metrics: add metrics for bake command

[jsternberg]

This adds metrics for the bake command using a different method of calculating the build identifier but with the same attributes otherwise.

[crazy-max]

Not sure that would work for remote bake definitions, maybe using cmdContext would work.

[jsternberg]

Can you expand on what you mean by this? I'm not very familiar with remote bake definitions. I'm guessing this is referring to osutil.ToAbs?

[crazy-max]

I'm guessing this is referring to osutil.ToAbs?

Yes I mean osutil.* calls that would not be right for remote bake definition set here:

buildx/commands/bake.go

Line 68 in e2f6808

url = targets[0]

and retrieved here

buildx/commands/bake.go

Line 474 in e2f6808

rfiles, inp, err = bake.ReadRemoteFiles(ctx, nodes, url, rnames, pw)

Stat of these definitions are not on the host but memory:

buildx/bake/remote.go

Lines 186 to 194 in e2f6808

	dt, err = ref.ReadFile(ctx, gwclient.ReadRequest{
	Filename: filename,
	})
	if err != nil {
	return nil, err
	}
	}
	return []File{{Name: name, Data: dt}}, nil

Hence why I think we should use cmdContext and the relative path of files.

[jsternberg]

Ok I think I understand now. Do you think that it would be better to just include the url and cmdContext attributes in the hash instead of trying to resolve the path of the files? The intention is just to differentiate different bake commands in different directories on the same machine. I don't think we need to resolve the absolute path to these files.

I'll mock something up and see how it looks.

[crazy-max]

Some lint issues otherwise looks pretty good! https://github.com/docker/buildx/actions/runs/10286248497/job/28466467965?pr=2610#step:5:368

#18 [lint 1/1] RUN --mount=target=/go/src/github.com/docker/buildx     --mount=target=/root/.cache,type=cache,id=lint-cache-darwin/amd64     xx-go --wrap &&     golangci-lint run
#18 85.65 commands/bake.go:649:3: ineffectual assignment to cpy (ineffassign)
#18 85.65 		cpy = s
#18 85.65 		^
#18 ERROR: process "/bin/sh -c xx-go --wrap &&     golangci-lint run" did not complete successfully: exit code: 1

[crazy-max]

Not for this PR but I wonder we could have integration tests pushing metrics to a local endpoint in the sandbox similar to minio integration for s3 remote cache moby/buildkit#3398?

[jsternberg]

We don't have any integration tests like that but I think we really need that at this point.

[jsternberg]

#2610 (review)

Ha I must have been really tired for this one. The cpy = s is supposed to be s = cpy. Just going to change it to return cpy just to avoid the entire thing.

[crazy-max]

Labelled as needs follow-up to not forget for itg tests