From 896ba88176f5f73c1e4454891726c2369fba0007 Mon Sep 17 00:00:00 2001
From: viralpraxis <iaroslav2k@gmail.com>
Date: Tue, 22 Oct 2024 09:40:15 +0300
Subject: [PATCH] [Fix #475] Add new `Performance/StringBytesize` cop.

---
 changelog/new_string_bytesize_cop.md          |  1 +
 config/default.yml                            |  6 ++
 .../cop/performance/string_bytesize.rb        | 49 +++++++++++
 lib/rubocop/cop/performance_cops.rb           |  1 +
 .../cop/performance/string_bytesize_spec.rb   | 83 +++++++++++++++++++
 5 files changed, 140 insertions(+)
 create mode 100644 changelog/new_string_bytesize_cop.md
 create mode 100644 lib/rubocop/cop/performance/string_bytesize.rb
 create mode 100644 spec/rubocop/cop/performance/string_bytesize_spec.rb

diff --git a/changelog/new_string_bytesize_cop.md b/changelog/new_string_bytesize_cop.md
new file mode 100644
index 0000000000..956fa63f69
--- /dev/null
+++ b/changelog/new_string_bytesize_cop.md
@@ -0,0 +1 @@
+* [#474](https://github.com/rubocop/rubocop-performance/pull/474): Add new `Performance/StringBytesize` cop. ([@viralpraxis][])
diff --git a/config/default.yml b/config/default.yml
index da765ab5c4..f1897d96dc 100644
--- a/config/default.yml
+++ b/config/default.yml
@@ -326,6 +326,12 @@ Performance/StartWith:
   VersionAdded: '0.36'
   VersionChanged: '1.10'
 
+Performance/StringBytesize:
+  Description: "Use `String#bytesize` instead of calculating the size of the bytes array."
+  SafeAutoCorrect: false
+  Enabled: 'pending'
+  VersionAdded: '<<next>>'
+
 Performance/StringIdentifierArgument:
   Description: 'Use symbol identifier argument instead of string identifier argument.'
   Enabled: pending
diff --git a/lib/rubocop/cop/performance/string_bytesize.rb b/lib/rubocop/cop/performance/string_bytesize.rb
new file mode 100644
index 0000000000..ebecc836b4
--- /dev/null
+++ b/lib/rubocop/cop/performance/string_bytesize.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Performance
+      # Checks for calls to `#bytes` counting method and suggests using `bytesize` instead.
+      # The `bytesize` method is more efficient and directly returns the size in bytes,
+      # avoiding the intermediate array allocation that `bytes.size` incurs.
+      #
+      # @safety
+      #   This cop is unsafe because it assumes that the receiver
+      #   responds to `#bytesize` method.
+      #
+      # @example
+      #   # bad
+      #   string_var.bytes.count
+      #   "foobar".bytes.size
+      #
+      #   # good
+      #   string_var.bytesize
+      #   "foobar".bytesize
+      class StringBytesize < Base
+        extend AutoCorrector
+
+        MSG = 'Use `String#bytesize` instead of calculating the size of the bytes array.'
+        RESTRICT_ON_SEND = %i[size length count].freeze
+
+        def_node_matcher :string_bytes_method?, <<~MATCHER
+          (call (call !nil? :bytes) {:size :length :count})
+        MATCHER
+
+        def on_send(node)
+          string_bytes_method?(node) do
+            add_offense(node) do |corrector|
+              corrector.replace(node, replacement(node))
+            end
+          end
+        end
+        alias on_csend on_send
+
+        def replacement(node)
+          receiver = node.receiver
+
+          "#{receiver.receiver.source}#{receiver.loc.dot.source}bytesize"
+        end
+      end
+    end
+  end
+end
diff --git a/lib/rubocop/cop/performance_cops.rb b/lib/rubocop/cop/performance_cops.rb
index 2a18f26120..e71d4066c7 100644
--- a/lib/rubocop/cop/performance_cops.rb
+++ b/lib/rubocop/cop/performance_cops.rb
@@ -44,6 +44,7 @@
 require_relative 'performance/size'
 require_relative 'performance/sort_reverse'
 require_relative 'performance/squeeze'
+require_relative 'performance/string_bytesize'
 require_relative 'performance/start_with'
 require_relative 'performance/string_identifier_argument'
 require_relative 'performance/string_include'
diff --git a/spec/rubocop/cop/performance/string_bytesize_spec.rb b/spec/rubocop/cop/performance/string_bytesize_spec.rb
new file mode 100644
index 0000000000..e3a341af78
--- /dev/null
+++ b/spec/rubocop/cop/performance/string_bytesize_spec.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Performance::StringBytesize, :config do
+  let(:msg) { 'Use `String#bytesize` instead of calculating the size of the bytes array.' }
+
+  it 'registers an offense with `size` method' do
+    expect_offense(<<~RUBY)
+      string.bytes.size
+      ^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      string.bytesize
+    RUBY
+  end
+
+  it 'registers an offense with `length` method' do
+    expect_offense(<<~RUBY)
+      string.bytes.length
+      ^^^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      string.bytesize
+    RUBY
+  end
+
+  it 'registers an offense with `count` method' do
+    expect_offense(<<~RUBY)
+      string.bytes.count
+      ^^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      string.bytesize
+    RUBY
+  end
+
+  it 'registers an offense with string literal' do
+    expect_offense(<<~RUBY)
+      "foobar".bytes.count
+      ^^^^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      "foobar".bytesize
+    RUBY
+  end
+
+  it 'registers an offense and autocorrects with safe navigation' do
+    expect_offense(<<~RUBY)
+      string&.bytes&.count
+      ^^^^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      string&.bytesize
+    RUBY
+  end
+
+  it 'registers an offense and autocorrects with partial safe navigation' do
+    expect_offense(<<~RUBY)
+      string&.bytes.count
+      ^^^^^^^^^^^^^^^^^^^ #{msg}
+    RUBY
+
+    expect_correction(<<~RUBY)
+      string&.bytesize
+    RUBY
+  end
+
+  it 'does not register an offenses without array size method' do
+    expect_no_offenses(<<~RUBY)
+      string.bytes
+    RUBY
+  end
+
+  it 'does not register an offenses with `bytes` without explicit receiver' do
+    expect_no_offenses(<<~RUBY)
+      bytes.size
+    RUBY
+  end
+end