Invalid assessment config SyntaxError not caught on create

[michellexliu]

Steps To Reproduce
Steps to reproduce the behavior:

1. Create a lab with a .rb config file that has a syntax error
2. Create a tarfile of the lab
3. Click install assessment
4. Click "browse" under "Import from tarball"
5. Select the tarfile for the lab

Current behavior
An error page is shown on the deployed version, locally this is shown:

The assignment is also created but shows an error whenever you try to access it.

Expected behavior
Similar behavior to when you edit an existing config and click reload config (see #1522). No assignment should be created.

[damianhxy]

Also not caught on import from file system. But this can only occur if a user that has an assessment with invalid config directly navigates to the edit assessment page and deletes the assessment. And ultimately, other errors such as NameError and ArgumentError would not be caught, so it might be pointless trying to preempt this.

[damianhxy]

If we aren't too concerned with generating an error page, the following patch would probably suffice:

diff --git a/app/controllers/assessments_controller.rb b/app/controllers/assessments_controller.rb
index 8988bba0..96ba0c9f 100755
--- a/app/controllers/assessments_controller.rb
+++ b/app/controllers/assessments_controller.rb
@@ -145,7 +145,7 @@ class AssessmentsController < ApplicationController
         redirect_to(action: "install_assessment")
         return
       end
-    rescue StandardError => e
+    rescue StandardError, SyntaxError => e
       flash[:error] = "Error while reading the tarball -- #{e.message}."
       redirect_to(action: "install_assessment")
       return
@@ -850,7 +850,11 @@ private
       else
         return false unless asmt_name
 
-        asmt_rb_exists = true if pathname == "#{asmt_name}/#{asmt_name}.rb"
+        if pathname == "#{asmt_name}/#{asmt_name}.rb"
+          config_source = entry.read
+          RubyVM::InstructionSequence.compile(config_source)
+          asmt_rb_exists = true
+        end
         asmt_yml_exists = true if pathname == "#{asmt_name}/#{asmt_name}.yml"
       end
     end

Giving us an error that looks like

[damianhxy]

If we really wanted to handle import from file system too, one option is something like

def importAssessment
    @assessment = @course.assessments.new(name: params[:assessment_name])
    begin
      @assessment.load_config_file # only call this on saved assessments
    rescue SyntaxError => e
      flash[:error] = "Error while importing assessment -- #{e.message}"
      redirect_to(action: "install_assessment") && return
    end
    @assessment.load_yaml # this will save the assessment
    @assessment.load_embedded_quiz # this will check and load embedded quiz
    @assessment.construct_folder # make sure there's a handin folder, just in case
    redirect_to([@course, @assessment])
  end