Create Style/FileTouch cop

lovro-bikic · bbatsov · commit 77f3e6fbf595 · 2024-11-26T14:17:49.000+02:00
diff --git a/changelog/new_add_style_touch_file_cop.md b/changelog/new_add_style_touch_file_cop.md
@@ -0,0 +1 @@
+* [#13484](https://github.com/rubocop/rubocop/pull/13484): Add new `Style/FileTouch` cop. ([@lovro-bikic][])
diff --git a/config/default.yml b/config/default.yml
@@ -3959,6 +3959,12 @@ Style/FileRead:
   Enabled: pending
   VersionAdded: '1.24'
 
+Style/FileTouch:
+  Description: 'Favor `FileUtils.touch` for touching files.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+  SafeAutoCorrect: false
+
 Style/FileWrite:
   Description: 'Favor `File.(bin)write` convenience methods.'
   StyleGuide: '#file-write'
diff --git a/lib/rubocop.rb b/lib/rubocop.rb
@@ -542,6 +542,7 @@
 require_relative 'rubocop/cop/style/file_empty'
 require_relative 'rubocop/cop/style/file_null'
 require_relative 'rubocop/cop/style/file_read'
+require_relative 'rubocop/cop/style/file_touch'
 require_relative 'rubocop/cop/style/file_write'
 require_relative 'rubocop/cop/style/float_division'
 require_relative 'rubocop/cop/style/for'
diff --git a/lib/rubocop/cop/style/file_touch.rb b/lib/rubocop/cop/style/file_touch.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # Checks for usage of `File.open` in append mode with empty block.
+      #
+      # Such a usage only creates a new file, but it doesn't update
+      # timestamps for an existing file, which might have been the intention.
+      #
+      # For example, for an existing file `foo.txt`:
+      #
+      #   ruby -e "puts File.mtime('foo.txt')"
+      #   # 2024-11-26 12:17:23 +0100
+      #
+      #   ruby -e "File.open('foo.txt', 'a') {}"
+      #
+      #   ruby -e "puts File.mtime('foo.txt')"
+      #   # 2024-11-26 12:17:23 +0100 -> unchanged
+      #
+      # If the intention was to update timestamps, `FileUtils.touch('foo.txt')`
+      # should be used instead.
+      #
+      # @safety
+      #   Autocorrection is unsafe for this cop because unlike `File.open`,
+      #   `FileUtils.touch` updates an existing file's timestamps.
+      #
+      # @example
+      #   # bad
+      #   File.open(filename, 'a') {}
+      #   File.open(filename, 'a+') {}
+      #
+      #   # good
+      #   FileUtils.touch(filename)
+      #
+      class FileTouch < Base
+        extend AutoCorrector
+
+        MSG = 'Use `FileUtils.touch(%<argument>s)` instead of `File.open` in ' \
+              'append mode with empty block.'
+
+        RESTRICT_ON_SEND = %i[open].freeze
+
+        APPEND_FILE_MODES = %w[a a+ ab a+b at a+t].to_set.freeze
+
+        # @!method file_open?(node)
+        def_node_matcher :file_open?, <<~PATTERN
+          (send
+            (const {nil? cbase} :File) :open
+            $(...)
+            (str %APPEND_FILE_MODES))
+        PATTERN
+
+        def on_send(node)
+          filename = file_open?(node)
+          parent = node.parent
+
+          return unless filename
+          return unless parent && empty_block?(parent)
+
+          message = format(MSG, argument: filename.source)
+          add_offense(parent, message: message) do |corrector|
+            corrector.replace(parent, "FileUtils.touch(#{filename.source})")
+          end
+        end
+
+        private
+
+        def empty_block?(node)
+          node.block_type? && !node.body
+        end
+      end
+    end
+  end
+end
diff --git a/spec/rubocop/cop/style/file_touch_spec.rb b/spec/rubocop/cop/style/file_touch_spec.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Style::FileTouch, :config do
+  it 'registers an offense when using `File.open` in append mode with empty block' do
+    expect_offense(<<~RUBY)
+      File.open(filename, 'a') {}
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `FileUtils.touch(filename)` instead of `File.open` in append mode with empty block.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      FileUtils.touch(filename)
+    RUBY
+  end
+
+  it 'does not register an offense when using `File.open` in append mode without a block' do
+    expect_no_offenses(<<~RUBY)
+      File.open(filename, 'a')
+    RUBY
+  end
+
+  it 'does not register an offense when using `File.open` in write mode' do
+    expect_no_offenses(<<~RUBY)
+      File.open(filename, 'w') {}
+    RUBY
+  end
+
+  it 'does not register an offense when using `File.open` without an access mode' do
+    expect_no_offenses(<<~RUBY)
+      File.open(filename) {}
+    RUBY
+  end
+end

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+* [#13484](https://github.com/rubocop/rubocop/pull/13484): Add new `Style/FileTouch` cop. ([@lovro-bikic][])