Raise an error if disk files are re-used in config

plugins/kernel_v2/config/vm.rb

@@ -914,6 +914,13 @@ module VagrantPlugins
                            name: duplicate_names)
         end
 
+        disk_files = @disks.select { |d| d.type == :disk }.map { |d| d.file }
+        duplicate_files = disk_files.detect { |d| disk_files.count(d) > 1 }
+        if duplicate_files && duplicate_files.size
+          errors << I18n.t("vagrant.config.vm.multiple_disk_files_error",
+                           file: duplicate_files)
+        end
+
         @disks.each do |d|
           error = d.validate(machine)
           errors.concat error if !error.empty?

templates/locales/en.yml

@@ -1972,6 +1972,12 @@ en:
           Ignoring provider config for validation...
         multiple_primary_disks_error: |-
           There are more than one primary disks defined for guest '%{name}'. Please ensure that only one disk has been defined as a primary disk.
+        multiple_disk_files_error: |-
+          The following disk file is used multiple times in the disk configuration:
+
+          %{file}
+
+          Each disk file may only be attached to a VM once.
         multiple_disk_names_error: |-
           Duplicate disk names defined: '%{name}'. Disk names must be unique.
         multiple_networks_set_hostname: "Multiple networks have set `:hostname`"

test/unit/plugins/kernel_v2/config/vm_test.rb

@@ -622,6 +622,22 @@ describe VagrantPlugins::Kernel_V2::VMConfig do
       assert_invalid
     end
 
+    it "raises an error with duplicate disk files" do
+      allow(File).to receive(:file?).with("bar.vmdk").and_return(true)
+      subject.disk(:disk, size: 100, name: "foo1", file: "bar.vmdk")
+      subject.disk(:disk, size: 100, name: "foo2", file: "bar.vmdk")
+      subject.finalize!
+      assert_invalid
+    end
+
+    it "does not raise an error with duplicate dvd files" do
+      allow(File).to receive(:file?).with("bar.iso").and_return(true)
+      subject.disk(:dvd, name: "foo1", file: "bar.iso")
+      subject.disk(:dvd, name: "foo2", file: "bar.iso")
+      subject.finalize!
+      assert_valid
+    end
+
     it "does not merge duplicate disks" do
       subject.disk(:disk, size: 1000, primary: false, name: "storage")
       subject.disk(:disk, size: 1000, primary: false, name: "backup")