Remove usage of strip_heredoc in the framework in favor of <<~

Some places we can't remove because Ruby still don't have a method
equivalent to strip_heredoc to be called in an already existent string.

.rubocop.yml

 AllCops:
-  TargetRubyVersion: 2.2
+  TargetRubyVersion: 2.3
   # RuboCop has a bunch of cops enabled by default. This setting tells RuboCop
   # to ignore them, so only the ones explicitly set in this file are enabled.
   DisabledByDefault: true

actionpack/lib/action_controller/metal/request_forgery_protection.rb

@@ -3,7 +3,6 @@
 require "rack/session/abstract/id"
 require "action_controller/metal/exceptions"
 require "active_support/security_utils"
-require "active_support/core_ext/string/strip"
 
 module ActionController #:nodoc:
   class InvalidAuthenticityToken < ActionControllerError #:nodoc:
@@ -416,7 +415,7 @@ def protect_against_forgery? # :doc:
         allow_forgery_protection
       end
 
-      NULL_ORIGIN_MESSAGE = <<-MSG.strip_heredoc
+      NULL_ORIGIN_MESSAGE = <<~MSG
         The browser returned a 'null' origin for a request with origin-based forgery protection turned on. This usually
         means you have the 'no-referrer' Referrer-Policy header enabled, or that you the request came from a site that
         refused to give its origin. This makes it impossible for Rails to verify the source of the requests. Likely the

actionpack/lib/action_dispatch/routing/inspector.rb

 # frozen_string_literal: true
 
 require "delegate"
-require "active_support/core_ext/string/strip"
 
 module ActionDispatch
   module Routing
@@ -150,10 +149,10 @@ def header(routes)
       def no_routes(routes)
         @buffer <<
         if routes.none?
-          <<-MESSAGE.strip_heredoc
-          You don't have any routes defined!
+          <<~MESSAGE
+            You don't have any routes defined!
 
-          Please add some routes in config/routes.rb.
+            Please add some routes in config/routes.rb.
           MESSAGE
         else
           "No routes were found for this controller"
@@ -203,7 +202,7 @@ def header(routes)
       end
 
       def no_routes(*)
-        @buffer << <<-MESSAGE.strip_heredoc
+        @buffer << <<~MESSAGE
           <p>You don't have any routes defined!</p>
           <ul>
             <li>Please add some routes in <tt>config/routes.rb</tt>.</li>

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -611,7 +611,7 @@ def mount(app, options = nil)
           end
 
           raise ArgumentError, "A rack application must be specified" unless app.respond_to?(:call)
-          raise ArgumentError, <<-MSG.strip_heredoc unless path
+          raise ArgumentError, <<~MSG unless path
             Must be called with mount point
 
               mount SomeRackApp, at: "some_route"

actionpack/test/controller/parameters/serialization_test.rb

@@ -2,7 +2,6 @@
 
 require "abstract_unit"
 require "action_controller/metal/strong_parameters"
-require "active_support/core_ext/string/strip"
 
 class ParametersSerializationTest < ActiveSupport::TestCase
   setup do
@@ -31,7 +30,7 @@ class ParametersSerializationTest < ActiveSupport::TestCase
   end
 
   test "yaml backwardscompatible with psych 2.0.8 format" do
-    params = YAML.load <<-end_of_yaml.strip_heredoc
+    params = YAML.load <<~end_of_yaml
       --- !ruby/hash:ActionController::Parameters
       key: :value
     end_of_yaml
@@ -41,7 +40,7 @@ class ParametersSerializationTest < ActiveSupport::TestCase
   end
 
   test "yaml backwardscompatible with psych 2.0.9+ format" do
-    params = YAML.load(<<-end_of_yaml.strip_heredoc)
+    params = YAML.load(<<~end_of_yaml)
       --- !ruby/hash-with-ivars:ActionController::Parameters
       elements:
         key: :value

activemodel/test/cases/errors_test.rb

 # frozen_string_literal: true
 
 require "cases/helper"
-require "active_support/core_ext/string/strip"
 require "yaml"
 
 class ErrorsTest < ActiveModel::TestCase
@@ -406,7 +405,7 @@ def test_no_key
   end
 
   test "errors are backward compatible with the Rails 4.2 format" do
-    yaml = <<-CODE.strip_heredoc
+    yaml = <<~CODE
     --- !ruby/object:ActiveModel::Errors
     base: &1 !ruby/object:ErrorsTest::Person
       errors: !ruby/object:ActiveModel::Errors

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -131,7 +131,7 @@ def primary_key=(value)
             def suppress_composite_primary_key(pk)
               return pk unless pk.is_a?(Array)
 
-              warn <<-WARNING.strip_heredoc
+              warn <<~WARNING
                 WARNING: Active Record does not support composite primary key.
 
