[rubocop#1611] Add MissingElse cop

CHANGELOG.md

@@ -7,6 +7,7 @@
 * [#1641](https://github.com/bbatsov/rubocop/pull/1641): Add ruby19_no_mixed_keys style to `HashStyle` cop. ([@iainbeeston][])
 * [#1604](https://github.com/bbatsov/rubocop/issues/1604): Add `IgnoreClassMethods` option to `TrivialAccessors` cop. ([@bbatsov][])
 * [#1651](https://github.com/bbatsov/rubocop/issues/1651): The `Style/SpaceAroundOperators` cop now also detects extra spaces around operators. A list of operators that *may* be surrounded by multiple spaces is configurable. ([@bquorning][])
+* [#1611](https://github.com/bbatsov/rubocop/issues/1611): Add new `MissingElse` cop. Default is to have this cop be disabled. ([@rrosenblum][])
 
 ## 0.29.1 (13/02/2015)
 

config/disabled.yml

@@ -19,6 +19,15 @@ Style/MethodCalledOnDoEndBlock:
   StyleGuide: 'https://github.com/bbatsov/ruby-style-guide#single-line-blocks'
   Enabled: false
 
+Style/MissingElse:
+  Description: >-
+                Require if statements to have an else condition.
+                If enabled, it is recommended that
+                Style/UnlessElse and Style/EmptyElse be enabled.
+                This will conflict with Style/EmptyElse if
+                Style/EmptyElse is configured to both
+  Enabled: false
+
 Style/SymbolArray:
   Description: 'Use %i or %I for arrays of symbols.'
   StyleGuide: 'https://github.com/bbatsov/ruby-style-guide#percent-i'

lib/rubocop.rb

@@ -151,6 +151,7 @@
 require 'rubocop/cop/style/each_with_object'
 require 'rubocop/cop/style/else_alignment'
 require 'rubocop/cop/style/empty_else'
+require 'rubocop/cop/style/missing_else'
 require 'rubocop/cop/style/empty_line_between_defs'
 require 'rubocop/cop/style/empty_lines'
 require 'rubocop/cop/style/empty_lines_around_access_modifier'

lib/rubocop/cop/style/missing_else.rb

@@ -0,0 +1,45 @@
+# encoding: utf-8
+
+module RuboCop
+  module Cop
+    module Style
+      # Checks for `if` statements that do not have an `else` statement.
+      class MissingElse < Cop
+        include OnNormalIfUnless
+
+        MSG = '`if` condition requires an `else`-clause.'
+        MSG_NIL = '`if` condition requires an `else`-clause with `nil` in it.'
+        MSG_EMPTY = '`if` condition requires an empty `else`-clause.'
+
+        def on_normal_if_unless(node)
+          unless_else_cop = config.for_cop('Style/UnlessElse')
+          unless_else_enabled = unless_else_cop['Enabled'] if unless_else_cop
+          return if unless_else_enabled &&
+                    node.loc.keyword &&
+                    node.loc.keyword.is?('unless')
+          check(node, if_else_clause(node))
+        end
+
+        def on_case(node)
+          check(node, case_else_clause(node))
+        end
+
+        private
+
+        def check(node, _else_clause)
+          return if node.loc.else
+          empty_else = config.for_cop('Style/EmptyElse')
+          if empty_else && empty_else['Enabled']
+            case empty_else['EnforcedStyle']
+            when 'empty'
+              add_offense(node, node.location, MSG_NIL)
+            when 'nil'
+              add_offense(node, node.location, MSG_EMPTY)
+            end
+          end
+          add_offense(node, node.location, MSG)
+        end
+      end
+    end
+  end
+end