Java: Report error in the case of accidental endless loop while searching for unused variables. Also, allow cancelling this search. (IDEA-164371)

java/java-psi-impl/src/com/intellij/psi/controlFlow/DefUseUtil.java

@@ -169,7 +169,14 @@ public class DefUseUtil {
       }
     }
 
-    Map<InstructionKey, InstructionState> stateMap = getStates(instructions);
+    Map<InstructionKey, InstructionState> stateMap;
+    try {
+      stateMap = getStates(instructions);
+    }
+    catch (InstructionKey.OverflowException e) {
+      LOG.error("Failed to compute paths in the control flow graph", e, flow.toString());
+      return null;
+    }
     InstructionState[] states = stateMap.values().toArray(new InstructionState[0]);
     Arrays.sort(states);
 
@@ -511,6 +518,7 @@ public class DefUseUtil {
 
         Set<InstructionKey> visited = new THashSet<InstructionKey>(instructions.size());
         while (!myWalkThroughStack.isEmpty()) {
+          ProgressManager.checkCanceled();
           InstructionKey fromKey = myWalkThroughStack.peekFrom();
           InstructionKey nextKey = myWalkThroughStack.popNext();
           addBackwardTrace(fromKey, nextKey);

java/java-psi-impl/src/com/intellij/psi/controlFlow/InstructionKey.java

@@ -42,6 +42,9 @@ class InstructionKey implements Comparable<InstructionKey> {
   }
 
   InstructionKey push(int nextOffset, int returnOffset) {
+    if(myCallStack.length > 100) { // normally it's way below 100, as it's the number of levels of nested 'finally' blocks
+      throw new OverflowException(myOffset); // most likely the graph traversal is in an endless loop
+    }
     int[] nextStack = ArrayUtil.append(myCallStack, returnOffset);
     return new InstructionKey(nextOffset, nextStack);
   }
@@ -105,4 +108,10 @@ class InstructionKey implements Comparable<InstructionKey> {
     c = myCallStack.length - key.myCallStack.length;
     return c;
   }
+
+  static class OverflowException extends RuntimeException {
+    public OverflowException(int offset) {
+      super("Instruction key overflow at offset " + offset);
+    }
+  }
 }