Fix init and other commands that run without a project

The Basis needs to be able to respond to Vagrantfile() and
DefaultProvider() to make it through Vagrant::Environment
initialization.

Depends on https://github.com/hashicorp/vagrant-plugin-sdk/pull/178

internal/core/basis.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"sync"
 
@@ -12,6 +13,7 @@ import (
 	"github.com/hashicorp/go-hclog"
 	"github.com/hashicorp/go-multierror"
 	goplugin "github.com/hashicorp/go-plugin"
+	"github.com/pkg/errors"
 	"google.golang.org/protobuf/proto"
 
 	"github.com/hashicorp/vagrant-plugin-sdk/component"
@@ -404,6 +406,96 @@ func (b *Basis) DefaultPrivateKey() (path path.Path, err error) {
 	return b.dir.DataDir().Join("insecure_private_key"), nil
 }
 
+// DefaultProvider implements core.Basis
+// This is a subset of the Project.DefaultProvider() algorithm, just the parts
+// that make sense when you don't have a Vagrantfile
+func (b *Basis) DefaultProvider() (string, error) {
+	logger := b.logger.Named("default-provider")
+	logger.Debug("Searching for default provider")
+
+	defaultProvider := os.Getenv("VAGRANT_DEFAULT_PROVIDER")
+	if defaultProvider != "" {
+		logger.Debug("Using VAGRANT_DEFAULT_PROVIDER", "provider", defaultProvider)
+		return defaultProvider, nil
+	}
+
+	usableProviders := []*core.NamedPlugin{}
+	pluginProviders, err := b.plugins.ListPlugins("provider")
+	if err != nil {
+		return "", err
+	}
+	for _, pp := range pluginProviders {
+		logger.Debug("considering plugin", "provider", pp.Name)
+
+		plug, err := b.plugins.GetPlugin(pp.Name, pp.Type)
+		if err != nil {
+			return "", err
+		}
+
+		plugOpts := plug.Options.(*component.ProviderOptions)
+		logger.Debug("got provider options", "options", fmt.Sprintf("%#v", plugOpts))
+
+		// Skip providers that can't be defaulted.
+		if !plugOpts.Defaultable {
+			logger.Debug("skipping non-defaultable provider", "provider", pp.Name)
+			continue
+		}
+
+		// Skip the providers that aren't usable.
+		logger.Debug("Checking usable on provider", "provider", pp.Name)
+		pluginImpl := plug.Plugin.(core.Provider)
+		usable, err := pluginImpl.Usable()
+		if err != nil {
+			return "", err
+		}
+		if !usable {
+			logger.Debug("Skipping unusable provider", "provider", pp.Name)
+			continue
+		}
+
+		// If we made it here we have a candidate usable provider
+		usableProviders = append(usableProviders, plug)
+	}
+	logger.Debug("Initial usable provider list", "usableProviders", usableProviders)
+
+	// Sort by plugin priority, higher is first
+	sort.SliceStable(usableProviders, func(i, j int) bool {
+		iPriority := usableProviders[i].Options.(*component.ProviderOptions).Priority
+		jPriority := usableProviders[j].Options.(*component.ProviderOptions).Priority
+		return iPriority > jPriority
+	})
+	logger.Debug("Priority sorted usable provider list", "usableProviders", usableProviders)
+
+	preferredProviders := strings.Split(os.Getenv("VAGRANT_PREFERRED_PROVIDERS"), ",")
+	k := 0
+	for _, pp := range preferredProviders {
+		spp := strings.TrimSpace(pp) // .map { s.strip }
+		if spp != "" {               // .select { !s.empty? }
+			preferredProviders[k] = spp
+			k++
+		}
+	}
+	preferredProviders = preferredProviders[:k]
+
+	for _, pp := range preferredProviders {
+		for _, up := range usableProviders {
+			if pp == up.Name {
+				logger.Debug("Using preffered provider found in usable list",
+					"provider", pp)
+				return pp, nil
+			}
+		}
+	}
+
+	if len(usableProviders) > 0 {
+		logger.Debug("Using the first provider from the usable list",
+			"provider", usableProviders[0])
+		return usableProviders[0].Name, nil
+	}
+
+	return "", errors.New("No default provider.")
+}
+
 // Implements core.Basis
 // Returns all the registered plugins of the types specified
 func (b *Basis) Plugins(types ...string) (plugins []*core.NamedPlugin, err error) {
@@ -801,6 +893,10 @@ func (b *Basis) TargetIndex() (core.TargetIndex, error) {
 	return b.index, nil
 }
 
