core: error earlier if adding a path that doesn't exist

CHANGELOG.md

@@ -18,6 +18,7 @@ BUG FIXES:
   - core: Adding a box by path in Cygwin on Windos works. [GH-3132]
   - core: PowerShell scripts work when they're in a directory with
     spaces. [GH-3100]
+  - core: If you add a box path that doesn't exist, error earlier. [GH-3091]
   - guests/darwin: Fix an exception when configuring networks. [GH-3143]
   - hosts/linux: Unusual sed delimiter to avoid conflicts. [GH-3167]
   - providers/virtualbox: Make more internal interactions with VBoxManage

lib/vagrant/action/builtin/box_add.rb

@@ -314,6 +314,9 @@ module Vagrant
                 box_url = download(url, env, show_url: show_url)
                 break
               rescue Errors::DownloaderError => e
+                # If we don't have multiple URLs, just raise the error
+                raise if urls.length == 1
+
                 env[:ui].error(I18n.t(
                   "vagrant.box_download_error",  message: e.message))
                 box_url = nil

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

@@ -164,6 +164,19 @@ describe Vagrant::Action::Builtin::BoxAdd do
         to raise_error(Vagrant::Errors::BoxChecksumMismatch)
     end
 
+    it "raises an error if the box path doesn't exist" do
+      box_path = iso_env.box2_file(:virtualbox)
+
+      env[:box_name] = "foo"
+      env[:box_url] = box_path.to_s + "nope"
+
+      box_collection.should_receive(:add).never
+      app.should_receive(:call).never
+
+      expect { subject.call(env) }.
+        to raise_error(Vagrant::Errors::DownloaderError)
+    end
+
     it "force adds if exists and specified" do
       box_path = iso_env.box2_file(:virtualbox)