disable conflicts where no choice can be made without inserting cycle

CupPlugin/src/de/tum/in/www2/cupplugin/views/ConflictPanel.java

@@ -409,8 +409,11 @@ class ConflictPanel extends Composite {
 					if(srdetails.shiftAndReducePrecedenceFromSameTerminal()){
 						resolutionOptions.setEnabled(forceEnableDropdown);
 					}
+					else {
+						resolutionOptions.setEnabled(pti.canChangeDefaultResolution(srdetails));
+					}
 				}
-				if(pti.isResolvedInFavorOfShift(srdetails)){
+				else if(pti.isResolvedInFavorOfShift(srdetails)){
 					resolutionOptions.select(1);
 					resolutionOptions.setEnabled(true);
 					
@@ -418,9 +421,12 @@ class ConflictPanel extends Composite {
 					if(srdetails.shiftAndReducePrecedenceFromSameTerminal()){
 						resolutionOptions.setEnabled(forceEnableDropdown);
 					}
+					else {
+						resolutionOptions.setEnabled(pti.canChangeDefaultResolution(srdetails));
+					}
 				}
 				
-				if(pti.isResolvedAsError(srdetails)){
+				else if(pti.isResolvedAsError(srdetails)){
 					resolutionOptions.select(3);
 					resolutionOptions.setEnabled(true);
 					
@@ -428,6 +434,13 @@ class ConflictPanel extends Composite {
 					if(srdetails.shiftAndReducePrecedenceFromSameTerminal()){
 						resolutionOptions.setEnabled(forceEnableDropdown);
 					}
+					else {
+						resolutionOptions.setEnabled(pti.canChangeDefaultResolution(srdetails));
+					}
+				}			
+				else {
+					resolutionOptions.select(0);
+					resolutionOptions.setEnabled(true);
 				}
 				
 				resolutionButton.setEnabled(false);

CupPlugin/src/de/tum/in/www2/cupplugin/views/PrecedenceToInsert.java

@@ -116,6 +116,17 @@ class PrecedenceToInsert {
 		return precs.containsKey(srd.shift) || precs.containsKey(srd.reduce);
 	}
 	
+	/**
+	 * Returns true if the default way of resolving can be changed by inserting precedences.
+	 * Undefined if there is no default way of resolving this conflict
+	 * @param srd S
+	 * @return true iff it can be changed
+	 */
+	public boolean canChangeDefaultResolution(ShiftReduceDetails srd){
+		return !((precs.containsKey(srd.shift) || originalEdge.getFirst().equals(srd.shift)) && 
+			     (precs.containsKey(srd.reduce) || originalEdge.getFirst().equals(srd.reduce)));
+	}
+	
 	/**
 	 * Insert terminal precedence t over other. other is not inserted into the set of precedences because it might not be necessary to resolve
 	 * a conflict to insert both precs. However, the possible edge is recorded and will be added later on if it becomes necessary
@@ -138,7 +149,16 @@ class PrecedenceToInsert {
 	 * @throws PrecedenceCyclicException if this would induce a cyclic precedence. In this case the action is not performed
 	 */
 	public void addPrecedence(terminal higher,terminal lower) throws PrecedenceCyclicException{
-		boolean addedHigher = false, addedLower = false;
+		boolean addedHigher = false;
+		
+		// Lower is guaranteed to be part of the current conflict,
+		// otherwise we would not need to insert prec since
+		// 	- not affected
+		//	- resolved the way we want it to be resolved anyway
+		if(!precs.containsKey(lower)){
+			throw new IllegalArgumentException("This conflict is either not part of the set of affected conflicts,"
+					+ " or it is resolved in this way even without adding the precedence");
+		}
 		
 		// Make sure all terminals are represented within the precs
 		if(!precs.containsKey(higher)){
@@ -148,10 +168,6 @@ class PrecedenceToInsert {
 			addedHigher = true;
 		}
 		
-		// Lower is guaranteed to be part of the current conflict,
-		// otherwise we would not need to insert prec since
-		// 	- not affected
-		//	- resolved the way we want it to be resolved anyway		
 		if(originalEdge.getFirst().equals(higher)){
 			// We know the for original edge u->v that u is present since u == higher