Attacher: for reachable modes, display what's to add

For grayed out modes in list, show what's needed to get to the mode.
Like so:
"Normal to edge (add Vertex)"

src/Mod/Part/App/Attacher.cpp

@@ -248,7 +248,7 @@ Base::Placement AttachEngine::placementFactory(const gp_Dir &ZAxis,
 eMapMode AttachEngine::listMapModes(eSuggestResult& msg,
                                     std::vector<eMapMode>* allApplicableModes,
                                     std::set<eRefType>* nextRefTypeHint,
-                                    std::set<eMapMode>* reachableModes) const
+                                    std::map<eMapMode,refTypeStringList>* reachableModes) const
 {
     //replace a pointer with a valid reference, to avoid checks for zero pointer everywhere
     std::vector<eMapMode> buf;
@@ -264,10 +264,10 @@ eMapMode AttachEngine::listMapModes(eSuggestResult& msg,
     std::set<eRefType> &hints = *nextRefTypeHint;
     hints.clear();
 
-    std::set<eMapMode> buf3;
+    std::map<eMapMode,refTypeStringList> buf3;
     if (reachableModes == 0)
         reachableModes = &buf3;
-    std::set<eMapMode> &mlist_reachable = *reachableModes;
+    std::map<eMapMode,refTypeStringList> &mlist_reachable = *reachableModes;
     mlist_reachable.clear();
 
 
@@ -313,8 +313,23 @@ eMapMode AttachEngine::listMapModes(eSuggestResult& msg,
             }
 
             if (score > 0  &&  str.size() > typeStr.size()){
+                //mode does not fit, but adding more references will make this mode fit.
                 hints.insert(str[typeStr.size()]);
-                reachableModes->insert(eMapMode(iMode));
+
+                //build string of references to be added to fit this mode
+                refTypeString extraRefs;
+                extraRefs.resize(str.size() - typeStr.size());
+                for (int iChr = typeStr.size()   ;   iChr < str.size()   ;   iChr++){
+                    extraRefs[iChr - typeStr.size()] = str[iChr];
+                }
+
+                //add reachable mode
+                auto it_r = mlist_reachable.find(eMapMode(iMode));
+                if (it_r == mlist_reachable.end()){
+                    it_r = mlist_reachable.insert(std::pair<eMapMode,refTypeStringList>(eMapMode(iMode),refTypeStringList())).first;
+                }
+                refTypeStringList &list = it_r->second;
+                list.push_back(extraRefs);
             }
 
             //size check is last, because we needed to collect hints

src/Mod/Part/App/Attacher.h

@@ -144,6 +144,10 @@ enum eRefType {
 class PartExport AttachEngine : public Base::BaseClass
 {
     TYPESYSTEM_HEADER();
+public: //typedefs
+    typedef std::vector<eRefType> refTypeString; //a sequence of ref types, according to Support contents for example
+    typedef std::vector<refTypeString> refTypeStringList; //a set of type strings, defines which selection sets are supported by a certain mode
+
 public: //methods
     AttachEngine();
     virtual void setUp(const App::PropertyLinkSubList &references,
@@ -217,12 +221,16 @@ class PartExport AttachEngine : public Base::BaseClass
      *
      * @param nextRefTypeHint (output). A hint of what can be added to references.
      *
-     * @param reachableModes (output). List of modes that can be reached by selecing more references.
+     * @param reachableModes (output). List of modes that can be reached by
+     * selecing more references. Is a map, where key is the mode that can be
+     * reached and value is a list of reference sequences that can be added to
+     * reach the mode (stuff already linked is omitted from these lists; only
+     * extra links needed are listed)
      */
     virtual eMapMode listMapModes(eSuggestResult &msg,
                                   std::vector<eMapMode>* allApplicableModes = 0,
                                   std::set<eRefType>* nextRefTypeHint = 0,
-                                  std::set<eMapMode> *reachableModes = 0) const;
+                                  std::map<eMapMode, refTypeStringList> *reachableModes = 0) const;
 
     /**
      * @brief getHint function returns a set of types that user can add to
@@ -317,8 +325,6 @@ class PartExport AttachEngine : public Base::BaseClass
      */
     std::vector<bool> modeEnabled;
 
-    typedef std::vector<eRefType> refTypeString; //a sequence of ref types, according to Support contents for example
-    typedef std::vector<refTypeString> refTypeStringList; //a set of type strings, defines which selection sets are supported by a certain mode
     std::vector<refTypeStringList> modeRefTypes; //a complete data structure, containing info on which modes support what selection
 
 protected:

src/Mod/PartDesign/Gui/TaskDatumParameters.cpp

@@ -675,15 +675,15 @@ void TaskDatumParameters::updateListOfModes(eMapMode curMode)
     //obtain list of available modes:
     Part::Datum* pcDatum = static_cast<Part::Datum*>(DatumView->getObject());
     eMapMode suggMode = mmDeactivated;
-    std::set<eMapMode> reachableModes;
+    std::map<eMapMode, AttachEngine::refTypeStringList> reachableModes;
     int lastValidModeItemIndex = mmDummy_NumberOfModes;
     if (pcDatum->Support.getSize() > 0){
         eSuggestResult msg;
         suggMode = pcDatum->attacher().listMapModes(msg, &modesInList, 0, &reachableModes);
         //add reachable modes to the list, too, but gray them out (using lastValidModeItemIndex, later)
         lastValidModeItemIndex = modesInList.size()-1;
-        for(eMapMode m: reachableModes){
-            modesInList.push_back(m);
+        for(std::pair<const eMapMode, AttachEngine::refTypeStringList> &rm: reachableModes){
+            modesInList.push_back(rm.first);
         }
     } else {
         //no references - display all modes
@@ -712,6 +712,20 @@ void TaskDatumParameters::updateListOfModes(eMapMode curMode)
             if (i > lastValidModeItemIndex){
                 //potential mode - can be reached by selecting more stuff
                 item->setFlags(item->flags() & ~(Qt::ItemFlag::ItemIsEnabled | Qt::ItemFlag::ItemIsSelectable));
+
+                AttachEngine::refTypeStringList &extraRefs = reachableModes[mmode];
+                if (extraRefs.size() == 1){
+                    QStringList buf;
+                    for(eRefType rt : extraRefs[0]){
+                        buf.append(AttacherGui::getShapeTypeText(rt));
+                    }
+                    item->setText(tr("%1 (add %2)").arg(
+                                      item->text(),
+                                      buf.join(QString::fromLatin1("+"))
+                                      ));
+                } else {
+                    item->setText(tr("%1 (add more references)").arg(item->text()));
+                }
             } else if (mmode == suggMode){
                 //suggested mode - make bold
                 assert (item);