registry: deprecate RepositoryInfo.Official field

[thaJeztah]

• relates to Cleanup: Replace ResolveRepositoryName with RepositoryInfo{} #8456
• relates to Improve documentation and golint compliance of registry package #14835

This field indicates whether a repository is an official image (Docker Library / Docker Official Images). This information is deducted from the image reference, and not used anywhere, other than in tests.

The RepositoryInfo and IndexInfo types were originally introduced in 568f86e, with their fields documented in 4fcb9ac.

At the time, the Official field was only used for docker push to produce a custom error message if someone would attempt to push an official image to docker hub (assuming nobody would be able to do so);

moby/api/client/commands.go

Lines 1184 to 1194 in 6870bde

	// If we're not using a custom registry, we know the restrictions
	// applied to repository names and can warn the user in advance.
	// Custom repositories can have different rules, and we must also
	// allow pushing by image ID.
	if repoInfo.Official {
	username := authConfig.Username
	if username == "" {
	username = "<user>"
	}
	return fmt.Errorf("You cannot push a \"root\" repository. Please rename your repository to <user>/<repo> (ex: %s/%s)", username, repoInfo.LocalName)
	}

Before that commit, the condition for this error message was based on the given image reference directly; b370acd

moby/commands.go

Lines 421 to 428 in b370acd

	tmp := strings.SplitN(local, "/", 2)
	if len(tmp) == 1 {
	return fmt.Errorf(
	"Impossible to push a \"root\" repository. Please rename your repository in <user>/<repo> (ex: %s/%s)",
	srv.runtime.authConfig.Username, local)
	} else {
	remote = local
	}

This patch deprecates the field, because it's not used, and removes tests related to it.

- Human readable description for the release notes

Go SDK: `registry`: Deprecate `RepositoryInfo.Official` field

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