Add new Lint/DuplicateRequire cop

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#8474](https://github.com/rubocop-hq/rubocop/pull/8474): Add new `Lint/DuplicateRequire` cop. ([@fatkodima][])
+
 ### Changes
 
 * [#8362](https://github.com/rubocop-hq/rubocop/issues/8362): Add numbers of correctable offenses to summary. ([@nguyenquangminh0711][])

config/default.yml

@@ -1427,6 +1427,11 @@ Lint/DuplicateMethods:
   Enabled: true
   VersionAdded: '0.29'
 
+Lint/DuplicateRequire:
+  Description: 'Check for duplicate `require`s and `require_relative`s.'
+  Enabled: pending
+  VersionAdded: '0.90'
+
 Lint/DuplicateRescueException:
   Description: 'Checks that there are no repeated exceptions used in `rescue` expressions.'
   Enabled: pending

docs/modules/ROOT/pages/cops.adoc

@@ -197,6 +197,7 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#lintduplicateelsifcondition[Lint/DuplicateElsifCondition]
 * xref:cops_lint.adoc#lintduplicatehashkey[Lint/DuplicateHashKey]
 * xref:cops_lint.adoc#lintduplicatemethods[Lint/DuplicateMethods]
+* xref:cops_lint.adoc#lintduplicaterequire[Lint/DuplicateRequire]
 * xref:cops_lint.adoc#lintduplicaterescueexception[Lint/DuplicateRescueException]
 * xref:cops_lint.adoc#linteachwithobjectargument[Lint/EachWithObjectArgument]
 * xref:cops_lint.adoc#lintelselayout[Lint/ElseLayout]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -779,6 +779,34 @@ end
 alias bar foo
 ----
 
+== Lint/DuplicateRequire
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| No
+| 0.90
+| -
+|===
+
+This cop checks for duplicate `require`s and `require_relative`s.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+require 'foo'
+require 'bar'
+require 'foo'
+
+# good
+require 'foo'
+require 'bar'
+----
+
 == Lint/DuplicateRescueException
 
 |===

lib/rubocop.rb

@@ -255,6 +255,7 @@
 require_relative 'rubocop/cop/lint/duplicate_elsif_condition'
 require_relative 'rubocop/cop/lint/duplicate_hash_key'
 require_relative 'rubocop/cop/lint/duplicate_methods'
+require_relative 'rubocop/cop/lint/duplicate_require'
 require_relative 'rubocop/cop/lint/duplicate_rescue_exception'
 require_relative 'rubocop/cop/lint/each_with_object_argument'
 require_relative 'rubocop/cop/lint/else_layout'

lib/rubocop/cop/lint/duplicate_require.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for duplicate `require`s and `require_relative`s.
+      #
+      # @example
+      #   # bad
+      #   require 'foo'
+      #   require 'bar'
+      #   require 'foo'
+      #
+      #   # good
+      #   require 'foo'
+      #   require 'bar'
+      #
+      class DuplicateRequire < Base
+        MSG = 'Duplicate `%<method>s` detected.'
+        REQUIRE_METHODS = %i[require require_relative].freeze
+
+        def_node_matcher :require_call?, <<~PATTERN
+          (send {nil? (const _ :Kernel)} {:#{REQUIRE_METHODS.join(' :')}} _)
+        PATTERN
+
+        def on_new_investigation
+          # Holds the known required files for a given parent node (used as key)
+          @required = Hash.new { |h, k| h[k] = Set.new }.compare_by_identity
+          super
+        end
+
+        def on_send(node)
+          return unless REQUIRE_METHODS.include?(node.method_name) && require_call?(node)
+          return if @required[node.parent].add?(node.first_argument)
+
+          add_offense(node, message: format(MSG, method: node.method_name))
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/duplicate_require_spec.rb

@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::DuplicateRequire do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense when duplicate `require` is detected' do
+    expect_offense(<<~RUBY)
+      require 'foo'
+      require 'foo'
+      ^^^^^^^^^^^^^ Duplicate `require` detected.
+    RUBY
+  end
+
+  it 'registers an offense when duplicate `require_relative` is detected' do
+    expect_offense(<<~RUBY)
+      require_relative '../bar'
+      require_relative '../bar'
+      ^^^^^^^^^^^^^^^^^^^^^^^^^ Duplicate `require_relative` detected.
+    RUBY
+  end
+
+  it 'registers an offense when duplicate `require` through `Kernel` is detected' do
+    expect_offense(<<~RUBY)
+      require 'foo'
+      Kernel.require 'foo'
+      ^^^^^^^^^^^^^^^^^^^^ Duplicate `require` detected.
+    RUBY
+  end
+
+  it 'registers an offense for multiple duplicate requires' do
+    expect_offense(<<~RUBY)
+      require 'foo'
+      require_relative '../bar'
+      require 'foo/baz'
+      require_relative '../bar'
+      ^^^^^^^^^^^^^^^^^^^^^^^^^ Duplicate `require_relative` detected.
+      Kernel.require 'foo'
+      ^^^^^^^^^^^^^^^^^^^^ Duplicate `require` detected.
+      require 'quux'
+    RUBY
+  end
+
+  it 'registers an offense when duplicate requires are interleaved with some other code' do
+    expect_offense(<<~RUBY)
+      require 'foo'
+      def m
+      end
+      require 'foo'
+      ^^^^^^^^^^^^^ Duplicate `require` detected.
+    RUBY
+  end
+
+  it 'registers an offense for duplicate non top-level requires' do
+    expect_offense(<<~RUBY)
+      def m
+        require 'foo'
+        require 'foo'
+        ^^^^^^^^^^^^^ Duplicate `require` detected.
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when there are no duplicate `require`s' do
+    expect_no_offenses(<<~RUBY)
+      require 'foo'
+      require 'bar'
+    RUBY
+  end
+
+  it 'does not register an offense when using single `require`' do
+    expect_no_offenses(<<~RUBY)
+      require 'foo'
+    RUBY
+  end
+
+  it 'does not register an offense when calling user-defined `require` method' do
+    expect_no_offenses(<<~RUBY)
+      params.require(:user)
+      params.require(:user)
+    RUBY
+  end
+end