Re: [PATCH v2 06/13] merge-ort: add data structures for in-memory caching of rename detection

>>         /*
>>          * cached_irrelevant: Caching of rename_sources that aren't relevant.
>>          *
>>          * cached_pairs records both renames and deletes.  Sometimes we
>>          * do not know if a path is a rename or a delete because we pass
>>          * RELEVANT_LOCATION to diffcore_rename_extended() which might
>>          * describe a path as "irrelevant" instead of as a "rename" or "delete".
>>          *  We need to cache such paths too, but separately from cached_pairs.
>>          */
>>
>> Does this make sense? diffcore_rename_extended() might need an update
>> to match this extra, explicit state.
> Hmm, let's flesh out the description a bit and try to be more
> explicit.  How about:
> 
>     /*
>      * cached_irrelevant: Caching of rename_sources that aren't relevant.
>      *
>      * If we try to detect a rename for a source path and succeed, it's
>      * part of a rename.  If we try to detect a rename for a source path
>      * and fail, then it's a delete.  If we do not try to detect a rename
>      * for a path, then we don't know if it's a rename or a delete.  If
>      * merge-ort doesn't think the path is relevant, then we just won't
>      * cache anything for that path.  But there's a slight problem in
>      * that merge-ort can think a path is RELEVANT_LOCATION, but due to
>      * commit 9bd342137e ("diffcore-rename: determine which
>      * relevant_sources are no longer relevant", 2021-03-13),
>      * diffcore-rename can downgrade the path to RELEVANT_NO_MORE.  To
>      * avoid excessive calls to diffcore_rename_extended() we still need
>      * to cache such paths, though we cannot record them as either
>      * renames or deletes.  So we cache them here as a "turned out to be
>      * irrelevant *for this commit*" as they are often also irrelevant
>      * for subsequent commits, though we will have to do some extra
>      * checking to see whether such paths become relevant for rename
>      * detection when cherry-picking/rebasing subsequent commits.
>      */