Merge pull request #4673 from rolandwalker/cask_load_exceptions

Improve error checking and messages on Cask load

lib/cask/source/path_base.rb

@@ -15,8 +15,23 @@ class Cask::Source::PathBase
   end
 
   def load
-    require path
-    Cask.const_get(cask_class_name).new
+    raise CaskError.new "File '#{path}' does not exist"      unless path.exist?
+    raise CaskError.new "File '#{path}' is not readable"     unless path.readable?
+    raise CaskError.new "File '#{path}' is not a plain file" unless path.file?
+    begin
+      require path
+    rescue CaskError, StandardError, ScriptError => e
+      # bug: e.message.concat doesn't work with CaskError exceptions
+      e.message.concat(" while loading '#{path}'")
+      raise e
+    end
+    begin
+      Cask.const_get(cask_class_name).new
+    rescue CaskError, StandardError, ScriptError => e
+      # bug: e.message.concat doesn't work with CaskError exceptions
+      e.message.concat(" while instantiating '#{cask_class_name}' from '#{path}'")
+      raise e
+    end
   end
 
   def cask_class_name

lib/cask/source/uri.rb

@@ -14,10 +14,12 @@ class Cask::Source::URI
     path = HOMEBREW_CACHE_CASKS.join(File.basename(uri))
     ohai "Downloading #{uri}"
     odebug "Download target -> #{path.to_s}"
-    curl(uri, '-o', path.to_s)
+    begin
+      curl(uri, '-o', path.to_s)
+    rescue ErrorDuringExecution
+      raise CaskUnavailableError.new uri
+    end
     Cask::Source::PathSlashOptional.new(path).load
-  rescue ErrorDuringExecution
-    raise CaskUnavailableError, uri
   end
 
   def to_s