+func (b *Basis) Vagrantfile() (core.Vagrantfile, error) {
+	return b.vagrantfile, nil
+}
+
 // Returns the list of all known components
 func (b *Basis) Components(ctx context.Context) ([]*Component, error) {
 	return b.components(b.ctx)

lib/vagrant/environment/remote.rb

@@ -102,7 +102,7 @@ module Vagrant
       end
 
       def default_provider(**opts)
-        client.respond_to?(:default_provider) && client.default_provider(opts)
+        client.default_provider(**opts)
       end
 
       # Gets a target (machine) by name

lib/vagrant/protobufs/proto/vagrant_plugin_sdk/plugin_pb.rb

@@ -660,6 +660,9 @@ Google::Protobuf::DescriptorPool.generated_pool.build do
     add_message "hashicorp.vagrant.sdk.Basis.ResourceIdResponse" do
       optional :resource_id, :string, 1
     end
+    add_message "hashicorp.vagrant.sdk.Basis.DefaultProviderResponse" do
+      optional :provider_name, :string, 1
+    end
     add_message "hashicorp.vagrant.sdk.Target" do
     end
     add_message "hashicorp.vagrant.sdk.Target.ResourceIdResponse" do
@@ -1164,6 +1167,7 @@ module Hashicorp
       Ref::Machine = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Ref.Machine").msgclass
       Basis = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Basis").msgclass
       Basis::ResourceIdResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Basis.ResourceIdResponse").msgclass
+      Basis::DefaultProviderResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Basis.DefaultProviderResponse").msgclass
       Target = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Target").msgclass
       Target::ResourceIdResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Target.ResourceIdResponse").msgclass
       Target::RecordResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("hashicorp.vagrant.sdk.Target.RecordResponse").msgclass

lib/vagrant/protobufs/proto/vagrant_plugin_sdk/plugin_services_pb.rb

@@ -356,14 +356,16 @@ module Hashicorp
           self.unmarshal_class_method = :decode
           self.service_name = 'hashicorp.vagrant.sdk.BasisService'
 
+          rpc :Boxes, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::BoxCollection
           rpc :CWD, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::Path
           rpc :DataDir, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::DataDir::Basis
           rpc :DefaultPrivateKey, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::Path
-          rpc :UI, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::TerminalUI
+          rpc :DefaultProvider, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Basis::DefaultProviderResponse
           rpc :Host, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::Host
-          rpc :Boxes, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::BoxCollection
-          rpc :TargetIndex, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::TargetIndex
           rpc :ResourceId, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Basis::ResourceIdResponse
+          rpc :TargetIndex, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::TargetIndex
+          rpc :Vagrantfile, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::Vagrantfile
+          rpc :UI, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::TerminalUI
           rpc :Seed, ::Hashicorp::Vagrant::Sdk::Args::Seeds, ::Google::Protobuf::Empty
           rpc :Seeds, ::Google::Protobuf::Empty, ::Hashicorp::Vagrant::Sdk::Args::Seeds
         end

plugins/commands/serve/client/basis.rb

@@ -30,6 +30,11 @@ module VagrantPlugins
           resp.path
         end
 
+        def default_provider(**opts)
+          resp = client.default_provider(Empty.new)
+          resp.provider_name.to_sym
+        end
+
         def target_index
           TargetIndex.load(
             client.target_index(Empty.new),
@@ -37,6 +42,10 @@ module VagrantPlugins
           )
         end
 
+        def vagrantfile
+          client.vagrantfile(Empty.new).to_ruby
+        end
+
         # @return [Terminal]
         def ui
           begin