Environment can_install_provider and install_provider

lib/vagrant/environment.rb

@@ -383,6 +383,26 @@ module Vagrant
       raise Errors::NoDefaultProvider
     end
 
+    # Returns whether or not we know how to install the provider with
+    # the given name.
+    #
+    # @return [Boolean]
+    def can_install_provider?(name)
+      host.capability?(provider_install_key(name))
+    end
+
+    # Installs the provider with the given name.
+    #
+    # This will raise an exception if we don't know how to install the
+    # provider with the given name. You should guard this call with
+    # `can_install_provider?` for added safety.
+    #
+    # An exception will be raised if there are any failures installing
+    # the provider.
+    def install_provider(name)
+      host.capability(provider_install_key(name))
+    end
+
     # Returns the collection of boxes for the environment.
     #
     # @return [BoxCollection]
@@ -883,6 +903,12 @@ module Vagrant
       nil
     end
 
+    # Returns the key used for the host capability for provider installs
+    # of the given name.
+    def provider_install_key(name)
+      "provider_install_#{name}".to_sym
+    end
+
     # This upgrades a home directory that was in the v1.1 format to the
     # v1.5 format. It will raise exceptions if anything fails.
     def upgrade_home_path_v1_1

lib/vagrant/plugin/v2/provider.rb

@@ -24,6 +24,21 @@ module Vagrant
           true
         end
 
+        # This is called early, before a machine is instantiated, to check
+        # if this provider is installed. This should return true or false.
+        #
+        # If the provider is not installed and Vagrant determines it is
+        # able to install this provider, then it will do so. Installation
+        # is done by calling Environment.install_provider.
+        #
+        # If Environment.can_install_provider? returns false, then an error
+        # will be shown to the user.
+        def self.installed?
+          # By default return true for backwards compat so all providers
+          # continue to work.
+          true
+        end
+
         # Initialize the provider to represent the given machine.
         #
         # @param [Vagrant::Machine] machine The machine that this provider

test/unit/vagrant/environment_test.rb

@@ -25,6 +25,48 @@ describe Vagrant::Environment do
   let(:instance)  { env.create_vagrant_env }
   subject { instance }
 
+  describe "#can_install_provider?" do
+    let(:plugin_hosts) { {} }
+    let(:plugin_host_caps) { {} }
+
+    before do
+      m = Vagrant.plugin("2").manager
+      m.stub(hosts: plugin_hosts)
+      m.stub(host_capabilities: plugin_host_caps)
+
+      # Detect the host
+      env.vagrantfile <<-VF
+      Vagrant.configure("2") do |config|
+        config.vagrant.host = nil
+      end
+      VF
+
+      # Setup the foo host by default
+      plugin_hosts[:foo] = [detect_class(true), nil]
+    end
+
+    it "should return whether it can install or not" do
+      plugin_host_caps[:foo] = { provider_install_foo: Class }
+
+      expect(subject.can_install_provider?(:foo)).to be_true
+      expect(subject.can_install_provider?(:bar)).to be_false
+    end
+  end
+
+  describe "#install_provider" do
+    let(:host) { double(:host) }
+
+    before do
+      allow(subject).to receive(:host).and_return(host)
+    end
+
+    it "should install the correct provider" do
+      expect(host).to receive(:capability).with(:provider_install_foo)
+
+      subject.install_provider(:foo)
+    end
+  end
+
   describe "#home_path" do
     it "is set to the home path given" do
       Dir.mktmpdir do |dir|

test/unit/vagrant/plugin/v2/provider_test.rb

@@ -12,6 +12,10 @@ describe Vagrant::Plugin::V2::Provider do
     expect(described_class).to be_usable
   end
 
+  it "should be installed by default" do
+    expect(described_class).to be_installed
+  end
+
   it "should return nil by default for actions" do
     expect(instance.action(:whatever)).to be_nil
   end