Let a plan of provisions alone fill nothing, so a module not handed can have one for its route (issue 774)

A plan with no templates archive made the client fetch an empty source and fail the module's report. The next
mesh-provisioner composes such plans (a module not handed gets one for what a provider's helper answers, its route), so
this reaches the nodes first.

Quick fix: none (a failed report per routed module). Thorough fix (chosen): a plan with no archive is read as provisions
alone by the one client every node runs.

modules/mesh-provisioner-client/cmd/mesh-provisioner-client/client_test.go

@@ -855,3 +855,19 @@ func TestAFailureKeepsWhenItBeganWhileItsWordsChange(t *testing.T) {
 		}
 	}
 }
+
+// A plan of provisions alone, a module not handed whose route the helper answers (issue 774), names no templates:
+// nothing is fetched and nothing filled, where a fetch of no source failed the module's report.
+func TestAPlanOfProvisionsAloneFetchesNoTemplates(t *testing.T) {
+	s := &templateStore{dir: t.TempDir(), fetch: func(context.Context, string) ([]byte, error) {
+		t.Fatal("a plan with no templates fetched")
+		return nil, nil
+	}}
+	texts, err := s.load(context.Background(), Templates{})
+	if err != nil || len(texts) != 0 {
+		t.Fatalf("loaded %v: %v", texts, err)
+	}
+	if targets, wrong := fillTargets(Plan{}, texts); wrong != "" || len(targets) != 0 {
+		t.Fatalf("filled %v: %s", targets, wrong)
+	}
+}

modules/mesh-provisioner-client/cmd/mesh-provisioner-client/template.go

@@ -69,7 +69,13 @@ type templateStore struct {
 }
 
 // load is every template's text of the archive the plan names, by its path inside the archive.
+//
+// A plan that names no archive is a plan of provisions alone (issue 774: a module not handed has one for what a
+// provider's helper answers of it, its route): there is nothing to fetch and nothing to fill.
 func (s *templateStore) load(ctx context.Context, t Templates) (map[string]string, error) {
+	if t.Source == "" && t.Digest == "" {
+		return map[string]string{}, nil
+	}
 	if texts, ok := s.texts[t.Digest]; ok {
 		return texts, nil
 	}