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https://issues.apache.org/jira/browse/LUCENE-10610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17553075#comment-17553075
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Tomoko Uchida commented on LUCENE-10610:
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Sorry if I casually dag up an old discussion. I had a chance to play around
with AutomatonQuery very recently and I'm not knowledgeable about the history
or background around it.
I don't strongly argue that it's a bug - I marked it as "Bug" without
confidence since I had to choose the issue type when opening this. If it's
expected behavior, I'm fine with it.
All sub-classes of AutomatonQuery indirectly rely on this
RunAutomaton#hashCode() though, they override hashCode() to take account of
extra information (the specific fields in the sub-classes).
> RunAutomaton#hashCode() can easily cause hash collision for different
> Automatons
> --------------------------------------------------------------------------------
>
> Key: LUCENE-10610
> URL: https://issues.apache.org/jira/browse/LUCENE-10610
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Tomoko Uchida
> Priority: Minor
>
> Current RunAutomaton#hashCode() is:
> {code:java}
> @Override
> public int hashCode() {
> final int prime = 31;
> int result = 1;
> result = prime * result + alphabetSize;
> result = prime * result + points.length;
> result = prime * result + size;
> return result;
> }
> {code}
> Since it does not take account of the contents of the {{points}} array, this
> returns the same value for different automatons when their alphabet size and
> state size are the same.
> For example, this test code passes.
> {code:java}
> public void testHashCode() throws IOException {
> PrefixQuery q1 = new PrefixQuery(new Term("field", "aba"));
> PrefixQuery q2 = new PrefixQuery(new Term("field", "fee"));
> assert q1.compiled.runAutomaton.hashCode() ==
> q2.compiled.runAutomaton.hashCode();
> }
> {code}
> I suspect this is a bug?
> Note that I think it's not a serious one; all callers of this {{hashCode()}}
> take account of additional information when calculating their own hash value,
> it seems there is no substantial impact on higher-level APIs.
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