rbinstall.rb: syntax error in gemspec

* tool/rbinstall.rb (load_gemspec): do not hide syntax errors in
  a gemspec file.  check if the result instead.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66460 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/rbinstall.rb

@@ -743,13 +743,10 @@ def load_gemspec(file)
   file = File.realpath(file)
   code = File.read(file, encoding: "utf-8:-")
   code.gsub!(/`git.*?`/m, '""')
-  begin
+  spec = eval(code, binding, file)
-    spec = eval(code, binding, file)
+  unless Gem::Specification === spec
-  rescue SignalException, SystemExit
+    raise TypeError, "[#{file}] isn't a Gem::Specification (#{spec.class} instead)."
-    raise
-  rescue SyntaxError, Exception
   end
-  raise("invalid spec in #{file}") unless spec
   spec.loaded_from = file
   spec
 end