core: Box#in_use? as an API

lib/vagrant/action/builtin/box_remove.rb

@@ -73,21 +73,8 @@ module Vagrant
 
           # Verify that this box is not in use by an active machine,
           # otherwise warn the user.
-          users = []
-          env[:machine_index].each do |entry|
-            box_data = entry.extra_data["box"]
-            next if !box_data
-
-            # If all the data matches AND the entry is a seemingly
-            # valid entry, then track it.
-            if box_data["name"] == box.name &&
-              box_data["provider"] == box.provider.to_s &&
-              box_data["version"] == box.version.to_s &&
-              entry.valid?(env[:home_path])
-              users << entry
-            end
-          end
-
+          users = box.in_use?(env[:machine_index]) || []
+          users = users.find_all { |u| u.valid?(env[:home_path]) }
           if !users.empty?
             # Build up the output to show the user.
             users = users.map do |entry|

lib/vagrant/box.rb

@@ -85,6 +85,33 @@ module Vagrant
       return true
     end
 
+    # Checks if this box is in use according to the given machine
+    # index and returns the entries that appear to be using the box.
+    #
+    # The entries returned, if any, are not tested for validity
+    # with {MachineIndex::Entry#valid?}, so the caller should do that
+    # if the caller cares.
+    #
+    # @param [MachineIndex] index
+    # @return [Array<MachineIndex::Entry>]
+    def in_use?(index)
+      results = []
+      index.each do |entry|
+        box_data = entry.extra_data["box"]
+        next if !box_data
+
+        # If all the data matches, record it
+        if box_data["name"] == self.name &&
+          box_data["provider"] == self.provider.to_s &&
+          box_data["version"] == self.version.to_s
+          results << entry
+        end
+      end
+
+      return nil if results.empty?
+      results
+    end
+
     # Loads the metadata URL and returns the latest metadata associated
     # with this box.
     #

test/unit/vagrant/box_test.rb

@@ -195,6 +195,36 @@ describe Vagrant::Box do
     end
   end
 
+  context "#in_use?" do
+    let(:index) { [] }
+
+    def new_entry(name, provider, version)
+      Vagrant::MachineIndex::Entry.new.tap do |entry|
+        entry.extra_data["box"] = {
+          "name" => name,
+          "provider" => provider,
+          "version" => version,
+        }
+      end
+    end
+
+    it "returns nil if the index has no matching entries" do
+      index << new_entry("foo", "bar", "1.0")
+      index << new_entry("foo", "baz", "1.2")
+
+      expect(subject).to_not be_in_use(index)
+    end
+
+    it "returns matching entries if they exist" do
+      matching = new_entry(name, provider.to_s, version)
+      index << new_entry("foo", "bar", "1.0")
+      index << matching
+      index << new_entry("foo", "baz", "1.2")
+
+      expect(subject.in_use?(index)).to eq([matching])
+    end
+  end
+
   context "#load_metadata" do
     let(:metadata_url) do
       Tempfile.new("vagrant").tap do |f|