From 1e59fe1fd0d57314e9003ce3f7c75b05167fb594 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Mon, 22 Jun 2020 12:55:03 +0900
Subject: [PATCH] [Fix #8185] Fix a false positive for `Style/YodaCondition`

Fixes #8185.

This PR fixes a false positive for `Style/YodaCondition` when
interpolation is used on the left side.

String interpolation (and Regexp interpolation) contains variables,
I think it's acceptable to use it on the left hand side.
---
 CHANGELOG.md                                  |  1 +
 docs/modules/ROOT/pages/cops_style.adoc       |  2 ++
 lib/rubocop/cop/style/yoda_condition.rb       | 19 ++++++++++++++++++-
 spec/rubocop/cop/style/yoda_condition_spec.rb |  2 ++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f7d5e5beec6..e3f95a95703 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 * [#8098](https://github.com/rubocop-hq/rubocop/issues/8098): Fix a false positive for `Style/RedundantRegexpCharacterClass` when using interpolations. ([@owst][])
 * [#8150](https://github.com/rubocop-hq/rubocop/pull/8150): Fix a false positive for `Layout/EmptyLinesAroundAttributeAccessor` when using attribute accessors in `if` ... `else` branches. ([@koic][])
 * [#8179](https://github.com/rubocop-hq/rubocop/issues/8179): Fix an infinite correction loop error for `Layout/MultilineBlockLayout` when missing newline before opening parenthesis `(` for block body. ([@koic][])
+* [#8185](https://github.com/rubocop-hq/rubocop/issues/8185): Fix a false positive for `Style/YodaCondition` when interpolation is used on the left hand side. ([@koic][])
 
 ### Changes
 
diff --git a/docs/modules/ROOT/pages/cops_style.adoc b/docs/modules/ROOT/pages/cops_style.adoc
index b7b912312e9..19b2a2fc606 100644
--- a/docs/modules/ROOT/pages/cops_style.adoc
+++ b/docs/modules/ROOT/pages/cops_style.adoc
@@ -10018,6 +10018,8 @@ foo == 99
 foo == "bar"
 foo <= 42
 bar > 10
+"#{interpolation}" == foo
+/#{interpolation}/ == foo
 ----
 
 ==== EnforcedStyle: forbid_for_equality_operators_only
diff --git a/lib/rubocop/cop/style/yoda_condition.rb b/lib/rubocop/cop/style/yoda_condition.rb
index 00640b05a01..cbd4b0f0cb1 100644
--- a/lib/rubocop/cop/style/yoda_condition.rb
+++ b/lib/rubocop/cop/style/yoda_condition.rb
@@ -19,6 +19,8 @@ module Style
       #   foo == "bar"
       #   foo <= 42
       #   bar > 10
+      #   "#{interpolation}" == foo
+      #   /#{interpolation}/ == foo
       #
       # @example EnforcedStyle: forbid_for_equality_operators_only
       #   # bad
@@ -109,7 +111,8 @@ def valid_yoda?(node)
           rhs = node.first_argument
 
           return true if lhs.literal? && rhs.literal? ||
-                         !lhs.literal? && !rhs.literal?
+                         !lhs.literal? && !rhs.literal? ||
+                         interpolation?(lhs)
 
           enforce_yoda? ? lhs.literal? : rhs.literal?
         end
@@ -150,6 +153,20 @@ def source_file_path_constant?(node)
         def program_name?(name)
           PROGRAM_NAMES.include?(name)
         end
+
+        def interpolation?(node)
+          return true if node.dstr_type?
+
+          # TODO: Use `RegexpNode#interpolation?` when the following is released.
+          # https://github.com/rubocop-hq/rubocop-ast/pull/18
+          if node.regexp_type?
+            return true if node.children.any? do |child|
+              child.respond_to?(:begin_type?) && child.begin_type?
+            end
+          end
+
+          false
+        end
       end
     end
   end
diff --git a/spec/rubocop/cop/style/yoda_condition_spec.rb b/spec/rubocop/cop/style/yoda_condition_spec.rb
index c41a9dbbe2f..60f276b0294 100644
--- a/spec/rubocop/cop/style/yoda_condition_spec.rb
+++ b/spec/rubocop/cop/style/yoda_condition_spec.rb
@@ -44,6 +44,8 @@
     it_behaves_like 'accepts', 'b = 1; b == 2'
     it_behaves_like 'accepts', '$var == 5'
     it_behaves_like 'accepts', 'foo == "bar"'
+    it_behaves_like 'accepts', '"#{interpolation}" == foo'
+    it_behaves_like 'accepts', '/#{interpolation}/ == foo'
     it_behaves_like 'accepts', 'foo[0] > "bar" || baz != "baz"'
     it_behaves_like 'accepts', 'node = last_node.parent'
     it_behaves_like 'accepts', '(first_line - second_line) > 0'