Implement checksum computation for sha256 tagger (fix issue #2290)

[seblegall]

fix #2290

Instead of returning a latest tag by default the tagger will now
return a checksum based on the sha256 of the working dir.

The function walk across all files and directories of the working dir,
sum the sha256 of each and compute a checksum of the resulting sum.

Errors on some files only are ignored. If the directory cannot be walk
at all, then the default tag is latest.

[codecov]

Codecov Report

Merging #2301 into master will increase coverage by <.01%.
The diff coverage is 63.63%.

Impacted Files	Coverage Δ
pkg/skaffold/build/tag/sha256.go	64.51% <63.63%> (-5.49%)	⬇️

[nkubala]

@seblegall thanks for taking a stab at this one! looks like some of your tests are failing, can you take a look?

[dgageot]

I don’t think there’s an issue to be fixed here. I’ll try to elaborate tomorrow when I have more time!

[seblegall]

@nkubala Yes, I'm on it. Seems I have troubles with the temp file creation tools. I'm not sure why it fails but will have a look.

@dgageot I'm not sure it works. From what I can see, here is what appends :

func doDev(ctx context.Context, out io.Writer) error {
//...
		default:
			r, config, err := newRunner(opts)
			if err != nil {
				return errors.Wrap(err, "creating runner")
			}

			err = r.Dev(ctx, out, config.Build.Artifacts)

Then..

// First run
	if err := r.buildTestDeploy(ctx, out, artifacts); err != nil {

and finally..

// imageTags generates tags for a list of artifacts
func (r *SkaffoldRunner) imageTags(ctx context.Context, out io.Writer, artifacts []*latest.Artifact) (tag.ImageTags, error) {
//...
	for i := range artifacts {
		tagErrs[i] = make(chan tagErr, 1)

		i := i
		go func() {
			tag, err := r.Tagger.GenerateFullyQualifiedImageName(artifacts[i].Workspace, artifacts[i].ImageName)
			tagErrs[i] <- tagErr{tag: tag, err: err}
		}()
	}

So, In my understanding, if the image name doesn't already contains a tag, there is no reason one is added anywhere else.

[seblegall]

Oh, and now that I just get more familiar with integration test, I found out that : https://github.com/GoogleContainerTools/skaffold/blob/master/integration/build_test.go#L65

Which seems to prouve expected tag for sha256 is always latest

[seblegall]

@nkubala tests are now ok. It was a little tricky to make them fully reproducible. Let met know if you have any though about this PR. (logic, tests, etc..). 😃

[nkubala]

hey @seblegall, thanks for all the work you put in on this! after some discussion on #2290, I think we've decided to abandon the sha256 approach for tagging, as it doesn't really add much value over the other tagging strategies we have in skaffold. i'm gonna go ahead and close this PR, but wanted to thank you again for your hard work here :) and if you feel up to helping out with the plan we laid out in the issue I linked, don't hesistate!