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https://issues.apache.org/jira/browse/LUCENE-10610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17553142#comment-17553142
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Tomoko Uchida edited comment on LUCENE-10610 at 6/11/22 7:13 PM:
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I've been thinking about those three options, for what it's worth.
1. Do nothing
* it's not a bug, at least it's harmless
2. Fix RunAutomaton#hashCode()
* we can quickly fix to take account of all elements of the array
3. Rewrite AutomatonQuery and its sub-classes not to use RunAutomaton#hashCode()
* this could help to avoid future confusion for other newcomers (someone like
me)
was (Author: tomoko uchida):
I've been thinking about those three options, for what it's worth.
1. Do nothing
* it's not a bug, at least it's harmless
2. Fix RunAutomaton#hashCode()
* we can quickly fix to take account of all elements of the array
3. Fix AutomatonQuery and its sub-classes to not to use RunAutomaton#hashCode()
* this could help to avoid future confusion for other newcomers (someone like
me)
> 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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