formulary: handle ScriptError in formula

I added a new `FormulaUnreadableError` subclass of
`FormulaUnavailableError` so existing `rescue`s of
`FormulaUnavailableError` handle this as well.

The new subclass will output the name of the formula with the error
(because this isn't always obvious from the original exception message)
followed by the original error message.

Fixes #1927.

1 files changed, 13 insertions, 0 deletions

diff --git a/Library/Homebrew/exceptions.rb b/Library/Homebrew/exceptions.rb
index c5d888d64..77da4489e 100644
--- a/Library/Homebrew/exceptions.rb
+++ b/Library/Homebrew/exceptions.rb
@@ -131,6 +131,19 @@ class FormulaClassUnavailableError < FormulaUnavailableError
   end
 end
 
+class FormulaUnreadableError < FormulaUnavailableError
+  attr_reader :formula_error
+
+  def initialize(name, error)
+    super(name)
+    @formula_error = error
+  end
+
+  def to_s
+    "#{name}: " + formula_error.to_s
+  end
+end
+
 class TapFormulaAmbiguityError < RuntimeError
   attr_reader :name, :paths, :formulae