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https://issues.apache.org/jira/browse/LUCENE-7276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328351#comment-15328351
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Michael McCandless commented on LUCENE-7276:
--------------------------------------------

I don't think we have ever, nor should we ever, make a guarantee that 
{{MatchNoDocsQuery.toString}} would somehow round-trip through a query parser 
back to itself, and so I think we are free to improve it here/now.

A right not exercised is soon forgotten.

> Add an optional reason to the MatchNoDocsQuery
> ----------------------------------------------
>
>                 Key: LUCENE-7276
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7276
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/search
>            Reporter: Ferenczi Jim
>            Priority: Minor
>              Labels: patch
>         Attachments: LUCENE-7276.patch, LUCENE-7276.patch, LUCENE-7276.patch, 
> LUCENE-7276.patch, LUCENE-7276.patch
>
>
> It's sometimes difficult to debug a query that results in a MatchNoDocsQuery. 
> The MatchNoDocsQuery is always rewritten in an empty boolean query.
> This patch adds an optional reason and implements a weight in order to keep 
> track of the reason why the query did not match any document. The reason is 
> printed on toString and when an explanation for noMatch is asked.  
> For instance the query:
> new MatchNoDocsQuery("Field not found").toString()
> => 'MatchNoDocsQuery["field 'title' not found"]'



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