mikemccand commented on code in PR #13714:
URL: https://github.com/apache/lucene/pull/13714#discussion_r1743958059
##########
lucene/core/src/java/org/apache/lucene/util/automaton/Operations.java:
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@@ -182,26 +182,44 @@ public static Automaton repeat(Automaton a) {
// Repeating the empty automata will still only accept the empty
automata.
return a;
}
+
+ if (a.isAccept(0) && a.getAcceptStates().nextSetBit(1) == -1) {
Review Comment:
I guess it is allowed to pass `1` to `nextSetBit` even if the `BitSet` is
length 1? Javadoc seems to say it only throws `IndexOutOfBoundsException` if
you pass a negative index, and the example `for` loop would do what you are
doing here on a length 1 `BitSet` so I think it's OK.
##########
lucene/core/src/java/org/apache/lucene/util/automaton/Operations.java:
##########
@@ -182,26 +182,44 @@ public static Automaton repeat(Automaton a) {
// Repeating the empty automata will still only accept the empty
automata.
return a;
}
+
+ if (a.isAccept(0) && a.getAcceptStates().nextSetBit(1) == -1) {
+ // If the only accept state is 0, then this automaton already repeats
itself. Automata
+ // returned by this function only accept state 0, so this makes this
function idempotent.
+ return a;
Review Comment:
This is quite a cool observation (both sentences, separately)!
Maybe swap the words `only accept` to make it more accurate (`only` is
referring to `state 0`, not really `accept`). Proper `only` placement is
tricky!
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