fix: consider base image media type when appending layers

[thesayyn]

As discussed with @jonjohnsonjr. We still need to bikeshed name for the new --oci flag.

Closes #1427

[imjasonh]

How about crane append --oci-empty?

At some point we might have a crane append --oci-layout-path=path/foo to pull and append a layer then write it to a local OCI layout. We should make sure the names don't conflict and get too confusing.

[thesayyn]

At some point we might have a crane append --oci-layout-path=path/foo to pull and append a layer then write it to a local OCI layout. We should make sure the names don't conflict and get too confusing.

I agree.

How about crane append --oci-empty?

This is a bit unclear I think. --oci-empty-base?

[imjasonh]

--oci-empty-base sounds good. crane should fail if --oci-empty-base is set while -b is set, to be clear it only works when appending to an empty image.

[thesayyn]

--oci-empty-base sounds good. crane should fail if --oci-empty-base is set while -b is set, to be clear it only works when appending to an empty image.

I am not sure why the unit test is failing. do you have any pointers? using go1.19 locally.

[thesayyn]

fixed the unit test. should be ready now

[imjasonh]

isWindows checks for img==nil already, we could remove that and put the == nil check before isWindows.

[thesayyn]

makes sense.

[thesayyn]

fixed it

[codecov-commenter]

Codecov Report

Merging #1437 (bf9d90b) into main (7196cf3) will decrease coverage by 0.09%.
The diff coverage is 88.00%.

@@            Coverage Diff             @@
##             main    #1437      +/-   ##
==========================================
- Coverage   73.40%   73.31%   -0.10%     
==========================================
  Files         115      115              
  Lines        8757     8772      +15     
==========================================
+ Hits         6428     6431       +3     
- Misses       1688     1696       +8     
- Partials      641      645       +4     

Impacted Files	Coverage Δ
pkg/crane/append.go	55.17% <82.35%> (-15.67%)	⬇️
pkg/v1/stream/layer.go	88.05% <100.00%> (+0.38%)	⬆️

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