                 #{table_name} has composite primary key. Composite primary key is ignored.

activerecord/lib/active_record/attribute_methods/serialization.rb

@@ -7,7 +7,7 @@ module Serialization
 
       class ColumnNotSerializableError < StandardError
         def initialize(name, type)
-          super <<-EOS.strip_heredoc
+          super <<~EOS
             Column `#{name}` of type #{type.class} does not support `serialize` feature.
             Usually it means that you are trying to use `serialize`
             on a column that already implements serialization natively.

activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb

 # frozen_string_literal: true
 
-require "active_support/core_ext/string/strip"
-
 module ActiveRecord
   module ConnectionAdapters
     class AbstractAdapter
@@ -66,7 +64,7 @@ def visit_PrimaryKeyDefinition(o)
           end
 
           def visit_ForeignKeyDefinition(o)
-            sql = <<-SQL.strip_heredoc
+            sql = <<~SQL
               CONSTRAINT #{quote_column_name(o.name)}
               FOREIGN KEY (#{quote_column_name(o.column)})
                 REFERENCES #{quote_table_name(o.to_table)} (#{quote_column_name(o.primary_key)})
@@ -133,7 +131,7 @@ def action_sql(action, dependency)
             when :cascade  then "ON #{action} CASCADE"
             when :restrict then "ON #{action} RESTRICT"
             else
-              raise ArgumentError, <<-MSG.strip_heredoc
+              raise ArgumentError, <<~MSG
                 '#{dependency}' is not supported for :on_update or :on_delete.
                 Supported values are: :nullify, :cascade, :restrict
               MSG

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -11,8 +11,6 @@
 require "active_record/connection_adapters/mysql/schema_statements"
 require "active_record/connection_adapters/mysql/type_metadata"
 
-require "active_support/core_ext/string/strip"
-
 module ActiveRecord
   module ConnectionAdapters
     class AbstractMysqlAdapter < AbstractAdapter
@@ -284,7 +282,7 @@ def truncate(table_name, name = nil)
       def table_comment(table_name) # :nodoc:
         scope = quoted_scope(table_name)
 
-        query_value(<<-SQL.strip_heredoc, "SCHEMA").presence
+        query_value(<<~SQL, "SCHEMA").presence
           SELECT table_comment
           FROM information_schema.tables
           WHERE table_schema = #{scope[:schema]}
@@ -392,7 +390,7 @@ def foreign_keys(table_name)
 
         scope = quoted_scope(table_name)
 
-        fk_info = exec_query(<<-SQL.strip_heredoc, "SCHEMA")
+        fk_info = exec_query(<<~SQL, "SCHEMA")
           SELECT fk.referenced_table_name AS 'to_table',
                  fk.referenced_column_name AS 'primary_key',
                  fk.column_name AS 'column',
@@ -480,7 +478,7 @@ def primary_keys(table_name) # :nodoc:
 
         scope = quoted_scope(table_name)
 
-        query_values(<<-SQL.strip_heredoc, "SCHEMA")
+        query_values(<<~SQL, "SCHEMA")
           SELECT column_name
           FROM information_schema.key_column_usage
           WHERE constraint_name = 'PRIMARY'

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -115,7 +115,7 @@ def indexes(table_name) # :nodoc:
             if indkey.include?(0)
               columns = expressions
             else
-              columns = Hash[query(<<-SQL.strip_heredoc, "SCHEMA")].values_at(*indkey).compact
+              columns = Hash[query(<<~SQL, "SCHEMA")].values_at(*indkey).compact
                 SELECT a.attnum, a.attname
                 FROM pg_attribute a
                 WHERE a.attrelid = #{oid}
@@ -158,7 +158,7 @@ def table_options(table_name) # :nodoc:
         def table_comment(table_name) # :nodoc:
           scope = quoted_scope(table_name, type: "BASE TABLE")
           if scope[:name]
-            query_value(<<-SQL.strip_heredoc, "SCHEMA")
+            query_value(<<~SQL, "SCHEMA")
               SELECT pg_catalog.obj_description(c.oid, 'pg_class')
               FROM pg_catalog.pg_class c
                 LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
@@ -353,7 +353,7 @@ def pk_and_sequence_for(table) #:nodoc:
         end
 
         def primary_keys(table_name) # :nodoc:
-          query_values(<<-SQL.strip_heredoc, "SCHEMA")
+          query_values(<<~SQL, "SCHEMA")
             SELECT a.attname
               FROM (
                      SELECT indrelid, indkey, generate_subscripts(indkey, 1) idx
@@ -502,7 +502,7 @@ def rename_index(table_name, old_name, new_name)
 
