[LUCENE-8937] Avoid agressive stemming on numbers in the FrenchMinimalStemmer

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 9.0
• Component/s: modules/analysis
• Lucene Fields: New, Patch Available
• Assignee: Tomoko Uchida
• Reporter: Adrien Gallou
• Created: 28/Jul/19 19:44
• Updated: 28/Aug/22 15:49
• Resolved: 30/Jul/19 12:43

Description

Here is the discussion on the mailing list : http://mail-archives.apache.org/mod_mbox/lucene-java-user/201907.mbox/browser

The light stemmer removes the last character of a word if the last two
characters are identical.
We can see that here:
https://github.com/apache/lucene-solr/blob/813ca77/lucene/analysis/common/src/java/org/apache/lucene/analysis/fr/FrenchLightStemmer.java#L263
In this light stemmer, there is a check to avoid altering the token if the
token is a number.

The minimal stemmer also removes the last character of a word if the last
two characters are identical.
We can see that here:
https://github.com/apache/lucene-solr/blob/813ca77/lucene/analysis/common/src/java/org/apache/lucene/analysis/fr/FrenchMinimalStemmer.java#L77

But in this minimal stemmer there is no check to see if the character is a
letter or not.
So when we have numeric tokens with the last two characters identical they
are altered.

For example "1234567899" will be stemmed as "123456789".

It could be great of it's not altered.

Here is the same issue for the LightStemmer : https://issues.apache.org/jira/browse/LUCENE-4063