Let Performance/StartWith and Performance/EndWith correct Regexp#match and Regexp#=~

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#82](https://github.com/rubocop-hq/rubocop-performance/pull/82): Let `Performance/StartWith` and `Performance/EndWith` correct `Regexp#match?` and `Regexp#=~`. ([@eugeneius][])
+
 ## 1.5.0 (2019-10-01)
 
 ### Bug fixes
@@ -63,3 +67,4 @@
 [@tejasbubane]: https://github.com/tejasbubane
 [@rrosenblum]: https://github.com/rrosenblum
 [@splattael]: https://github.com/splattael
+[@eugeneius]: https://github.com/eugeneius

lib/rubocop/cop/performance/end_with.rb

@@ -9,8 +9,11 @@ module Performance
       # @example
       #   # bad
       #   'abc'.match?(/bc\Z/)
+      #   /bc\Z/.match?('abc')
       #   'abc' =~ /bc\Z/
+      #   /bc\Z/ =~ 'abc'
       #   'abc'.match(/bc\Z/)
+      #   /bc\Z/.match('abc')
       #
       #   # good
       #   'abc'.end_with?('bc')
@@ -21,7 +24,8 @@ class EndWith < Cop
 
         def_node_matcher :redundant_regex?, <<-PATTERN
           {(send $!nil? {:match :=~ :match?} (regexp (str $#literal_at_end?) (regopt)))
-           (send (regexp (str $#literal_at_end?) (regopt)) {:match :=~} $_)}
+           (send (regexp (str $#literal_at_end?) (regopt)) {:match :match?} $_)
+           (match-with-lvasgn (regexp (str $#literal_at_end?) (regopt)) $_)}
         PATTERN
 
         def literal_at_end?(regex_str)
@@ -36,6 +40,7 @@ def on_send(node)
 
           add_offense(node)
         end
+        alias on_match_with_lvasgn on_send
 
         def autocorrect(node)
           redundant_regex?(node) do |receiver, regex_str|

lib/rubocop/cop/performance/start_with.rb

@@ -9,8 +9,11 @@ module Performance
       # @example
       #   # bad
       #   'abc'.match?(/\Aab/)
+      #   /\Aab/.match?('abc')
       #   'abc' =~ /\Aab/
+      #   /\Aab/ =~ 'abc'
       #   'abc'.match(/\Aab/)
+      #   /\Aab/.match('abc')
       #
       #   # good
       #   'abc'.start_with?('ab')
@@ -21,7 +24,8 @@ class StartWith < Cop
 
         def_node_matcher :redundant_regex?, <<-PATTERN
           {(send $!nil? {:match :=~ :match?} (regexp (str $#literal_at_start?) (regopt)))
-           (send (regexp (str $#literal_at_start?) (regopt)) {:match :=~} $_)}
+           (send (regexp (str $#literal_at_start?) (regopt)) {:match :match?} $_)
+           (match-with-lvasgn (regexp (str $#literal_at_start?) (regopt)) $_)}
         PATTERN
 
         def literal_at_start?(regex_str)
@@ -39,6 +43,7 @@ def on_send(node)
 
           add_offense(node)
         end
+        alias on_match_with_lvasgn on_send
 
         def autocorrect(node)
           redundant_regex?(node) do |receiver, regex_str|

manual/cops_performance.md

@@ -301,8 +301,11 @@ would suffice.
 ```ruby
 # bad
 'abc'.match?(/bc\Z/)
+/bc\Z/.match?('abc')
 'abc' =~ /bc\Z/
+/bc\Z/ =~ 'abc'
 'abc'.match(/bc\Z/)
+/bc\Z/.match('abc')
 
 # good
 'abc'.end_with?('bc')
@@ -752,8 +755,11 @@ This cop identifies unnecessary use of a regex where
 ```ruby
 # bad
 'abc'.match?(/\Aab/)
+/\Aab/.match?('abc')
 'abc' =~ /\Aab/
+/\Aab/ =~ 'abc'
 'abc'.match(/\Aab/)
+/\Aab/.match('abc')
 
 # good
 'abc'.start_with?('ab')

spec/rubocop/cop/performance/end_with_spec.rb

@@ -4,68 +4,119 @@
   subject(:cop) { described_class.new }
 
   shared_examples 'different match methods' do |method|
-    it "autocorrects #{method} /abc\\z/" do
+    it "autocorrects str#{method} /abc\\z/" do
       new_source = autocorrect_source("str#{method} /abc\\z/")
       expect(new_source).to eq "str.end_with?('abc')"
     end
 
-    it "autocorrects #{method} /\\n\\z/" do
+    it "autocorrects /abc\\z/#{method} str" do
+      new_source = autocorrect_source("/abc\\z/#{method} str")
+      expect(new_source).to eq "str.end_with?('abc')"
+    end
+
+    it "autocorrects str#{method} /\\n\\z/" do
       new_source = autocorrect_source("str#{method} /\\n\\z/")
       expect(new_source).to eq 'str.end_with?("\n")'
     end
 
