Fix a false negative for Performance/RegexpMatch

Follow up rubocop/rubocop#5569.

This PR fixes a false negative for `Performance/RegexpMatch`
when `MatchData` is not detected in `if` branch of guard condition.

```console
% cat example.rb
# frozen_string_literal: true

raise unless ex.message =~ /can't modify frozen IOError/

% bundle exec rubocop --only Performance/RegexpMatch
Inspecting 1 file
.

1 file inspected, no offenses detected
```

This issue was detected by the following code.
https://github.com/rails/rails/blob/v6.0.0.rc2/actioncable/test/client_test.rb#L94

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2019-07-20 09:00:25 +0900 using RuboCop version 0.72.0.
+# on 2019-07-27 17:51:55 +0800 using RuboCop version 0.73.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -15,16 +15,16 @@ InternalAffairs/NodeDestructuring:
     - 'lib/rubocop/cop/performance/regexp_match.rb'
     - 'lib/rubocop/cop/performance/string_replacement.rb'
 
-# Offense count: 7
+# Offense count: 8
 Metrics/AbcSize:
   Max: 17
 
 # Offense count: 2
 # Configuration parameters: CountComments.
 Metrics/ClassLength:
-  Max: 149
+  Max: 156
 
-# Offense count: 14
+# Offense count: 15
 # Configuration parameters: CountComments, ExcludedMethods.
 Metrics/MethodLength:
   Max: 14

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Bug fixes
 
 * [#67](https://github.com/rubocop-hq/rubocop-performance/issues/67): Fix an error for `Performance/RedundantMerge` when `MaxKeyValuePairs` option is set to `null`. ([@koic][])
+* [#73](https://github.com/rubocop-hq/rubocop-performance/pull/73): Fix a false negative for `Performance/RegexpMatch` when `MatchData` is not detected in `if` branch of guard condition. ([@koic][])
 
 ## 1.4.0 (2019-06-20)
 

lib/rubocop/cop/performance/regexp_match.rb

@@ -177,15 +177,23 @@ def last_match_used?(match_node)
           scope_root = scope_root(match_node)
           body = scope_root ? scope_body(scope_root) : match_node.ancestors.last
 
-          return true if match_node.parent.if_type? &&
-                         match_node.parent.modifier_form?
+          range =
+            if match_node.parent.if_type? && match_node.parent.modifier_form?
+              if_branch_range(match_node)
+            else
+              match_node_pos = match_node.loc.expression.begin_pos
+              next_match_pos = next_match_pos(body, match_node_pos, scope_root)
+
+              match_node_pos..next_match_pos
+            end
 
-          match_node_pos = match_node.loc.expression.begin_pos
+          find_last_match(body, range, scope_root)
+        end
 
-          next_match_pos = next_match_pos(body, match_node_pos, scope_root)
-          range = match_node_pos..next_match_pos
+        def if_branch_range(match_node)
+          expression = match_node.parent.if_branch.loc.expression
 
-          find_last_match(body, range, scope_root)
+          expression.begin_pos..expression.end_pos
         end
 
         def next_match_pos(body, match_node_pos, scope_root)

spec/rubocop/cop/performance/regexp_match_spec.rb

@@ -38,6 +38,18 @@
       end
     RUBY2
 
+    include_examples 'offense', "#{name} in if condition", <<-RUBY, <<-RUBY2
+      do_something if #{cond}
+    RUBY
+      do_something if #{correction}
+    RUBY2
+
+    include_examples 'offense', "#{name} in unless condition", <<-RUBY, <<-RUBY2
+      do_something unless #{cond}
+    RUBY
+      do_something unless #{correction}
+    RUBY2
+
     include_examples 'offense', "#{name} in elsif condition", <<-RUBY, <<-RUBY2
       if cond
         do_something