Add more helpful message for bundle upgrade

Author: amomchilov

bundler/lib/bundler/cli.rb

@@ -185,6 +185,12 @@ def help(cli = nil)
     end
 
     def self.handle_no_command_error(command, has_namespace = $thor_runner)
+      if command == "upgrade"
+        command = Bundler.ui.add_color("bundle update <gem_name>", :bold, :cyan)
+        Bundler.ui.info("Please use #{command} to update gems in your bundle.")
+        return
+      end
+
       if Bundler.settings[:plugins] && Bundler::Plugin.command?(command)
         return Bundler::Plugin.exec_command(command, ARGV[1..-1])
       end

bundler/spec/other/cli_dispatch_spec.rb

@@ -17,4 +17,9 @@
     bundle "in", raise_on_error: false
     expect(err).to eq("Ambiguous command in matches [info, init, install]")
   end
+
+  it "prints a helpful message for 'upgrade'" do
+    bundle "upgrade", raise_on_error: false
+    expect(out).to eq("bundle update")
+  end
 end