AngularJS constants

You are correct, it’s impossible to register both foo and bar as constants.

Also for using a provider as a workaround, you almost got it right except that you have to store data in a provider instance:

var app = angular.module('myApp', []);

app.constant('foo', {
    message: 'Hello'
});

app.provider('bar', ['foo', function(foo) {
  this.data = {
    message: foo.message + ' World!'
  };

  this.$get = function() {
    return this.data;
  };
}]);

and then in config block, inject a bar’s provider instance (not a bar instance as it isn’t available yet in the config phase):

app.config(['barProvider', function(barProvider) {
  console.log(barProvider.data.message);
}]);

Hope this helps.