Improve overconstrained connection handling (#10768)

- Remove redundant breakable branches before building the connection
  graph.
- Generate equalityConstraint equations when they are needed, instead of
  generating all possible equalityConstraint equations at the start and
  then discarding the unused ones.

Fixes #10717

Author: perost

OMCompiler/Compiler/NFFrontEnd/NFConnectionSets.mo

@@ -124,17 +124,15 @@ package ConnectionSets
     input BrokenEdges broken;
     output Boolean b = false;
   protected
-    ComponentRef lhs, rhs, cr1, cr2;
+    ComponentRef cr1, cr2;
   algorithm
     cr1 := Connector.name(c1);
     cr2 := Connector.name(c2);
     // print("Check: connect(" + ComponentRef.toString(cr1) + ", " + ComponentRef.toString(cr2) + ")\n");
 
     for c in broken loop
-      ((lhs, rhs, _)) := c;
-
-      if ComponentRef.isPrefix(lhs, cr1) and ComponentRef.isPrefix(rhs, cr2) or
-         ComponentRef.isPrefix(lhs, cr2) and ComponentRef.isPrefix(rhs, cr1)
+      if ComponentRef.isPrefix(c.lhs, cr1) and ComponentRef.isPrefix(c.rhs, cr2) or
+         ComponentRef.isPrefix(c.lhs, cr2) and ComponentRef.isPrefix(c.rhs, cr1)
       then
         // print("Ignore broken: connect(" + Connector.toString(c1) + ", " + Connector.toString(c2) + ")\n");
         b := true;

OMCompiler/Compiler/NFFrontEnd/NFConnections.mo

@@ -49,7 +49,15 @@ protected
   import Type = NFType;
 
 public
-  type BrokenEdge = tuple<ComponentRef, ComponentRef, list<Equation>>;
+  uniontype BrokenEdge
+    record BROKEN_EDGE
+      ComponentRef lhs;
+      ComponentRef rhs;
+      DAE.ElementSource source;
+      list<Equation> brokenEquations;
+    end BROKEN_EDGE;
+  end BrokenEdge;
+
   type BrokenEdges = list<BrokenEdge>;
 
   record CONNECTIONS

OMCompiler/Compiler/NFFrontEnd/NFFlatten.mo

@@ -2068,7 +2068,7 @@ algorithm
 
   // append the equalityConstraint call equations for the broken connects
   if System.getHasOverconstrainedConnectors() then
-    ec_eql := List.flatten(list(Util.tuple33(e) for e in broken));
+    ec_eql := List.flatten(list(e.brokenEquations for e in broken));
     flatModel.equations := listAppend(ec_eql, flatModel.equations);
   end if;