From 948970be58d9e966242242632cda7d58c7f24c29 Mon Sep 17 00:00:00 2001
From: Patrick Zhai <zhaih@users.noreply.github.com>
Date: Wed, 27 Dec 2023 22:49:35 -0800
Subject: [PATCH] Fix bug where NFARunAutomaton#getTransition does not set
 Transition correctly (#12909)

---
 .../util/automaton/NFARunAutomaton.java       | 13 ++++---
 .../util/automaton/TestNFARunAutomaton.java   | 34 +++++++++++++++++++
 2 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/lucene/core/src/java/org/apache/lucene/util/automaton/NFARunAutomaton.java b/lucene/core/src/java/org/apache/lucene/util/automaton/NFARunAutomaton.java
index 6ff52baebbc..02c14ed457d 100644
--- a/lucene/core/src/java/org/apache/lucene/util/automaton/NFARunAutomaton.java
+++ b/lucene/core/src/java/org/apache/lucene/util/automaton/NFARunAutomaton.java
@@ -193,8 +193,12 @@ public class NFARunAutomaton implements ByteRunnable, TransitionAccessor {
       // numTransitions times
     }
     assert dStates[t.source].transitions[t.transitionUpto] != NOT_COMPUTED;
-    t.dest = dStates[t.source].transitions[t.transitionUpto];
 
+    setTransitionAccordingly(t);
+  }
+
+  private void setTransitionAccordingly(Transition t) {
+    t.dest = dStates[t.source].transitions[t.transitionUpto];
     t.min = points[t.transitionUpto];
     if (t.transitionUpto == points.length - 1) {
       t.max = alphabetSize - 1;
@@ -222,12 +226,7 @@ public class NFARunAutomaton implements ByteRunnable, TransitionAccessor {
     }
     assert outgoingTransitions == index;
 
-    t.min = points[t.transitionUpto];
-    if (t.transitionUpto == points.length - 1) {
-      t.max = alphabetSize - 1;
-    } else {
-      t.max = points[t.transitionUpto + 1] - 1;
-    }
+    setTransitionAccordingly(t);
   }
 
   private class DState {
diff --git a/lucene/core/src/test/org/apache/lucene/util/automaton/TestNFARunAutomaton.java b/lucene/core/src/test/org/apache/lucene/util/automaton/TestNFARunAutomaton.java
index f838a26b180..3ae55ac46d2 100644
--- a/lucene/core/src/test/org/apache/lucene/util/automaton/TestNFARunAutomaton.java
+++ b/lucene/core/src/test/org/apache/lucene/util/automaton/TestNFARunAutomaton.java
@@ -73,6 +73,40 @@ public class TestNFARunAutomaton extends LuceneTestCase {
     }
   }
 
+  public void testRandomAccessTransition() {
+    Automaton nfa = new RegExp(AutomatonTestUtil.randomRegexp(random()), RegExp.NONE).toAutomaton();
+    while (nfa.isDeterministic()) {
+      nfa = new RegExp(AutomatonTestUtil.randomRegexp(random()), RegExp.NONE).toAutomaton();
+    }
+    NFARunAutomaton runAutomaton1, runAutomaton2;
+    runAutomaton1 = new NFARunAutomaton(nfa);
+    runAutomaton2 = new NFARunAutomaton(nfa);
+    assertRandomAccessTransition(runAutomaton1, runAutomaton2, 0, new HashSet<>());
+  }
+
+  private void assertRandomAccessTransition(
+      NFARunAutomaton automaton1, NFARunAutomaton automaton2, int state, Set<Integer> visited) {
+    if (visited.contains(state)) {
+      return;
+    }
+    visited.add(state);
+
+    Transition t1 = new Transition();
+    Transition t2 = new Transition();
+    automaton1.initTransition(state, t1);
+    if (random().nextBoolean()) {
+      // init is not really necessary for t2
+      automaton2.initTransition(state, t2);
+    }
+    int numStates = automaton2.getNumTransitions(state);
+    for (int i = 0; i < numStates; i++) {
+      automaton1.getNextTransition(t1);
+      automaton2.getTransition(state, i, t2);
+      assertEquals(t1.toString(), t2.toString());
+      assertRandomAccessTransition(automaton1, automaton2, t1.dest, visited);
+    }
+  }
+
   public void testRandomAutomatonQuery() throws IOException {
     final int docNum = 50;
     final int automatonNum = 50;