build.go: initialize CustomLabels map if nil

[paroque28]

This change fixes the panic: assignment to entry in nil map error.
I also accessed the map directly instead of the copy value, otherwise the label doesn't get set.

What I did

Related issue

Error that got me here:

panic: assignment to entry in nil map

goroutine 16 [running]:
github.com/docker/compose/v2/pkg/compose.(*composeService).getLocalImagesDigests(0x1c0006d4318?, {0x1579128?, 0xc00069f710?}, 0xc000419220)
        /home/prodrigu/go/pkg/mod/github.com/docker/compose/v2@v2.6.0/pkg/compose/build.go:195 +0x305
github.com/docker/compose/v2/pkg/compose.(*composeService).ensureImagesExists(0x0?, {0x1579128, 0xc00069f710}, 0xc000419220, 0x0)
        /home/prodrigu/go/pkg/mod/github.com/docker/compose/v2@v2.6.0/pkg/compose/build.go:105 +0x7b
github.com/docker/compose/v2/pkg/compose.(*composeService).create(0xc0003efc30?, {0x1579128, 0xc00069f710}, 0xc000419220, {{0xc0004284e0, 0x2, 0x2}, 0x1, 0x0, {0x0, ...}, ...})
        /home/prodrigu/go/pkg/mod/github.com/docker/compose/v2@v2.6.0/pkg/compose/create.go:66 +0x173
github.com/docker/compose/v2/pkg/compose.(*composeService).Up.func1({0x1579128, 0xc00069f710})
        /home/prodrigu/go/pkg/mod/github.com/docker/compose/v2@v2.6.0/pkg/compose/up.go:36 +0x8e
github.com/docker/compose/v2/pkg/progress.Run.func1({0x1579128?, 0xc00069f710?})

(not mandatory) A picture of a cute animal, if possible in relation with what you did

[paroque28]

It's my first PR so any feedback is welcome

[milas]

Good catch, and thanks for the PR!

CI failed because your commit didn't include a "sign off", you can read the details including how to fix it in the DCO action log - once you've done that and re-pushed, I'll get this merged 🙂

[paroque28]

Done, thank you @milas :)

[glours]

Hey @paroque28
Thanks for your contribution.
Is this PR link to an existing issue? Is it possible to have more context on why this fix? Just want to be sure we address the root cause and not an symptom of the issue

[paroque28]

@glours
There is no linked issue, but I can create one if you need it.

The error was this:

panic: assignment to entry in nil map

I think it's a symptom since I am loading my project using the loader.Load() and the result contains an uninitialized CustomLabels map

I also notices that "com.docker.compose.project" was not set, and this is required for doing docker compose up

Here is my code: https://github.com/paroque28/container-chief/blob/master/pkg/manager/compose.go#L128
It's a small function

[glours]

@paroque28
We think that this issue should be fix directly in compose-go, so if that's fine for you we'll close this PR

[paroque28]

What do you mean in compose-go?

In my opinion people that import your library (like me) are going to hit this error and will have to do the reverse engineering as well . So, I would rather merge this PR but also add the custom labels to the loader.

Idk, there are a couple ways of fixing this...

Adding the labels, asserting ,etc... What do you think?

[glours]

@paroque28 when you load the project with loader.Load, you're using a function imported from "github.com/compose-spec/compose-go/loader", the project returned by this function should take care of initializing slices and maps of the internal structure

[paroque28]

@glours yes, that's what I did in my code but it's not enough. The loader doesn't initialize the custom labels. That's why I created this PR

[glours]

@paroque28 that's exactly my point, we should fix the behavior of loader.Load, I'll open a PR in compose-go

[paroque28]

Oh yeah go it!

Sure, let's close this one

[glours]

Hey @paroque28
I was starting working on compose-go and reading the code I figured out that the existing code isn't using the safer way to add a custom label
So if you want to make your first contribution to Docker Compose, we can re-open your PR and I'll let you know how to fix properly the issue directly inside Compose code base!
WDYT?

[paroque28]

Yes! That sounds perfect :)
How can I help you solve this issue?

[paroque28]

@glours done, sorry for the delay.

[glours]

@paroque28 you need to "sign off" your latest commit to make the CI pass

[glours]

LGTM

[hmb]

If the commit message is correct, this might not work. If CustomLabels is nil the code has no effect.

[hmb]

If the commit message is correct, this might not work. If CustomLabels is nil the code has no effect.

My bad, should have looked into the current code, it's already fixed