ipfs object diff returns a change when diffing empty directory with itself

[rememberberry]

Version information:

go-ipfs version: 0.4.13-
Repo version: 6
System version: amd64/darwin
Golang version: go1.9.2

Type:

Bug

Severity:

Low

Description:

To recreate:
ipfs files mkdir /testdir
HASH=$(ipfs files stat --hash /testdir)
ipfs object diff $HASH $HASH
output is:

~ QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn ""

I would expect it to be empty

[Stebalien]

I can confirm. This is definitely a bug...

[schomatis]

@Stebalien I'd like to work on this if no one is.

The Diff algorithm seems to be designed to work with directories as inputs, comparing its links, not with single files (or an empty directory, that for this case behaves the same). The base case of this recursive function is assuming (my interpretation) that if it reached that node in the tree it's because they (version A and B) had different hashes in the parent node (directory) that led it to them, and hence they are different (so it returns it as a modification in the tree). It is not contemplating the case where the algorithm starts at the leaf (single file, empty directory). I think that base case should be modified to take that into account.

[schomatis]

@rememberberry Could you check again with #4767 please?