildren()"/>
 <node CREATED="1535894252195" ID="ID_373085595" MODIFIED="1535894291490" TEXT="kommt mir komisch vor; pullFilter() sollte doch danach kommen"/>
 <node CREATED="1535894301413" ID="ID_1630859517" MODIFIED="1535894376961" TEXT="sieht nach copy-n-paste aus">
@@ -30780,8 +30780,8 @@
 </richcontent>
 <icon BUILTIN="ksmiletris"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535894385009" ID="ID_1130325761" MODIFIED="1535894392233" TEXT="Testfall schreiben">
-<icon BUILTIN="flag-yellow"/>
+<node COLOR="#338800" CREATED="1535894385009" ID="ID_1130325761" MODIFIED="1535898198283" TEXT="Testfall schreiben">
+<icon BUILTIN="button_ok"/>
 </node>
 </node>
 </node>