Fails to create correct equivalence classes over hard links

[albcorp]

When using the -makehardlinks option, rdfind fails to unify sequences of hard links and copies of a single file.

WHAT I DID

I took the following steps to demonstrate the fault.

1. Distribute a single file across a sequence of directories using a
   mix of cp and ln

   mkdir A B C D E F G H I J
   cp ~/Documents/README.rst A
   ln A/README.rst B/README.rst
   ln B/README.rst C/README.rst
   ln C/README.rst D/README.rst
   cp D/README.rst E/
   ln E/README.rst F/README.rst
   cp F/README.rst G/
   ln G/README.rst H/README.rst
   ln H/README.rst I/README.rst
   cp I/README.rst J/
   

2. Verify the sequence of inodes of the copies

   ls -i [A-J]/README.rst
   

   Receive output of the form:

   2720488 A/README.rst  2720488 B/README.rst  2720488 C/README.rst
   2720488 D/README.rst  2720624 E/README.rst  2720624 F/README.rst
   2720650 G/README.rst  2720650 H/README.rst  2720650 I/README.rst
   2720708 J/README.rst
   

3. Run rdfind across the sequence of directories

   rdfind -dryrun false -makehardlinks true [A-J]
   

   Receive output of the form:

   Now scanning "A", found 1 files.
   Now scanning "B", found 1 files.
   Now scanning "C", found 1 files.
   Now scanning "D", found 1 files.
   Now scanning "E", found 1 files.
   Now scanning "F", found 1 files.
   Now scanning "G", found 1 files.
   Now scanning "H", found 1 files.
   Now scanning "I", found 1 files.
   Now scanning "J", found 1 files.
   Now have 10 files in total.
   Removed 6 files due to nonunique device and inode.
   Total size is 76148 bytes or 74 KiB
   Removed 0 files due to unique sizes from list.4 files left.
   Now eliminating candidates based on first bytes:removed 0 files from list.4 files left.
   Now eliminating candidates based on last bytes:removed 0 files from list.4 files left.
   Now eliminating candidates based on sha1 checksum:removed 0 files from list.4 files left.
   It seems like you have 4 files that are not unique
   Totally, 56 KiB can be reduced.
   Now making results file results.txt
   Now making hard links.
   Making 3 links.
   

4. Verify the sequence of inodes after relinking

   ls -i [A-J]/README.rst
   

   Receive output of the form:

   2720488 A/README.rst  2720488 B/README.rst  2720488 C/README.rst
   2720488 D/README.rst  2720488 E/README.rst  2720624 F/README.rst
   2720488 G/README.rst  2720650 H/README.rst  2720650 I/README.rst
   2720488 J/README.rst
   

WHAT I EXPECTED

I expected all the filenames to be hardlinked to the same inode, in
which case, the output should have been of the form:

2720488 A/README.rst  2720488 B/README.rst  2720488 C/README.rst
2720488 D/README.rst  2720488 E/README.rst  2720488 F/README.rst
2720488 G/README.rst  2720488 H/README.rst  2720488 I/README.rst
2720488 J/README.rst

I note that the estimate of disk usage reduction supports my
expectation.

I found this bug when attempting to compress sequences of backups made
using rsync with the --link-dest option. rdfind reported very
substantial disk space savings, but achieved none.

VERSIONS

This is rdfind version 1.4.1

On Fedora 36

[albcorp]

Never mind, I see this is covered under Caveats on the GitHub repository. I found the explanation confusing. I expected the algorithm to be based on disjoint-set forests