Fixes #10908: Preserve in-use boxes when force flag is used with prune

Prior to this commit, `vagrant box prune --force` would not prompt a
user to prune Vagrant boxes, even if that box was in use. There was no
way to prune boxes, ignore the prompt, but keep in-use boxes. This
commit adds a new flag that can be combined with `--force`, that will
keep in-use boxes but prune older boxes without prompting the user.

lib/vagrant/action/builtin/box_remove.rb

@@ -99,8 +99,11 @@ module Vagrant
                 b.use Confirm, message, force_key
               end
 
+              # Keep used boxes, even if "force" is applied
+              keep_used_boxes = env[:keep_used_boxes]
+
               result = env[:action_runner].run(stack, env)
-              if !result[:result]
+              if !result[:result] || keep_used_boxes
                 # They said "no", so continue with the next box
                 next
               end

plugins/commands/box/command/prune.rb

@@ -30,6 +30,10 @@ module VagrantPlugins
             o.on("-f", "--force", "Destroy without confirmation even when box is in use.") do |f|
               options[:force] = f
             end
+
+            o.on("-k", "--keep-used-boxes", "When combined with `--force`, will keep boxes still in use.") do |k|
+              options[:keep] = k
+            end
           end
 
           # Parse the options
@@ -41,7 +45,7 @@ module VagrantPlugins
             return @env.ui.warn(I18n.t("vagrant.commands.box.no_installed_boxes"), prefix: false)
           end
 
-          delete_oldest_boxes(boxes, options[:provider], options[:force], options[:name], options[:dry_run])
+          delete_oldest_boxes(boxes, options[:provider], options[:force], options[:name], options[:dry_run], options[:keep])
 
           # Success, exit status 0
           0
@@ -49,7 +53,7 @@ module VagrantPlugins
 
         private
 
-        def delete_oldest_boxes(boxes, only_provider, skip_confirm, only_name, dry_run)
+        def delete_oldest_boxes(boxes, only_provider, skip_confirm, only_name, dry_run, keep_used_boxes)
           # Find the longest box name
           longest_box = boxes.max_by { |x| x[0].length }
           longest_box_length = longest_box[0].length
@@ -112,6 +116,7 @@ module VagrantPlugins
                     box_provider: provider,
                     box_version: version,
                     force_confirm_box_remove: skip_confirm,
+                    keep_used_boxes: keep_used_boxes,
                     box_remove_all_versions: false,
                 })
               end

test/unit/vagrant/action/builtin/box_remove_test.rb

@@ -151,6 +151,37 @@ describe Vagrant::Action::Builtin::BoxRemove do
 
       subject.call(env)
     end
+
+    it "doesn't delete if the box is in use and keep_used_boxes is set" do
+      env[:keep_used_boxes] = true
+      machine_index << new_entry("foo", "virtualbox", "1.0")
+
+      result = { result: true }
+      expect(action_runner).to receive(:run).
+        with(anything, env).and_return(result)
+
+      expect(box_collection).to receive(:find).with(
+        "foo", :virtualbox, "1.0").and_return(box)
+      expect(box).to receive(:destroy!).never
+
+      subject.call(env)
+    end
+
+    it "deletes if the box is in use and force is used" do
+      machine_index << new_entry("foo", "virtualbox", "1.0")
+
+      result = { result: true }
+      expect(action_runner).to receive(:run).
+        with(anything, env).and_return(result)
+
+      expect(box_collection).to receive(:find).with(
+        "foo", :virtualbox, "1.0").and_return(box)
+      expect(box_collection).to receive(:clean).with(box.name)
+        .and_return(true)
+      expect(box).to receive(:destroy!)
+
+      subject.call(env)
+    end
   end
 
   it "errors if the box doesn't exist" do

website/source/docs/cli/box.html.md

@@ -142,6 +142,8 @@ This command removes old versions of installed boxes. If the box is currently in
 
 * `--force` - Destroy without confirmation even when box is in use.
 
+* `--keep-used-boxes` - When combined with `--force`, will keep boxes still in use.
+
 # Box Remove
 
 **Command: `vagrant box remove NAME`**