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/app/repo_mutations_test.go

@@ -159,6 +159,67 @@ func TestRenamedURL(t *testing.T) {
 	}
 }
 
+func TestRepoForkReportsAnExistingFork(t *testing.T) {
+	var requests []string
+	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		requests = append(requests, r.Method+" "+r.URL.Path)
+		switch r.Method + " " + r.URL.Path {
+		case "POST /api/v1/repos/bob/project/forks":
+			w.WriteHeader(http.StatusConflict)
+			_, _ = w.Write([]byte(`{"message":"repository is already forked by user [uname: alice, repo path: bob/project, fork path: alice/project-fork]"}`))
+		case "GET /api/v1/repos/bob/project/forks":
+			if r.URL.Query().Get("page") != "1" {
+				_, _ = w.Write([]byte(`[]`))
+				return
+			}
+			_, _ = w.Write([]byte(`[{"full_name":"carol/project","owner":{"login":"carol"}},{"full_name":"alice/project-fork","owner":{"login":"alice"}}]`))
+		case "GET /api/v1/repos/alice/project-fork":
+			_, _ = w.Write([]byte(`{"full_name":"alice/project-fork","fork":true,"html_url":"https://gitea.test/alice/project-fork","parent":{"full_name":"bob/project"}}`))
+		default:
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer server.Close()
+	deps, out, diagnostics := repoTTYDeps(t, server.URL)
+	require.NoError(t, Execute(context.Background(), deps, []string{"repo", "fork", "bob/project"}))
+	require.Equal(t, "! alice/project-fork already exists\n", diagnostics.String())
+	require.Equal(t, "https://gitea.test/alice/project-fork\n", out.String())
+	require.Equal(t, "GET /api/v1/repos/alice/project-fork", requests[len(requests)-1])
+}
+
+func TestRepoForkRefusesTheOwnersRepository(t *testing.T) {
+	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Errorf("unexpected request %s %s", r.Method, r.URL.Path)
+	}))
+	defer server.Close()
+	deps, _, _ := serverDeps(t, server.URL)
+	err := Execute(context.Background(), deps, []string{"repo", "fork", "alice/project"})
+	require.Equal(t, clierr.Usage, clierr.ExitCode(err), "%v", err)
+	require.ErrorContains(t, err, "cannot fork alice/project into alice: it already owns it; pass --org")
+}
+
+func TestRepoForkAddsTheForkAsOrigin(t *testing.T) {
+	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		require.Equal(t, "POST /api/v1/repos/bob/project/forks", r.Method+" "+r.URL.Path)
+		requirePayload(t, `{"name":"mine"}`, r.Body)
+		_, _ = fmt.Fprintf(w, `{"full_name":"alice/mine","html_url":"https://gitea.test/alice/mine","clone_url":"http://%s/alice/mine.git"}`, r.Host)
+	}))
+	defer server.Close()
+	deps, out, diagnostics := repoTTYDeps(t, server.URL)
+	fork := server.URL + "/alice/mine.git"
+	runner := &fakeGit{results: map[string]string{
+		"rev-parse --is-inside-work-tree": "true",
+		"remote get-url origin":           server.URL + "/bob/project.git",
+		"remote rename origin upstream":   "",
+		"remote add -- origin " + fork:    "",
+	}}
+	deps.Git = runner
+	require.NoError(t, Execute(context.Background(), deps, []string{"repo", "fork", "bob/project", "--fork-name", "mine", "--remote"}))
+	require.Equal(t, []string{"rev-parse --is-inside-work-tree", "remote get-url origin", "remote rename origin upstream", "remote add -- origin " + fork}, runner.calls)
+	require.Equal(t, "✓ Forked bob/project to alice/mine\n✓ Renamed Git remote origin to upstream\n✓ Added Git remote origin for alice/mine\n", diagnostics.String())
+	require.Equal(t, "https://gitea.test/alice/mine\n", out.String())
+}
+
 func TestRepoDeleteReportsTheDeletion(t *testing.T) {
 	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		require.Equal(t, http.MethodDelete+" /api/v1/repos/alice/x", r.Method+" "+r.URL.Path)