Build out two-fer analyzer

Author: iHiD

lib/analyzers/exercise_analyzer.rb

@@ -1,4 +1,11 @@
 class ExerciseAnalyzer
+
+  # This is just flow-control for quickly exiting the 
+  # analysis. We probably don't want to do things this 
+  # way eventually, but it helps remove noise for now.
+  class FinishedFlowControlException < RuntimeError
+  end
+
   def initialize(code_to_analyze)
     @code_to_analyze = code_to_analyze
     @approve = false
@@ -7,11 +14,13 @@ def initialize(code_to_analyze)
   end
 
   def call
-    analyze!
+    begin
+      analyze!
+    rescue FinishedFlowControlException
+    end
     results
   end
 
-
   def results
     {
       approve: approve,

lib/analyzers/two_fer/analyze.rb

@@ -1,8 +1,275 @@
 module TwoFer
+
+  MESSAGES = {
+    no_module: "No module or class called TwoFer",
+    no_method: "No method called two_fer",
+    splat_args: "Rather than using *%s, how about acutally setting a paramater called 'name'?",
+    missing_default_param: "There is not a correct default param - the tests will fail",
+    incorrect_default_param: "You could set the default value to 'you' to avoid conditionals",
+    string_building: "Rather than using string building, use interpolation",
+    kernel_format: "Rather than using the format method, use interpolation",
+    string_format: "Rather than using string's format/percentage method, use interpolation"
+  }
+
   class Analyze < ExerciseAnalyzer
     include Mandate
 
     def analyze!
+      # Note that all "check_...!" methods exit this method if the solution
+      # is approved or disapproved, so each step is only called if the
+      # previous one has not resolved what to do.
+
+      # Firstly we want to check that the structure of this
+      # solution is correct and that there is nothing structural
+      # stopping it from passing the tests
+      check_structure!
+
+      # Now we want to ensure that the method signature
+      # is sane and that it has valid arguments
+      check_method_signature!
+
+      # There is one optimal solution for two-fer which needs
+      # no commnents and can just be approved. If we have it, then
+      # let's just acknowledge it and get out of here.
+      check_for_optimal_solution!
+
+      # We often see solutions that are correct but use different
+      # string concatenation options (e.g. string#+, String.format, etc)
+      # We'll approve these but want to leave a comment that introduces
+      # them to string interpolation in case they don't know about it.
+      check_for_correct_solution_without_string_interpolaton!
+
+      # The most common error in twofer is people using conditionals
+      # to check where the value passed in is nil, rather than using a defaul
+      # value. We want to check for conditionals and tell the user about the
+      # default paramater if we see one.
+      check_for_conditional_on_default_argument!
+
+      # Sometiems people specify the names (if name == "Alice" ...). If we
+      # do this, suggest using string interpolation to make us of the
+      # paramter, rather than using a conditional on it.
+      # check_for_names!
+
+      # We don't have any idea about this solution, so let's refer it to a
+      # mentor and get exit our analysis.
+      refer_to_mentor!
+    end
+
+    # ###
+    # Analysis functions
+    # ###
+    def check_structure!
+      # First we check that there is a two-fer class or module
+      # and that it contains a method called two-fer
+      disapprove!(:no_module) unless two_fer_module
+      disapprove!(:no_method) unless main_method
+    end
+
+    def check_method_signature!
+      # If there is no parameter or it doesn't have a default value,
+      # then this solution won't pass the tests.
+      disapprove!(:missing_default_param) if paramaters.size != 1
+
+      # If they provide a splat, the tests can pass but we
+      # should suggest they use a real paramater
+      disapprove!(:splat_args, first_paramater_name) if first_paramater.restarg_type?
+
+      # If they don't provide an optional argument the tests will fail
+      disapprove!(:missing_default_param) unless first_paramater.optarg_type?
+    end
+
+    def check_for_optimal_solution!
+      # The optional solution looks like this:
+      #
+      # def self.two_fer(name="you")
+      #   "One for #{name}, one for me."
+      # end
+      # 
+      # The default argument must be 'you', and it must just be a single
+      # statement using interpolation. Other solutions might be approved
+      # but this is the only one that we would approve without comment.
+
+      return unless default_argument_is_optimal?
+      return unless one_line_solution?
+      return unless using_string_interpolation?
+
+      # If the interpolation has more than three components, then they've
+      # done something weird, so let's get a mentor to look at it!
+      refer_to_mentor! unless string_interpolation_has_three_components?
+
+      approve!
+    end
+
+    def check_for_correct_solution_without_string_interpolaton!
+      # If we don't have a correct default argugment or a one line
+      # solution then let's just get out of here.
+      return unless default_argument_is_optimal?
+      return unless one_line_solution?
+
+      loc = first_line_in_method(main_method)
+
+      # In the case of:
+      # "One for " + name + ", one for me."
+      if loc.method_name == :+ &&
+         loc.arguments[0].type == :str
+        approve!(:string_building)
+      end
+
+      # In the case of:
+      # format("One for %s, one for me.", name)
+      if loc.method_name == :format &&
+         loc.receiver == nil &&
+         loc.arguments[0].type == :str &&
+         loc.arguments[1].type == :lvar
+        approve!(:kernel_format)
+      end
+
+      # In the case of:
+      # "One for %s, one for me." % name
+      if loc.method_name == :% &&
+         loc.receiver.type == :str &&
+         loc.arguments[0].type == :lvar
+        approve!(:string_format)
+      end
+
+      # If we have a one-line method that passes the tests, then it's not
+      # soemthing we've planned for, so let's refer it to a mentor
+      return refer_to_mentor!
+    end
+
+    def check_for_conditional_on_default_argument!
+      loc = first_line_in_method(main_method)
+
+      # If we don't have a conditional, then let's get out of here.
+      #
+      # TODO: We might wnt to refactor this to extract a conditional from the
+      # method rather than insist on it being the first line.
+      return unless loc.type == :if
+
+      # Get the clause of the conditional (ie the bit after the "if" keyword)
+      conditional = extract_conditional_clause(loc)
+
+      # Let's warn about using a better default if they `if name == nil`
+      if is_lvar?(conditional.receiver, :name) &&
+         conditional.first_argument == default_argument
+        disapprove!(:incorrect_default_param)
+      end
+
+      # Same thing but if they do it the other way round, ie `if nil == name`
+      if conditional.receiver == default_argument &&
+         is_lvar?(conditional.first_argument, :name)
+        disapprove!(:incorrect_default_param)
+      end
+    end
+
+    # ###
+    # Analysis helpers
+    # ###
+    def default_argument_is_optimal?
+      default_argument_value == "you"
+    end
+
+    def one_line_solution?
+      main_method.body.line_count == 1
+    end
+
+    def using_string_interpolation?
+      main_method.body.dstr_type?
+    end
+
+    def string_interpolation_has_three_components?
+      #main_method.body.pry
+      main_method.body.children.size == 3
+    end
+
+    # ###
+    # Static analysis helpers
+    # ###
+    def num_lines_in_method(method)
+      method.body.child_nodes.size
+    end
+
+    def first_line_in_method(method)
+      # A begin block signifies multiple lines
+      # so we return the first line.
+      method.body.children.first if main_method.body.type == :begin
+
+      # Without a begin block we just have one line,
+      # so we return the method body, which *is* the first line
+      method.body
+    end
+
+    # Is this an lvar (local variable) with a given name?
+    def is_lvar?(node, name)
+      node.lvar_type? && node.children[0] == name
+    end
+
+    def extract_conditional_clause(loc)
+      loc.children[0]
+    end
+
+    memoize
+    def two_fer_module
+      ExtractModuleOrClass.(root_node, "TwoFer")
+    end
+
+    memoize
+    def main_method
+      ExtractClassMethod.(two_fer_module, "two_fer")
+    end
+
+    memoize
+    def paramaters
+      main_method.arguments
+    end
+
+    memoize
+    def first_paramater
+      paramaters.first
+    end
+
+    def first_paramater_name
+      first_paramater.children[0]
+    end
+
+    def default_argument
+      first_paramater.children[1]
+    end
+
+    def default_argument_value
+      default_argument.children[0]
+    end
+
+
+    # ###
+    # Flow helpers
+    #
+    # These are totally generic to all exercises and
+    # can probably be extracted to parent
+    # ###
+    def approve!(msg = nil)
+      self.messages << MESSAGES[msg] if msg
+      self.approve = true
+
+      raise FinishedFlowControlException
+    end
+
+    def refer_to_mentor!
+      self.refer_to_mentor = true
+
+      # Refering to mentor is an explicit
+      # command resulting from weirdness
+      # and should override approving
+      self.approve = false
+
+      raise FinishedFlowControlException
+    end
+
+    def disapprove!(msg, *msg_args)
+      self.messages << (MESSAGES[msg] % msg_args)
+      self.approve = false
+
+      raise FinishedFlowControlException
     end
   end
 end

