From 61578d9fb2a5d62d68b955d628d30cfc760821d7 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Sun, 6 Sep 2020 02:56:46 +0900
Subject: [PATCH] [Fix #165] Fix a false positive for `Performance/Sum`

Fixes #165.

This PR fixes a false positive for `Performance/Sum`
when using initial value argument is a variable.
---
 CHANGELOG.md                             |  1 +
 lib/rubocop/cop/performance/sum.rb       |  2 +-
 spec/rubocop/cop/performance/sum_spec.rb | 33 ++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 075bdb6470..10af6840ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Bug fixes
 
 * [#164](https://github.com/rubocop-hq/rubocop-performance/pull/164): Fix an error for `Performance/CollectionLiteralInLoop` when a method from `Enumerable` is called with no receiver. ([@eugeneius][])
+* [#165](https://github.com/rubocop-hq/rubocop-performance/issues/165): Fix a false positive for `Performance/Sum` when using initial value argument is a variable. ([@koic][])
 
 ## 1.8.0 (2020-09-04)
 
diff --git a/lib/rubocop/cop/performance/sum.rb b/lib/rubocop/cop/performance/sum.rb
index a1bf307d0c..e3d66c9213 100644
--- a/lib/rubocop/cop/performance/sum.rb
+++ b/lib/rubocop/cop/performance/sum.rb
@@ -98,7 +98,7 @@ def build_good_method(init)
 
           unless init.empty?
             init = init.first
-            good_method += "(#{init.source})" if init.source.to_i != 0
+            good_method += "(#{init.source})" unless init.int_type? && init.value.zero?
           end
           good_method
         end
diff --git a/spec/rubocop/cop/performance/sum_spec.rb b/spec/rubocop/cop/performance/sum_spec.rb
index b0b10f74da..edaf3737c1 100644
--- a/spec/rubocop/cop/performance/sum_spec.rb
+++ b/spec/rubocop/cop/performance/sum_spec.rb
@@ -37,6 +37,39 @@
       RUBY
     end
 
+    it "registers an offense and corrects when using `array.#{method}(0, :+)`" do
+      expect_offense(<<~RUBY, method: method)
+        array.#{method}(0, :+)
+              ^{method}^^^^^^^ Use `sum` instead of `#{method}(0, :+)`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        array.sum
+      RUBY
+    end
+
+    it "registers an offense and corrects when using `array.#{method}(0.0, :+)`" do
+      expect_offense(<<~RUBY, method: method)
+        array.#{method}(0.0, :+)
+              ^{method}^^^^^^^^^ Use `sum(0.0)` instead of `#{method}(0.0, :+)`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        array.sum(0.0)
+      RUBY
+    end
+
+    it "registers an offense and corrects when using `array.#{method}(init, :+)`" do
+      expect_offense(<<~RUBY, method: method)
+        array.#{method}(init, :+)
+              ^{method}^^^^^^^^^^ Use `sum(init)` instead of `#{method}(init, :+)`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        array.sum(init)
+      RUBY
+    end
+
     it 'does not autocorrect when initial value is not provided' do
       expect_offense(<<~RUBY, method: method)
         array.#{method}(:+)