From 0400bba5ac9d88b99130b50169040f92c8ed2f7e Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Wed, 16 Jun 2021 02:47:54 +0900
Subject: [PATCH] Fix a false positive for `Style/RegexpLiteral`

This PR fixes the following false positive for `Style/RegexpLiteral`
when using a regexp starts with a blank as a method argument.

```console
% cat example.rb
do_something %r| regexp|

% bundle exec rubocop --only Style/RegexpLiteral -a
(snip)

Offenses:

example.rb:1:14: C: [Corrected] Style/RegexpLiteral: Use // around regular expression.
do_something %r| regexp|
             ^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected

% cat example.rb
do_something / regexp/

% ruby -c example.rb
example.rb:1: syntax error, unexpected end-of-input
```
---
 ...false_positive_for_style_regexp_literal.md |  1 +
 lib/rubocop/cop/style/regexp_literal.rb       |  5 ++-
 spec/rubocop/cop/style/regexp_literal_spec.rb | 38 +++++++++++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 changelog/fix_a_false_positive_for_style_regexp_literal.md

diff --git a/changelog/fix_a_false_positive_for_style_regexp_literal.md b/changelog/fix_a_false_positive_for_style_regexp_literal.md
new file mode 100644
index 00000000000..24ea80f6cc8
--- /dev/null
+++ b/changelog/fix_a_false_positive_for_style_regexp_literal.md
@@ -0,0 +1 @@
+* [#9880](https://github.com/rubocop/rubocop/pull/9880): Fix a false positive for `Style/RegexpLiteral` when using a regexp starts with a blank as a method argument. ([@koic][])
diff --git a/lib/rubocop/cop/style/regexp_literal.rb b/lib/rubocop/cop/style/regexp_literal.rb
index cffea6d3561..13bd1bb06ac 100644
--- a/lib/rubocop/cop/style/regexp_literal.rb
+++ b/lib/rubocop/cop/style/regexp_literal.rb
@@ -117,7 +117,7 @@ def allowed_mixed_slash?(node)
         def allowed_percent_r_literal?(node)
           style == :slashes && contains_disallowed_slash?(node) ||
             style == :percent_r ||
-            allowed_mixed_percent_r?(node) || omit_parentheses_style?(node)
+            allowed_mixed_percent_r?(node) || allowed_omit_parentheses_with_percent_r_literal?(node)
         end
 
         def allowed_mixed_percent_r?(node)
@@ -149,8 +149,9 @@ def preferred_delimiters
           config.for_cop('Style/PercentLiteralDelimiters') ['PreferredDelimiters']['%r'].chars
         end
 
-        def omit_parentheses_style?(node)
+        def allowed_omit_parentheses_with_percent_r_literal?(node)
           return false unless node.parent&.call_type?
+          return true if node.content.start_with?(' ')
 
           enforced_style = config.for_cop('Style/MethodCallWithArgsParentheses')['EnforcedStyle']
 
diff --git a/spec/rubocop/cop/style/regexp_literal_spec.rb b/spec/rubocop/cop/style/regexp_literal_spec.rb
index 5c4affe6c34..77c3178c1ee 100644
--- a/spec/rubocop/cop/style/regexp_literal_spec.rb
+++ b/spec/rubocop/cop/style/regexp_literal_spec.rb
@@ -518,6 +518,25 @@
           ^^^^^^^^^^ Use `//` around regular expression.
         RUBY
       end
+
+      it 'does not register an offense when using a regexp starts with a blank as a method argument' do
+        expect_no_offenses(<<~RUBY)
+          do_something %r/ regexp/
+        RUBY
+      end
+
+      it 'does not register an offense when using a regexp starts with a blank as a safe navigation method argument' do
+        expect_no_offenses(<<~RUBY)
+          foo&.do_something %r/ regexp/
+        RUBY
+      end
+
+      it 'registers an offense when using a regexp starts with a blank' do
+        expect_offense(<<~RUBY)
+          %r/ regexp/
+          ^^^^^^^^^^^ Use `//` around regular expression.
+        RUBY
+      end
     end
 
     context 'when using `%r` regexp with `EnforcedStyle: mixed`' do
@@ -543,6 +562,25 @@
           ^^^^^^^^^^ Use `//` around regular expression.
         RUBY
       end
+
+      it 'does not register an offense when using a regexp starts with a blank as a method argument' do
+        expect_no_offenses(<<~RUBY)
+          do_something %r/ regexp/
+        RUBY
+      end
+
+      it 'does not register an offense when using a regexp starts with a blank as a safe navigation method argument' do
+        expect_no_offenses(<<~RUBY)
+          foo&.do_something %r/ regexp/
+        RUBY
+      end
+
+      it 'registers an offense when using a regexp starts with a blank' do
+        expect_offense(<<~RUBY)
+          %r/ regexp/
+          ^^^^^^^^^^^ Use `//` around regular expression.
+        RUBY
+      end
     end
   end