Validate conditional expressions

Author: nixme

lib/pry-debugger/breakpoints.rb

@@ -11,12 +11,16 @@ module Breakpoints
     # Add a new breakpoint.
     def add(file, line, expression = nil)
       raise ArgumentError, 'Invalid file!' unless File.exist?(file)
+      validate_expression expression
+
       Pry.processor.debugging = true
       Debugger.add_breakpoint(File.expand_path(file), line, expression)
     end
 
     # Change the conditional expression for a breakpoint.
     def change(id, expression = nil)
+      validate_expression expression
+
       breakpoint = find_by_id(id)
       breakpoint.expr = expression
       breakpoint
@@ -79,5 +83,10 @@ def change_status(id, enabled = true)
       breakpoint.enabled = enabled
       breakpoint
     end
+
+    def validate_expression(expression)
+      # `complete_expression?` throws a SyntaxError on invalid input.
+      expression && Pry::Code.complete_expression?(expression)
+    end
   end
 end