Add helpful invalid gemspec error message for bundle install --standalone

lib/bundler/installer/standalone.rb

@@ -44,6 +44,9 @@ def bundler_path
     def gem_path(path, spec)
       full_path = Pathname.new(path).absolute? ? path : File.join(spec.full_gem_path, path)
       Pathname.new(full_path).relative_path_from(Bundler.root.join(bundler_path)).to_s
+    rescue TypeError
+      error_message = "#{spec.name} #{spec.version} has an invalid gemspec"
+      raise Gem::InvalidSpecificationException.new(error_message)
     end
   end
 end

spec/install/gems/standalone_spec.rb

@@ -303,4 +303,18 @@
       expect(extension_line).to eq "$:.unshift File.expand_path '../../bundle', __FILE__"
     end
   end
+
+  describe "with gem that has an invalid gemspec" do
+    before do
+      install_gemfile <<-G, :standalone => true
+        source 'https://rubygems.org'
+        gem "resque-scheduler", "2.2.0"
+      G
+    end
+
+    it "outputs a helpful error message" do
+      expect(out).to include("You have one or more invalid gemspecs that need to be fixed.")
+      expect(out).to include("resque-scheduler 2.2.0 has an invalid gemspec")
+    end
+  end
 end