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/repository_sync_test.go

@@ -62,6 +62,62 @@ func TestRepoSyncFastForwardsWithoutSwitchingBranches(t *testing.T) {
 	}
 }
 
+func TestRepoSyncUpdatesAForkOrMirrorOnTheServer(t *testing.T) {
+	for _, test := range []struct {
+		name, repo, feedback string
+		requests             []string
+		json                 string
+	}{
+		{
+			name: "fork", repo: `{"full_name":"bob/project","fork":true,"default_branch":"main","parent":{"full_name":"alice/project"}}`,
+			requests: []string{"GET /api/v1/repos/bob/project", "GET /api/v1/repos/bob/project/branches/main", "POST /api/v1/repos/bob/project/merge-upstream", "GET /api/v1/repos/bob/project/branches/main"},
+			feedback: "✓ Synced bob/project main from alice/project (fast-forward 1111111..2222222)\n",
+			json:     `{"branch":"main","commit":"2222222bbbb","previous":"1111111aaaa","remote":"alice/project"}`,
+		},
+		{
+			name: "mirror", repo: `{"full_name":"bob/project","mirror":true,"original_url":"https://example.test/source.git"}`,
+			requests: []string{"GET /api/v1/repos/bob/project", "POST /api/v1/repos/bob/project/mirror-sync"},
+			feedback: "✓ Started updating the mirror bob/project from its source\n",
+			json:     `{"branch":"","commit":"","previous":"","remote":"https://example.test/source.git"}`,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			var requests []string
+			synced := false
+			server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				requests = append(requests, r.Method+" "+r.URL.Path)
+				switch r.URL.Path {
+				case "/api/v1/repos/bob/project":
+					_, _ = w.Write([]byte(test.repo))
+				case "/api/v1/repos/bob/project/branches/main":
+					commit := "1111111aaaa"
+					if synced {
+						commit = "2222222bbbb"
+					}
+					_, _ = w.Write([]byte(`{"name":"main","commit":{"id":"` + commit + `"}}`))
+				case "/api/v1/repos/bob/project/merge-upstream":
+					requirePayload(t, `{"branch":"main","ff_only":true}`, r.Body)
+					synced = true
+					_, _ = w.Write([]byte(`{"merge_type":"fast-forward"}`))
+				default:
+					w.WriteHeader(http.StatusOK)
+				}
+			}))
+			defer server.Close()
+			deps, out, diagnostics := repoTTYDeps(t, server.URL)
+			deps.Git = &syncGit{}
+			require.NoError(t, Execute(context.Background(), deps, []string{"repo", "sync", "bob/project"}))
+			require.Equal(t, test.requests, requests)
+			require.Equal(t, test.feedback, diagnostics.String())
+			require.Empty(t, out.String())
+			deps, out, _ = serverDeps(t, server.URL)
+			deps.Git, synced, requests = &syncGit{}, false, nil
+			require.NoError(t, Execute(context.Background(), deps, []string{"repo", "sync", "bob/project", "--json"}))
+			require.JSONEq(t, test.json, out.String())
+		})
+	}
+}
+
 func TestRepoSyncOutsideACloneExplainsWhatItNeeds(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)
@@ -71,5 +127,5 @@ func TestRepoSyncOutsideACloneExplainsWhatItNeeds(t *testing.T) {
 	deps.Git = &syncGit{}
 	err := Execute(context.Background(), deps, []string{"repo", "sync", "-R", "alice/project", "-b", "main"})
 	require.Equal(t, clierr.Usage, clierr.ExitCode(err), "%v", err)
-	require.ErrorContains(t, err, "repo sync must run inside a Git clone of alice/project")
+	require.ErrorContains(t, err, "repo sync needs a Git clone of alice/project; run it inside one, or pass a fork to update it on the server")
 }