Support loading machine configuration without provider validation

Allow Vagrantfile#machine_config to load properly when the requested
provider may not be currently available. Update the Environment to
utilize this when searching for plugin information to properly allow
box provided Vagrantfiles to define required plugins.

lib/vagrant/environment.rb

@@ -955,7 +955,7 @@ module Vagrant
       provider = guess_provider
       vagrantfile.machine_names.each do |mname|
         ldp = @local_data_path.join("machines/#{mname}/#{provider}") if @local_data_path
-        plugins << vagrantfile.machine_config(mname, guess_provider, boxes, ldp)[:config]
+        plugins << vagrantfile.machine_config(mname, guess_provider, boxes, ldp, false)[:config]
       end
       result = plugins.reverse.inject(Vagrant::Util::HashWithIndifferentAccess.new) do |memo, val|
         Vagrant::Util::DeepMerge.deep_merge(memo, val.vagrant.plugins)

lib/vagrant/vagrantfile.rb

@@ -112,7 +112,7 @@ module Vagrant
     # @param [Pathname] data_path Machine data path
     # @return [Hash<Symbol, Object>] Various configuration parameters for a
     #   machine. See the main documentation body for more info.
-    def machine_config(name, provider, boxes, data_path=nil)
+    def machine_config(name, provider, boxes, data_path=nil, validate_provider=true)
       keys = @keys.dup
 
       sub_machine = @config.vm.defined_vms[name]
@@ -127,7 +127,7 @@ module Vagrant
       box_formats      = nil
       if provider != nil
         provider_plugin  = Vagrant.plugin("2").manager.providers[provider]
-        if !provider_plugin
+        if !provider_plugin && validate_provider
           providers  = Vagrant.plugin("2").manager.providers.to_hash.keys
           if providers
             providers_str = providers.join(', ')
@@ -145,18 +145,22 @@ module Vagrant
             machine: name, provider: provider, providers: providers_str
         end
 
-        provider_cls     = provider_plugin[0]
-        provider_options = provider_plugin[1]
-        box_formats      = provider_options[:box_format] || provider
+        if validate_provider
+          provider_cls     = provider_plugin[0]
+          provider_options = provider_plugin[1]
+          box_formats      = provider_options[:box_format] || provider
 
-        # Test if the provider is usable or not
-        begin
-          provider_cls.usable?(true)
-        rescue Errors::VagrantError => e
-          raise Errors::ProviderNotUsable,
-            machine: name.to_s,
-            provider: provider.to_s,
-            message: e.to_s
+          # Test if the provider is usable or not
+          begin
+            provider_cls.usable?(true)
+          rescue Errors::VagrantError => e
+            raise Errors::ProviderNotUsable,
+              machine: name.to_s,
+              provider: provider.to_s,
+              message: e.to_s
+          end
+        else
+          box_formats = provider
         end
       end
 

test/unit/vagrant/vagrantfile_test.rb

@@ -368,6 +368,38 @@ describe Vagrant::Vagrantfile do
         to raise_error(Vagrant::Errors::ProviderNotUsable)
     end
 
+    context "when provider validation is ignored" do
+      before do
+        configure do |config|
+          config.vm.box = "base"
+          config.vm.box_version = "1.0"
+          config.vm.define :guest1
+          config.vm.define :guest2
+
+          config.vm.provider "custom" do |_, c|
+            c.ssh.port = 123
+          end
+        end
+
+        iso_env.box3("base", "1.0", :custom, vagrantfile: <<-VF)
+        Vagrant.configure("2") do |config|
+          config.vagrant.plugins = "vagrant-custom"
+        end
+        VF
+      end
+
+      it "should not raise an error if provider is not found" do
+        expect { subject.machine_config(:guest1, :custom, boxes, nil, false) }.
+          not_to raise_error
+      end
+
+      it "should return configuration from box Vagrantfile" do
+        config = subject.machine_config(:guest1, :custom, boxes, nil, false)[:config]
+        expect(config.vagrant.plugins).to be_a(Hash)
+        expect(config.vagrant.plugins.keys).to include("vagrant-custom")
+      end
+    end
+
     context "local box metadata file" do
       let(:data_path) { double(:data_path) }
       let(:meta_file) { double(:meta_file) }