From 4244b248a6458399dcdd4e77ea02fbb91d828875 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Mon, 27 Apr 2020 00:12:06 +0900
Subject: [PATCH] Fix a false positive for `Lint/LiteralAsCondition`

This PR fixes a false positive for `Lint/LiteralAsCondition`
when using `true` literal in `while` and similar cases.

`while true` is a known idiom.

Normally `loop` is used, OTOH `while true` may be selected for
speeding up. Users use these methods depending on use case.
That was introduced as part of RubyKaigi 2019.
https://rubykaigi.org/2019/presentations/ktou.html
---
 CHANGELOG.md                                  |  1 +
 lib/rubocop/cop/lint/literal_as_condition.rb  | 23 ++++++-------
 manual/cops_lint.md                           | 15 +++++----
 .../cop/lint/literal_as_condition_spec.rb     | 32 +++++++++++++++++++
 4 files changed, 51 insertions(+), 20 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c92e5c411bf..67c79cfad1c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@
 * [#7899](https://github.com/rubocop-hq/rubocop/issues/7899): Fix an infinite loop error for `Layout/SpaceAroundOperators` with `Layout/ExtraSpacing` when using `ForceEqualSignAlignment: true`. ([@koic][])
 * [#7885](https://github.com/rubocop-hq/rubocop/issues/7885): Fix `Style/IfUnlessModifier` logic when tabs are used for indentation. ([@jonas054][])
 * [#7909](https://github.com/rubocop-hq/rubocop/pull/7909): Fix a false positive for `Lint/ParenthesesAsGroupedExpression` when using an intended grouped parentheses. ([@koic][])
+* [#7913](https://github.com/rubocop-hq/rubocop/pull/7913): Fix a false positive for `Lint/LiteralAsCondition` when using `true` literal in `while` and similar cases. ([@koic][])
 
 ### Changes
 
diff --git a/lib/rubocop/cop/lint/literal_as_condition.rb b/lib/rubocop/cop/lint/literal_as_condition.rb
index 1ab38d41fdb..f98925dd2ea 100644
--- a/lib/rubocop/cop/lint/literal_as_condition.rb
+++ b/lib/rubocop/cop/lint/literal_as_condition.rb
@@ -10,26 +10,25 @@ module Lint
       # @example
       #
       #   # bad
-      #
       #   if 20
       #     do_something
       #   end
       #
-      # @example
-      #
       #   # bad
-      #
       #   if some_var && true
       #     do_something
       #   end
       #
-      # @example
-      #
       #   # good
-      #
       #   if some_var && some_condition
       #     do_something
       #   end
+      #
+      #   # good
+      #   # When using a boolean value for an infinite loop.
+      #   while true
+      #     break if condition
+      #   end
       class LiteralAsCondition < Cop
         MSG = 'Literal `%<literal>s` appeared as a condition.'
 
@@ -38,20 +37,18 @@ def on_if(node)
         end
 
         def on_while(node)
-          check_for_literal(node)
-        end
+          return if condition(node).true_type?
 
-        def on_while_post(node)
           check_for_literal(node)
         end
+        alias on_while_post on_while
 
         def on_until(node)
-          check_for_literal(node)
-        end
+          return if condition(node).false_type?
 
-        def on_until_post(node)
           check_for_literal(node)
         end
+        alias on_until_post on_until
 
         def on_case(case_node)
           if case_node.condition
diff --git a/manual/cops_lint.md b/manual/cops_lint.md
index 423e8817261..9693297739d 100644
--- a/manual/cops_lint.md
+++ b/manual/cops_lint.md
@@ -993,24 +993,25 @@ if/while/until.
 
 ```ruby
 # bad
-
 if 20
   do_something
 end
-```
-```ruby
-# bad
 
+# bad
 if some_var && true
   do_something
 end
-```
-```ruby
-# good
 
+# good
 if some_var && some_condition
   do_something
 end
+
+# good
+# When using a boolean value for an infinite loop.
+while true
+  break if condition
+end
 ```
 
 ## Lint/LiteralInInterpolation
diff --git a/spec/rubocop/cop/lint/literal_as_condition_spec.rb b/spec/rubocop/cop/lint/literal_as_condition_spec.rb
index 294f61cf32d..225d5f48722 100644
--- a/spec/rubocop/cop/lint/literal_as_condition_spec.rb
+++ b/spec/rubocop/cop/lint/literal_as_condition_spec.rb
@@ -176,4 +176,36 @@
       end
     RUBY
   end
+
+  it 'accepts `true` literal in `while`' do
+    expect_no_offenses(<<~RUBY)
+      while true
+        break if condition
+      end
+    RUBY
+  end
+
+  it 'accepts `true` literal in post-loop `while`' do
+    expect_no_offenses(<<~RUBY)
+      begin
+        break if condition
+      end while true
+    RUBY
+  end
+
+  it 'accepts `false` literal in `until`' do
+    expect_no_offenses(<<~RUBY)
+      until false
+        break if condition
+      end
+    RUBY
+  end
+
+  it 'accepts `false` literal in post-loop `until`' do
+    expect_no_offenses(<<~RUBY)
+      begin
+        break if condition
+      end until false
+    RUBY
+  end
 end