Add some error handling; tweak.

README.md

@@ -31,9 +31,13 @@ To show all known classes, semesters, and assignments:
 
     rake list
 
-To load a roster for a course semester:
+To load a roster for a specific semester:
 
-    rake roster cs123 sp2016 myroster.csv
+    rake roster cs123 myroster.csv semester=sp16
+
+To load a roster for the current semester:
+
+    rake roster cs123 myroster.csv
 
 ### Grading
 
@@ -83,4 +87,5 @@ repo has changed since the last run. To forcibly regrade:
 
     rake grade cs123 mp1 regrade=yes
 
-You can combine these arguments in any meaningful way.
+You can combine these arguments in any meaningful way. `semester` is available
+for `roster` and `commit`, and and `students` is available for `commit`.

lib/kgrader.rb

@@ -1,5 +1,6 @@
 require_relative 'kgrader/cli'
 require_relative 'kgrader/course'
+require_relative 'kgrader/errors'
 require_relative 'kgrader/filesystem'
 require_relative 'kgrader/roster'
 require_relative 'kgrader/task'

lib/kgrader/cli.rb

@@ -26,17 +26,19 @@ module KGrader
     end
 
     def roster(course, semester, rosterfile)
-      Course.new(@fs, course).roster(semester).load rosterfile
+      course = fetch_course course
+      semester ||= course.current_semester
+      course.roster(semester).load rosterfile
     end
 
     def grade(course, semester, assignment, options = {})
-      course = Course.new @fs, course
+      course = fetch_course course
       semester ||= course.current_semester
       course.task(semester, assignment).grade options
     end
 
     def commit(course, semester, assignment, options = {})
-      course = Course.new @fs, course
+      course = fetch_course course
       semester ||= course.current_semester
       course.task(semester, assignment).commit options
     end
@@ -56,6 +58,12 @@ module KGrader
     end
 
     private
+    def fetch_course(course)
+      Course.new(@fs, course)
+    rescue FilesystemError
+      KGrader::die "unknown course"
+    end
+
     def reset_jail
       FileUtils.rm_rf @fs.jail
       FileUtils.mkdir @fs.jail

lib/kgrader/errors.rb

@@ -0,0 +1,7 @@
+module KGrader
+  class KGraderError < StandardError
+  end
+
+  class FilesystemError < KGraderError
+  end
+end

lib/kgrader/filesystem.rb

@@ -51,7 +51,11 @@ module KGrader
         YAML.load File.read(path)
       when '.csv'
         File.read(path).split("\n").map! { |line| line.split "," }
+      else
+        raise FilesystemError, "unknown file type"
       end
+    rescue SystemCallError  # Errno::ENOENT, etc.
+      raise FilesystemError, "can't read file"
     end
   end
 end

lib/kgrader/util.rb

@@ -1,7 +1,7 @@
 require 'date'
 
 module KGrader
-  def self.abort(error)
+  def self.die(error)
     Kernel::abort "fatal: #{error}"
   end
 
@@ -13,7 +13,7 @@ module KGrader
       if arg.include? '='
         key, val = arg.split('=', 2)
         key = key.to_sym
-        abort "unknown keyword #{key}" unless keywords.include? key
+        die "unknown keyword #{key}" unless keywords.include? key
         options[key] = case keywords[key]
         when :string
           val
@@ -29,8 +29,8 @@ module KGrader
       end
     end
 
-    abort "too few arguments" if args.size < num
-    abort "too many arguments" if args.size > num
+    die "too few arguments" if args.size < num
+    die "too many arguments" if args.size > num
     return args, options
   end
 

rakefile

@@ -15,7 +15,7 @@ task :default => :help do ; end
 task :help do
   puts %{usage:
 - rake list
-- rake roster <course> <semester> <rosterfile>
+- rake roster <course> <rosterfile> [semester=<...>]
 - rake grade  <course> <assignment> [semester=<...>] [students=<...>]
               [due=<...>] [fetch=<yes/no>] [regrade=<yes/no>]
 - rake commit <course> <assignment> [semester=<...>] [students=<...>]
@@ -28,8 +28,8 @@ task :list do
 end
 
 task :roster do
-  course, semester, rosterfile = parse_args 3
-  cli.roster course, semester, rosterfile
+  course, rosterfile, options = parse_args 2, { :semester => :string }
+  cli.roster course, options[:semester], rosterfile
 end
 
 task :grade do