feat(repo): sync forks on the server, wire forks into clones, validate set-default

repo sync OWNER/REPO, run where no Git remote points to the repository,
now updates it on the server: a fork's branch fast-forwards to its
parent's through merge-upstream, and a pull mirror fetches its source.

repo fork reports an existing fork ("! bob/x already exists") instead of
a raw HTTP 409, refuses to fork a repository into its own owner, and
gains --fork-name, --clone (Git flags after --) and --remote, which adds
the fork as origin and renames the old origin to upstream.

repo clone passes Git flags after --, and takes --upstream-remote-name
and --no-upstream for forks. Clones report what they set up.

repo set-default checks that the repository exists before saving it,
prints the saved repository with --view, removes it with --unset, and
reports the change.

Signed-off-by: bircni <bircni@icloud.com>

internal/services/repositories.go

@@ -184,13 +184,67 @@ func (s Repositories) Delete(ctx context.Context, repo string) error {
 	})
 }
 
-// Fork creates a fork for the current user or selected organization.
-func (s Repositories) Fork(ctx context.Context, repo, org string) (Repository, error) {
+// ForkOptions places a fork: under Organization instead of the account, and named Name instead
+// of the forked repository's name.
+type ForkOptions struct{ Organization, Name string }
+
+// Fork forks repo for the account or the organization. When that owner already has a fork of
+// repo, Fork returns it and reports that it existed.
+func (s Repositories) Fork(ctx context.Context, repo string, opts ForkOptions) (Repository, bool, error) {
 	var options gitea.CreateForkOption
-	if org != "" {
-		options.Organization = &org
+	if opts.Organization != "" {
+		options.Organization = &opts.Organization
 	}
-	return repoConvert(ctx, s.Client, repo, repositoryFrom, func(ctx context.Context, c *gitea.Client, owner, name string) (*gitea.Repository, *gitea.Response, error) {
+	if opts.Name != "" {
+		options.Name = &opts.Name
+	}
+	fork, err := repoConvert(ctx, s.Client, repo, repositoryFrom, func(ctx context.Context, c *gitea.Client, owner, name string) (*gitea.Repository, *gitea.Response, error) {
 		return c.Repositories.CreateFork(ctx, owner, name, options)
 	})
+	apiErr, ok := errors.AsType[*transport.APIError](err)
+	if !ok || apiErr.Status != http.StatusConflict || !strings.Contains(apiErr.Message, "already forked") {
+		return fork, false, err
+	}
+	owner := opts.Organization
+	if owner == "" {
+		if owner, err = CurrentAccount(ctx, s.Client); err != nil {
+			return Repository{}, false, err
+		}
+	}
+	forks, listErr := listAll(func(page int) ([]*gitea.Repository, error) {
+		return repoCall(ctx, s.Client, repo, func(ctx context.Context, c *gitea.Client, owner, name string) ([]*gitea.Repository, *gitea.Response, error) {
+			return c.Repositories.ListForks(ctx, owner, name, gitea.ListForksOptions{ListOptions: listOptions(50, page)})
+		})
+	})
+	if listErr != nil {
+		return Repository{}, false, listErr
+	}
+	for _, existing := range forks {
+		if existing.Owner != nil && strings.EqualFold(existing.Owner.UserName, owner) {
+			// The fork list omits the parent that a fork's own record has.
+			fork, err := s.View(ctx, existing.FullName)
+			return fork, err == nil, err
+		}
+	}
+	return Repository{}, false, apiErr
+}
+
+// MergeUpstream fast-forwards branch of the fork repo to its parent's branch on the server. It
+// returns how Gitea updated the branch: "fast-forward", or "up-to-date" when there was nothing to do.
+func (s Repositories) MergeUpstream(ctx context.Context, repo, branch string) (string, error) {
+	result, err := repoCall(ctx, s.Client, repo, func(ctx context.Context, c *gitea.Client, owner, name string) (*gitea.MergeUpstreamResponse, *gitea.Response, error) {
+		return c.Repositories.MergeUpstream(ctx, owner, name, gitea.MergeUpstreamRequest{Branch: branch, FfOnly: true})
+	})
+	if err != nil {
+		return "", err
+	}
+	return result.MergeStyle, nil
+}
+
+// MirrorSync asks the server to update the pull mirror repo from its source; the update runs in
+// the background.
+func (s Repositories) MirrorSync(ctx context.Context, repo string) error {
+	return repoDo(ctx, s.Client, repo, func(ctx context.Context, c *gitea.Client, owner, name string) (*gitea.Response, error) {
+		return c.Repositories.MirrorSync(ctx, owner, name)
+	})
 }