Be more careful exception handling in Readline [Fixes #632, #605]

Firstly wrap the entire completion_proc in a begin/rescue/end so that
even if something we're not expecting goes wrong, we don't fail.

Secondly, only throw the user out of pry if reading from readline fails
five times in a row. This avoids a transient error (like a time-out, or
a failed tab completion) from kicking you out of pry; but also avoids
the infinite looping problem that can happen if the error is not transient.

lib/pry/completion.rb

@@ -43,6 +43,7 @@ class Pry
     # @param [Array<String>] commands The array of Pry commands.
     def self.build_completion_proc(target, commands=[""])
       proc do |input|
+        begin
           bind = target
 
           case input
@@ -92,12 +93,8 @@ class Pry
             # Constant or class methods
             receiver = $1
             message = Regexp.quote($2)
-          begin
             candidates = eval("#{receiver}.constants.collect{|m| m.to_s}", bind)
             candidates |= eval("#{receiver}.methods.collect{|m| m.to_s}", bind)
-          rescue RescuableException
-            candidates = []
-          end
             candidates.grep(/^#{message}/).collect{|e| receiver + "::" + e}
 
           when /^(:[^:.]+)\.([^.]*)$/
@@ -113,11 +110,7 @@ class Pry
             receiver = $1
             message = Regexp.quote($5)
 
-          begin
             candidates = eval(receiver, bind).methods.collect{|m| m.to_s}
-          rescue RescuableException
-            candidates = []
-          end
             select_message(receiver, message, candidates)
 
           when /^(-?0x[0-9a-fA-F_]+)\.([^.]*)$/
@@ -125,11 +118,7 @@ class Pry
             receiver = $1
             message = Regexp.quote($2)
 
-          begin
             candidates = eval(receiver, bind).methods.collect{|m| m.to_s}
-          rescue RescuableException
-            candidates = []
-          end
             select_message(receiver, message, candidates)
 
           when /^(\$[^.]*)$/
@@ -148,20 +137,12 @@ class Pry
             if (gv | lv | cv).include?(receiver) or /^[A-Z]/ =~ receiver && /\./ !~ receiver
               # foo.func and foo is local var. OR
               # Foo::Bar.func
-            begin
               candidates = eval("#{receiver}.methods", bind).collect{|m| m.to_s}
-            rescue RescuableException
-              candidates = []
-            end
             else
               # func1.func2
               candidates = []
               ObjectSpace.each_object(Module){|m|
-              begin
                 name = m.name.to_s
-              rescue RescuableException
-                name = ""
-              end
                 next if name != "IRB::Context" and
                 /^(IRB|SLex|RubyLex|RubyToken)/ =~ name
 
@@ -198,6 +179,9 @@ class Pry
 
             (candidates|ReservedWords|commands).grep(/^#{Regexp.quote(input)}/)
           end
+        rescue RescuableException
+          []
+        end
       end
     end
 

lib/pry/pry_instance.rb

@@ -539,6 +539,7 @@ class Pry
   # Manage switching of input objects on encountering EOFErrors
   def handle_read_errors
     should_retry = true
+    exception_count = 0
     begin
       yield
     rescue EOFError
@@ -565,6 +566,11 @@ class Pry
     # anything about it.
     rescue RescuableException => e
       puts "Error: #{e.message}"
+      output.puts e.backtrace
+      exception_count += 1
+      if exception_count < 5
+        retry
+      end
       puts "FATAL: Pry failed to get user input using `#{input}`."
       puts "To fix this you may be able to pass input and output file descriptors to pry directly. e.g."
       puts "  Pry.config.input = STDIN"