fix(config): skip pure resource provider services in config --images

[TDnorthgarden]

Problem

compose config --images lists the image references of a project's services.
For a provider service declaring neither image: nor build: (a "pure
resource" provider, e.g. a managed database), it printed the
<project>-<service> name that GetImageNameOrDefault fabricates — a
reference that is never built (no build section) and never pulled (the image
phase of up and pull explicitly skips such services, see
pkg/compose/provider_images.go).

Reproducer:

name: edgecase
services:
  db:
    provider:
      type: sbx
  web:
    image: nginx

$ docker compose config --images
nginx
edgecase-db        # fabricated: never built, never pulled

Consumers feeding this output to a registry (e.g.
compose config --images | xargs docker pull) try to pull an image that
does not exist.

Fix

Mirror the pure-resource provider guard of the image phase of up and pull
in config --images: skip services with provider: set and neither
image: nor build:.

[glours]

Review summary: one change needed (config.go:728), the rest is non-blocking.

[glours]

Blocking

This continue also skips the GetDependentImages loop below, so the pre_start hook images of a pure-resource provider service vanish from config --images. pull and up still pull them (pullHookImages and addPreStartHookPulls have no provider guard), and the provider receives the whole resolved service, hooks included, through get-service-config. config --images and pull agreed before this change; they no longer do.

Repro: db with provider: and pre_start: [{image: busybox:1.36.1}], plus web: nginx.

• before: config --images prints edgecase-db, busybox:1.36.1, nginx
• after: prints nginx only, while pull --dry-run still pulls busybox:1.36.1

Only the fabricated name has to go:

pure := s.Provider != nil && s.Image == "" && s.Build == nil
if !pure {
	_, _ = fmt.Fprintln(dockerCli.Out(), api.GetImageNameOrDefault(s, project.Name))
}
for _, img := range api.GetDependentImages(s, project.Name) {
	_, _ = fmt.Fprintln(dockerCli.Out(), img)
}

The current test passes with either version, so it needs a hook case (see the test comment).

[glours]

Non-blocking, follow-up: this is the third spelling of "pure resource provider" (provider_images.go:69-74, and the inverted form in build.go:111 and api.go:311). A small helper next to GetImageNameOrDefault in pkg/api would keep the definition in one place. Fine to do in a separate PR.

[glours]

Nit: "never built or pulled" is not accurate, get-service-config hands that fabricated name to the provider (plugins.go:447). One line is enough, like the guard it mirrors in provider_images.go:

// pure resource provider: no image reference to list

[glours]

Test:

• Add a case with a pre_start hook image on the pure-resource provider, expecting the hook image to be listed (pins the change in config.go).
• Add provider + image: and provider + build: cases, expecting redis and <project>-<service> respectively. They keep the guard narrow.
• cli.EXPECT().Client() and ConfigFile() are never called; only Out() is needed (the test passes without them, and the MockAPIClient goes away too).
• sort.Strings on a one-element slice does nothing. assert.Equal(t, buf.String(), "nginx\n") is stricter and shorter, and drops the sort import.
• ProjectDir: dir is redundant, the compose file's directory is used already.
• Non-blocking: type: sbx ties a core test to one specific provider. The docs use a neutral name (awesomecloud).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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