Add cop enforcing maximum filename length rule

rubocop/cop/filename_length.rb

+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    class FilenameLength < Cop
+      include RangeHelp
+
+      FILEPATH_MAX_BYTES = 256
+      FILENAME_MAX_BYTES = 100
+      MSG_FILEPATH_LEN = "This file path is too long. It should be #{FILEPATH_MAX_BYTES} or less"
+      MSG_FILENAME_LEN = "This file name is too long. It should be #{FILENAME_MAX_BYTES} or less"
+
+      def investigate(processed_source)
+        file_path = processed_source.file_path
+        return if config.file_to_exclude?(file_path)
+
+        if file_path.bytesize > FILEPATH_MAX_BYTES
+          add_offense(nil, location: source_range(processed_source.buffer, 1, 0, 1), message: MSG_FILEPATH_LEN)
+        elsif File.basename(file_path).bytesize > FILENAME_MAX_BYTES
+          add_offense(nil, location: source_range(processed_source.buffer, 1, 0, 1), message: MSG_FILENAME_LEN)
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/filename_length_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../rubocop/cop/filename_length'
+require_relative '../../support/helpers/expect_offense'
+
+describe RuboCop::Cop::FilenameLength do
+  subject(:cop) { described_class.new }
+
+  it 'does not flag files with names 100 characters long' do
+    expect_no_offenses('puts "it does not matter"', 'a' * 100)
+  end
+
+  it 'tags files with names 101 characters long' do
+    filename = 'a' * 101
+
+    expect_offense(<<~SOURCE, filename)
+    source code
+    ^ This file name is too long. It should be 100 or less
+    SOURCE
+  end
+
+  it 'tags files with names 256 characters long' do
+    filename = 'a' * 256
+
+    expect_offense(<<~SOURCE, filename)
+    source code
+    ^ This file name is too long. It should be 100 or less
+    SOURCE
+  end
+
+  it 'tags files with filepath 256 characters long' do
+    filepath = File.join 'a', 'b' * 254
+
+    expect_offense(<<~SOURCE, filepath)
+    source code
+    ^ This file name is too long. It should be 100 or less
+    SOURCE
+  end
+
+  it 'tags files with filepath 257 characters long' do
+    filepath = File.join 'a', 'b' * 255
+
+    expect_offense(<<~SOURCE, filepath)
+    source code
+    ^ This file path is too long. It should be 256 or less
+    SOURCE
+  end
+end