change to default state after backend migration

When migrating from a multi-state backend to a single-state backend, we
have to ensure that our locally configured environment is changed back
to "default", or we won't be able to access the new backend.

command/meta_backend_migrate.go

@@ -183,6 +183,10 @@ func (m *Meta) backendMigrateState_S_s(opts *backendMigrateOpts) error {
 
 	// Copy the default state
 	opts.oneEnv = currentEnv
+
+	// now switch back to the default env so we can acccess the new backend
+	m.SetEnv(backend.DefaultStateName)
+
 	return m.backendMigrateState_s_s(opts)
 }
 

command/meta_backend_test.go

@@ -1144,6 +1144,11 @@ func TestMetaBackend_configuredChangeCopy_multiToSingle(t *testing.T) {
 	if _, err := os.Stat(envPath); err != nil {
 		t.Fatal("env should exist")
 	}
+
+	// Verify we are now in the default env, or we may not be able to access the new backend
+	if env := m.Env(); env != backend.DefaultStateName {
+		t.Fatal("using non-default env with single-env backend")
+	}
 }
 
 // Changing a configured backend that supports multi-state to a

command/test-fixtures/backend-change-multi-to-single/.terraform/environment

@@ -0,0 +1 @@
+env1