-    it "autocorrects #{method} /\\t\\z/" do
+    it "autocorrects /\\n\\z/#{method} str" do
+      new_source = autocorrect_source("/\\n\\z/#{method} str")
+      expect(new_source).to eq 'str.end_with?("\n")'
+    end
+
+    it "autocorrects str#{method} /\\t\\z/" do
       new_source = autocorrect_source("str#{method} /\\t\\z/")
       expect(new_source).to eq 'str.end_with?("\t")'
     end
 
+    it "autocorrects /\\t\\z/#{method} str" do
+      new_source = autocorrect_source("/\\t\\z/#{method} str")
+      expect(new_source).to eq 'str.end_with?("\t")'
+    end
+
+    # regexp metacharacters
     %w[. $ ^ |].each do |str|
-      it "autocorrects #{method} /\\#{str}\\z/" do
+      it "autocorrects str#{method} /\\#{str}\\z/" do
         new_source = autocorrect_source("str#{method} /\\#{str}\\z/")
         expect(new_source).to eq "str.end_with?('#{str}')"
       end
 
-      it "doesn't register an error for #{method} /#{str}\\z/" do
+      it "autocorrects /\\#{str}\\z/#{method} str" do
+        new_source = autocorrect_source("/\\#{str}\\z/#{method} str")
+        expect(new_source).to eq "str.end_with?('#{str}')"
+      end
+
+      it "doesn't register an error for str#{method} /#{str}\\z/" do
         expect_no_offenses("str#{method} /#{str}\\z/")
       end
+
+      it "doesn't register an error for /#{str}\\z/#{method} str" do
+        expect_no_offenses("/#{str}\\z/#{method} str")
+      end
     end
 
     # escapes like "\n"
     # note that "\b" is a literal backspace char in a double-quoted string...
     # but in a regex, it's an anchor on a word boundary
     %w[a e f r t v].each do |str|
-      it "autocorrects #{method} /\\#{str}\\z/" do
+      it "autocorrects str#{method} /\\#{str}\\z/" do
         new_source = autocorrect_source("str#{method} /\\#{str}\\z/")
         expect(new_source).to eq %{str.end_with?("\\#{str}")}
       end
+
+      it "autocorrects /\\#{str}\\z/#{method} str" do
+        new_source = autocorrect_source("/\\#{str}\\z/#{method} str")
+        expect(new_source).to eq %{str.end_with?("\\#{str}")}
+      end
     end
 
     # character classes, anchors
     %w[w W s S d D A Z z G b B h H R X S].each do |str|
-      it "doesn't register an error for #{method} /\\#{str}\\z/" do
+      it "doesn't register an error for str#{method} /\\#{str}\\z/" do
         expect_no_offenses("str#{method} /\\#{str}\\z/")
       end
+
+      it "doesn't register an error for /\\#{str}\\z/#{method} str" do
+        expect_no_offenses("/\\#{str}\\z/#{method} str")
+      end
     end
 
     # characters with no special meaning whatsoever
     %w[i j l m o q y].each do |str|
-      it "autocorrects #{method} /\\#{str}\\z/" do
+      it "autocorrects str#{method} /\\#{str}\\z/" do
         new_source = autocorrect_source("str#{method} /\\#{str}\\z/")
         expect(new_source).to eq "str.end_with?('#{str}')"
       end
+
+      it "autocorrects /\\#{str}\\z/#{method} str" do
+        new_source = autocorrect_source("/\\#{str}\\z/#{method} str")
+        expect(new_source).to eq "str.end_with?('#{str}')"
+      end
     end
 
-    it "formats the error message correctly for #{method} /abc\\z/" do
+    it "formats the error message correctly for str#{method} /abc\\z/" do
       inspect_source("str#{method} /abc\\z/")
       expect(cop.messages).to eq(['Use `String#end_with?` instead of a ' \
                                   'regex match anchored to the end of ' \
                                   'the string.'])
     end
 
-    it "autocorrects #{method} /\\\\\\z/" do
+    it "formats the error message correctly for /abc\\z/#{method} str" do
+      inspect_source("/abc\\z/#{method} str")
+      expect(cop.messages).to eq(['Use `String#end_with?` instead of a ' \
+                                  'regex match anchored to the end of ' \
+                                  'the string.'])
+    end
+
+    it "autocorrects str#{method} /\\\\\\z/" do
       new_source = autocorrect_source("str#{method} /\\\\\\z/")
       expect(new_source).to eq("str.end_with?('\\\\')")
     end
+
+    it "autocorrects /\\\\\\z/#{method} str" do
+      new_source = autocorrect_source("/\\\\\\z/#{method} str")
+      expect(new_source).to eq("str.end_with?('\\\\')")
+    end
   end
 
   include_examples('different match methods', '.match?')