lib/generic/extract_class_method.rb

@@ -0,0 +1,30 @@
+class ExtractClassMethod < Parser::AST::Processor
+  include Mandate
+
+  def initialize(node_to_search, name)
+    @node_to_search = node_to_search
+    @name = name.to_sym
+    @found_method = nil
+  end
+
+  def call
+    process(node_to_search)
+    found_method
+  end
+
+  def on_sclass(node)
+    # If we're in a class << self context
+    if node.children[0].self_type?
+      @found_method = ExtractInstanceMethod.(node.children[1], name)
+    end
+  end
+
+  def on_defs(node)
+    if node.method_name == name
+      @found_method = node
+    end
+  end
+
+  private
+  attr_reader :node_to_search, :name, :found_method
+end

lib/generic/extract_instance_method.rb

@@ -0,0 +1,23 @@
+class ExtractInstanceMethod < Parser::AST::Processor
+  include Mandate
+
+  def initialize(node_to_search, name)
+    @node_to_search = node_to_search
+    @name = name.to_sym
+    @found_method = nil
+  end
+
+  def call
+    process(node_to_search)
+    found_method
+  end
+
+  def on_def(node)
+    if node.method_name == name
+      @found_method = node
+    end
+  end
+
+  private
+  attr_reader :node_to_search, :name, :found_method
+end

lib/generic/extract_module_or_class.rb

@@ -0,0 +1,32 @@
+class ExtractModuleOrClass < Parser::AST::Processor
+  include Mandate
+
+  def initialize(node_to_search, name)
+    @node_to_search = node_to_search
+    @name = name
+    @found_constant = nil
+  end
+
+  def call
+    process(node_to_search)
+    found_constant
+  end
+
+  def on_module(node)
+    inspect_node(node)
+  end
+
+  def on_class(node)
+    inspect_node(node)
+  end
+
+  private
+  attr_reader :node_to_search, :name, :found_constant
+
+  def inspect_node(node)
+    if node.children.first.const_name == name
+      @found_constant = node
+    end
+  end
+end
+