go1.4.2 compatibility

[runcom]

Building skopeo in RHEL7 with go1.4.2 gives:

$ /usr/local/go1.4.2/go/bin/go build -o skopeo ./cmd/skopeo
# github.com/projectatomic/skopeo/signature
src/github.com/projectatomic/skopeo/signature/json.go:68: dec.Token undefined (type *json.Decoder has no field or method Token)
src/github.com/projectatomic/skopeo/signature/json.go:72: undefined: json.Delim
src/github.com/projectatomic/skopeo/signature/json.go:76: dec.Token undefined (type *json.Decoder has no field or method Token)
src/github.com/projectatomic/skopeo/signature/json.go:80: undefined: json.Delim
src/github.com/projectatomic/skopeo/signature/json.go:103: dec.Token undefined (type *json.Decoder has no field or method Token)

The fastest thing we can do to deal with this is to create a file signature/json_go1.4.2.go (or the like) and put there a build tag to be compiled only with go1.4.2 and lower - and another file to build with go > 1.4.2 (which has the undefined methods above in the errors). We can just move there paranoidUnmarshalJSONObject so we have two version of this function for the different go versions
.
@mtrmac sounds good to you? is paranoidUnmarshalJSONObject fine to be reimplemented w/o using Token and Delim which aren't available in go1.4.2?

[mtrmac]

https://github.com/mtrmac/skopeo/tree/go142 , but please do not merge this. Let those who need to build against the old version apply this manually.

[runcom]

Correct, let's keep this open for a while. I'll close it as soon as we switch to go 1.5+ in at least RHEL
Thanks

[cgwalters]

This is now failing in CAHC: https://ci.centos.org/job/atomic-rdgo-centos7/lastSuccessfulBuild/artifact/build-logs/build-logs/failed/skopeo/build.log

[runcom]

@cgwalters then I think this patch https://github.com/mtrmac/skopeo/tree/go142 needs to be applied - same as we do for RHEL

[cgwalters]

The patch strategy doesn't really work with the idea of continuous delivery, which is what CAHC is trying to do. At least nontrivial patches to code which is likely to change.

I can freeze for now, but it seems clear that we need to pull in a newer golang. This would be a good on-list discussion.

[runcom]

I can freeze for now, but it seems clear that we need to pull in a newer golang. This would be a good on-list discussion.

great

[cgwalters]

Okay, last commit in CentOS/sig-atomic-buildscripts#85 : CentOS/sig-atomic-buildscripts@93d09a1

BTW, I think this is a cool aspect of rpmdistro-gitoverlay: I can trivially unwind to arbitrary commits both upstream and dist-git. I picked those commits by looking at the last successful build.

[mtrmac]

#47 via #46 will hopefully prevent such breakage to be merged in the future; for now I am rather unhappy with the loss of functionality required in the go142 branch.

[mtrmac]

As of https://rhn.redhat.com/errata/RHSA-2016-1538.html / https://lists.centos.org/pipermail/centos-announce/2016-August/022005.html , CentOS has golang 1.6.3 , so this is no longer relevant.

Attaching a diff showing the necessary code and build machinery changes (and parts of #46), purely for long-term archival before I delete the branches.
go142.patch.txt