spec/rubocop/cop/performance/start_with_spec.rb

@@ -4,59 +4,99 @@
   subject(:cop) { described_class.new }
 
   shared_examples 'different match methods' do |method|
-    it "autocorrects #{method} /\\Aabc/" do
+    it "autocorrects str#{method} /\\Aabc/" do
       new_source = autocorrect_source("str#{method} /\\Aabc/")
       expect(new_source).to eq "str.start_with?('abc')"
     end
 
+    it "autocorrects /\\Aabc/#{method} str" do
+      new_source = autocorrect_source("/\\Aabc/#{method} str")
+      expect(new_source).to eq "str.start_with?('abc')"
+    end
+
     # escapes like "\n"
     # note that "\b" is a literal backspace char in a double-quoted string...
     # but in a regex, it's an anchor on a word boundary
     %w[a e f r t v].each do |str|
-      it "autocorrects #{method} /\\A\\#{str}/" do
+      it "autocorrects str#{method} /\\A\\#{str}/" do
         new_source = autocorrect_source("str#{method} /\\A\\#{str}/")
         expect(new_source).to eq %{str.start_with?("\\#{str}")}
       end
+
+      it "autocorrects /\\A\\#{str}#{method} str/" do
+        new_source = autocorrect_source("/\\A\\#{str}/#{method} str")
+        expect(new_source).to eq %{str.start_with?("\\#{str}")}
+      end
     end
 
     # regexp metacharacters
     %w[. * ? $ ^ |].each do |str|
-      it "autocorrects #{method} /\\A\\#{str}/" do
+      it "autocorrects str#{method} /\\A\\#{str}/" do
         new_source = autocorrect_source("str#{method} /\\A\\#{str}/")
         expect(new_source).to eq "str.start_with?('#{str}')"
       end
 
-      it "doesn't register an error for #{method} /\\A#{str}/" do
+      it "autocorrects /\\A\\#{str}/#{method} str" do
+        new_source = autocorrect_source("/\\A\\#{str}/#{method} str")
+        expect(new_source).to eq "str.start_with?('#{str}')"
+      end
+
+      it "doesn't register an error for str#{method} /\\A#{str}/" do
         expect_no_offenses("str#{method} /\\A#{str}/")
       end
+
+      it "doesn't register an error for /\\A#{str}/#{method} str" do
+        expect_no_offenses("/\\A#{str}/#{method} str")
+      end
     end
 
     # character classes, anchors
     %w[w W s S d D A Z z G b B h H R X S].each do |str|
-      it "doesn't register an error for #{method} /\\A\\#{str}/" do
+      it "doesn't register an error for str#{method} /\\A\\#{str}/" do
         expect_no_offenses("str#{method} /\\A\\#{str}/")
       end
+
+      it "doesn't register an error for /\\A\\#{str}/#{method} str" do
+        expect_no_offenses("/\\A\\#{str}/#{method} str")
+      end
     end
 
     # characters with no special meaning whatsoever
     %w[i j l m o q y].each do |str|
-      it "autocorrects #{method} /\\A\\#{str}/" do
+      it "autocorrects str#{method} /\\A\\#{str}/" do
         new_source = autocorrect_source("str#{method} /\\A\\#{str}/")
         expect(new_source).to eq "str.start_with?('#{str}')"
       end
+
+      it "autocorrects /\\A\\#{str}#{method} str/" do
+        new_source = autocorrect_source("/\\A\\#{str}/#{method} str")
+        expect(new_source).to eq "str.start_with?('#{str}')"
+      end
     end
 
-    it "formats the error message correctly for #{method} /\\Aabc/" do
+    it "formats the error message correctly for str#{method} /\\Aabc/" do
       inspect_source("str#{method} /\\Aabc/")
       expect(cop.messages).to eq(['Use `String#start_with?` instead of a ' \
                                   'regex match anchored to the beginning of ' \
                                   'the string.'])
     end
 
-    it "autocorrects #{method} /\\A\\\\/" do
+    it "formats the error message correctly for /\\Aabc/#{method} str" do
+      inspect_source("/\\Aabc/#{method} str")
+      expect(cop.messages).to eq(['Use `String#start_with?` instead of a ' \
+                                  'regex match anchored to the beginning of ' \
+                                  'the string.'])
+    end
+
+    it "autocorrects str#{method} /\\A\\\\/" do
       new_source = autocorrect_source("str#{method} /\\A\\\\/")
       expect(new_source).to eq("str.start_with?('\\\\')")
     end
+
+    it "autocorrects /\\A\\\\/#{method} str" do
+      new_source = autocorrect_source("/\\A\\\\/#{method} str")
+      expect(new_source).to eq("str.start_with?('\\\\')")
+    end
   end
 
   include_examples('different match methods', '.match?')