core: provider has default priority of 5

lib/vagrant/plugin/v2/plugin.rb

@@ -185,9 +185,11 @@ module Vagrant
         # Registers additional providers to be available.
         #
         # @param [Symbol] name Name of the provider.
-        def self.provider(name=UNSET_VALUE, options=nil, &block)
+        def self.provider(name=UNSET_VALUE, **options, &block)
+          options[:priority] ||= 5
+
           components.providers.register(name.to_sym) do
-            [block.call, options || {}]
+            [block.call, options]
           end
 
           nil

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

@@ -249,7 +249,9 @@ describe Vagrant::Plugin::V2::Plugin do
         provider("foo") { "bar" }
       end
 
-      expect(plugin.components.providers[:foo]).to eq(["bar", {}])
+      result = plugin.components.providers[:foo]
+      expect(result[0]).to eq("bar")
+      expect(result[1][:priority]).to eq(5)
     end
 
     it "should register provider classes with options" do
@@ -257,7 +259,10 @@ describe Vagrant::Plugin::V2::Plugin do
         provider("foo", foo: "yep") { "bar" }
       end
 
-      expect(plugin.components.providers[:foo]).to eq(["bar", { foo: "yep" }])
+      result = plugin.components.providers[:foo]
+      expect(result[0]).to eq("bar")
+      expect(result[1][:priority]).to eq(5)
+      expect(result[1][:foo]).to eq("yep")
     end
 
     it "should lazily register provider classes" do