fix(setup): protect a new GitLab hub's default branch while GitLab still protects it

internal/setup/gitlab.go

@@ -1187,12 +1187,22 @@ func (g *gitlabSetup) defaultBranch(ctx context.Context) {
 			g.r.add(step, StatusWould, "would protect %s: push No one, merge Maintainers, no force push", b)
 			return
 		}
-		if err := g.send(ctx, http.MethodPost, protect, nil, "projects", id(g.hub.ID), "protected_branches"); err != nil {
-			g.r.add(step, StatusFail, "cannot protect %s: %v", b, err)
+		perr := g.send(ctx, http.MethodPost, protect, nil, "projects", id(g.hub.ID), "protected_branches")
+		if perr == nil {
+			g.r.add(step, StatusDone, "protected %s: push No one, merge Maintainers, no force push", b)
+			return
+		}
+		// GitLab protects a new project's default branch from a background
+		// job: the read above may miss a protection the POST then meets
+		// (409). Read it again, and go on as for a branch found protected.
+		if !isStatus(perr, http.StatusConflict) {
+			g.r.add(step, StatusFail, "cannot protect %s: %v", b, perr)
+			return
+		}
+		if err := g.get(ctx, &pb, "projects", id(g.hub.ID), "protected_branches", b); err != nil {
+			g.r.add(step, StatusFail, "cannot protect %s: %v; and reading the protection GitLab reports: %v", b, perr, err)
 			return
 		}
-		g.r.add(step, StatusDone, "protected %s: push No one, merge Maintainers, no force push", b)
-		return
 	}
 	if pushOK(pb.Push) && mergeOK(pb.Merge) && !pb.AllowForcePush {
 		g.r.add(step, StatusOK, "%s is protected: push No one, merge %s, no force push", b, mergeLevels(pb.Merge))

internal/setup/gitlab_test.go

@@ -709,3 +709,16 @@ func TestGitLabWriterOnHub(t *testing.T) {
 		t.Errorf("writer-guard %s %q, exit %d", s.Status, s.Detail, rep.ExitCode())
 	}
 }
+
+// TestGitLabLateProtection: the read of main misses the protection GitLab
+// is still making for the new project, and the POST meets it (409):
+// setup reads it again and protects main as for a branch found protected.
+func TestGitLabLateProtection(t *testing.T) {
+	w := newGLWorld(t, "18.11")
+	w.f.lateProtection = true
+	rep := w.run(t, w.input(false))
+	if s := step(t, rep, "default-branch"); s.Status != StatusDone {
+		t.Errorf("default-branch %s %q", s.Status, s.Detail)
+	}
+	w.checkHub(t, rep)
+}

internal/setup/glfake_test.go

@@ -41,18 +41,22 @@ type glFake struct {
 	t   *testing.T
 	srv *httptest.Server
 
-	mu         sync.Mutex
-	version    string
-	saAPI      bool
-	saCreate   bool
-	premium    bool
-	next       int64
-	users      map[int64]*fUser
-	tokens     map[string]*fToken
-	groups     map[int64]*fGroup
-	projects   map[int64]*fProject
-	writes     []string // "METHOD path" of every request that is not a GET
-	failRoutes map[string]int
+	mu       sync.Mutex
+	version  string
+	saAPI    bool
+	saCreate bool
+	premium  bool
+	// lateProtection makes the first read of a protected branch answer 404
+	// although it exists: GitLab protects a new project's default branch
+	// from a background job, which a read may not see yet.
+	lateProtection bool
+	next           int64
+	users          map[int64]*fUser
+	tokens         map[string]*fToken
+	groups         map[int64]*fGroup
+	projects       map[int64]*fProject
+	writes         []string // "METHOD path" of every request that is not a GET
+	failRoutes     map[string]int
 }
 
 type fUser struct {
@@ -766,6 +770,10 @@ func (f *glFake) serveProject(w http.ResponseWriter, r *http.Request, route stri
 		notFound(w)
 	case "GET projects/:projects/protected_branches/:protected_branches":
 		b := p.branches[s[3]]
+		if f.lateProtection {
+			f.lateProtection = false
+			b = nil
+		}
 		if b == nil {
 			notFound(w)
 			return