Add max_allowed calls to FeatureEnvy smell detector

This is adding a configuration `max_calls` key for the FeatureEnvy smell detector

Fixes troessner#1535

docs/Feature-Envy.md

@@ -61,7 +61,7 @@ Reek cannot reliably detect that each call's receiver is a different arg and wil
 ```
   [4, 5, 6]:FeatureEnvy: Foo#initialize refers to 'arg' more than self (maybe move it to another class?)
 ```
-  
+
 If you're running into this problem you can disable this smell detector for this method either via
 configuration:
 
@@ -91,3 +91,48 @@ _Feature Envy_ is only triggered if there are some references to self and _[Util
 ## Configuration
 
 _Feature Envy_ supports the [Basic Smell Options](Basic-Smell-Options.md).
+
+Option | Value | Effect
+-------|-------|-------
+`max_calls` |  integer | The maximum number of duplicate calls allowed within a method. Defaults to 3.
+
+
+## Example configuration
+
+### Adjusting `max_calls`
+
+Imagine code like this:
+
+```ruby
+class Alfa
+  def bravo(charlie)
+    (charlie.delta - charlie.echo) * foxtrot
+  end
+end
+```
+
+This would report:
+
+>>
+src.rb -- 1 warnings:
+  [3, 3]:FeatureEnvy: Alfa#bravo refers to 'charlie' more than self (maybe move it to another class?)
+
+If you want to allow those double calls here you can disable it in 2 different ways:
+
+1.) Via source code comment:
+
+```ruby
+class Alfa
+  # :reek:FeatureEnvy { max_calls: 3 }
+  def bravo(charlie)
+    (charlie.delta - charlie.echo) * foxtrot
+  end
+end
+```
+
+2.) Via configuration file:
+
+```yaml
+DuplicateMethodCall:
+  max_calls: 3
+```

docs/defaults.reek.yml

@@ -25,6 +25,7 @@ detectors:
   FeatureEnvy:
     enabled: true
     exclude: []
+    max_calls: 2
   InstanceVariableAssumption:
     enabled: true
     exclude: []

lib/reek/configuration/schema.yml

@@ -47,6 +47,8 @@ mapping:
         type: map
         mapping:
           <<: *detector_base
+          max_calls:
+            type: number
       InstanceVariableAssumption:
         type: map
         mapping:
@@ -203,7 +205,7 @@ mapping:
       =:
         type: map
         mapping: *all_detectors
-        
+
   "exclude_paths":
     type: seq
     sequence:

lib/reek/smell_detectors/feature_envy.rb

@@ -36,6 +36,15 @@ module SmellDetectors
     #
     # See {file:docs/Feature-Envy.md} for details.
     class FeatureEnvy < BaseDetector
+      # The name of the config field that sets the maximum number of
+      # identical calls to be permitted within any single method.
+      MAX_ALLOWED_CALLS_KEY = 'max_calls'
+      DEFAULT_MAX_CALLS = 2
+
+      def self.default_config
+        super.merge(MAX_ALLOWED_CALLS_KEY => DEFAULT_MAX_CALLS)
+      end
+
       #
       # Checks whether the given +context+ includes any code fragment that
       # might "belong" on another class.
@@ -46,7 +55,9 @@ def sniff
         return [] if context.singleton_method? || context.module_function?
         return [] unless context.references_self?
 
-        envious_receivers.map do |name, lines|
+        envious_receivers.select do |_key, lines|
+          lines.length >= max_allowed_calls
+        end.map do |name, lines|
           smell_warning(
             lines: lines,
             message: "refers to '#{name}' more than self (maybe move it to another class?)",
@@ -65,6 +76,10 @@ def envious_receivers
 
         refs.most_popular
       end
+
+      def max_allowed_calls
+        @max_allowed_calls ||= value(MAX_ALLOWED_CALLS_KEY, context)
+      end
     end
   end
 end