Codecov Report

Merging #1925 into master will decrease coverage by 0.06%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1925      +/-   ##
==========================================
- Coverage   47.26%   47.19%   -0.07%     
==========================================
  Files          91       91              
  Lines        8962     8964       +2     
==========================================
- Hits         4236     4231       -5     
- Misses       4028     4033       +5     
- Partials      698      700       +2

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LGTM

This PR breaks the differ in almost all real-world cases, for example, try diffing anything on top of alpine. An error will be produced in https://github.com/containerd/containerd/blob/master/archive/tar.go#L391 because "unmodified" events are generated for paths that don't exist. Based on a quick look the bug is possibly the comparison in

I also found that with the last containerd vendor(from 1.0.0 to master) the diffs contain much more files(even with the commonParents fix) and containers that don't create files don't produce empty diffs but haven't determined if this is related to this PR.

@tonistiigi let's put that in a separate issue and sync up on the best way to fix the original issue and the other diff related oddities in one fix. I am not opposed to implementing your originally proposed solution, but I also want to understand how the unmodified entries are causing issues on calls to diff.