         def foreign_keys(table_name)
           scope = quoted_scope(table_name)
-          fk_info = exec_query(<<-SQL.strip_heredoc, "SCHEMA")
+          fk_info = exec_query(<<~SQL, "SCHEMA")
             SELECT t2.oid::regclass::text AS to_table, a1.attname AS column, a2.attname AS primary_key, c.conname AS name, c.confupdtype AS on_update, c.confdeltype AS on_delete, c.convalidated AS valid
             FROM pg_constraint c
             JOIN pg_class t1 ON c.conrelid = t1.oid

activerecord/lib/active_record/errors.rb

@@ -120,13 +120,13 @@ class MismatchedForeignKey < StatementInvalid
     def initialize(adapter = nil, message: nil, table: nil, foreign_key: nil, target_table: nil, primary_key: nil)
       @adapter = adapter
       if table
-        msg = <<-EOM.strip_heredoc
+        msg = <<~EOM
           Column `#{foreign_key}` on table `#{table}` has a type of `#{column_type(table, foreign_key)}`.
           This does not match column `#{primary_key}` on `#{target_table}`, which has type `#{column_type(target_table, primary_key)}`.
           To resolve this issue, change the type of the `#{foreign_key}` column on `#{table}` to be :integer. (For example `t.integer #{foreign_key}`).
         EOM
       else
-        msg = <<-EOM
+        msg = <<~EOM
           There is a mismatch between the foreign key and primary key column types.
           Verify that the foreign key column type and the primary key of the associated table match types.
         EOM

activerecord/lib/active_record/migration/command_recorder.rb

@@ -85,7 +85,7 @@ def record(*command, &block)
       # invert the +command+.
       def inverse_of(command, args, &block)
         method = :"invert_#{command}"
-        raise IrreversibleMigration, <<-MSG.strip_heredoc unless respond_to?(method, true)
+        raise IrreversibleMigration, <<~MSG unless respond_to?(method, true)
           This migration uses #{command}, which is not automatically reversible.
           To make the migration reversible you can either:
           1. Define #up and #down methods in place of the #change method.

activerecord/test/cases/core_test.rb

@@ -4,7 +4,6 @@
 require "models/person"
 require "models/topic"
 require "pp"
-require "active_support/core_ext/string/strip"
 
 class NonExistentTable < ActiveRecord::Base; end
 
@@ -39,26 +38,26 @@ def test_pretty_print_new
     topic = Topic.new
     actual = "".dup
     PP.pp(topic, StringIO.new(actual))
-    expected = <<-PRETTY.strip_heredoc
-    #<Topic:0xXXXXXX
-     id: nil,
-     title: nil,
-     author_name: nil,
-     author_email_address: "test@test.com",
-     written_on: nil,
-     bonus_time: nil,
-     last_read: nil,
-     content: nil,
-     important: nil,
-     approved: true,
-     replies_count: 0,
-     unique_replies_count: 0,
-     parent_id: nil,
-     parent_title: nil,
-     type: nil,
-     group: nil,
-     created_at: nil,
-     updated_at: nil>
+    expected = <<~PRETTY
+      #<Topic:0xXXXXXX
+       id: nil,
+       title: nil,
+       author_name: nil,
+       author_email_address: "test@test.com",
+       written_on: nil,
+       bonus_time: nil,
+       last_read: nil,
+       content: nil,
+       important: nil,
+       approved: true,
+       replies_count: 0,
+       unique_replies_count: 0,
+       parent_id: nil,
+       parent_title: nil,
+       type: nil,
+       group: nil,
+       created_at: nil,
+       updated_at: nil>
     PRETTY
     assert actual.start_with?(expected.split("XXXXXX").first)
     assert actual.end_with?(expected.split("XXXXXX").last)
@@ -68,26 +67,26 @@ def test_pretty_print_persisted
     topic = topics(:first)
     actual = "".dup
     PP.pp(topic, StringIO.new(actual))
-    expected = <<-PRETTY.strip_heredoc
-    #<Topic:0x\\w+
-     id: 1,
-     title: "The First Topic",
-     author_name: "David",
-     author_email_address: "david@loudthinking.com",
-     written_on: 2003-07-16 14:28:11 UTC,
-     bonus_time: 2000-01-01 14:28:00 UTC,
-     last_read: Thu, 15 Apr 2004,
-     content: "Have a nice day",
-     important: nil,
-     approved: false,
-     replies_count: 1,
-     unique_replies_count: 0,
-     parent_id: nil,
-     parent_title: nil,
-     type: nil,
-     group: nil,
-     created_at: [^,]+,
-     updated_at: [^,>]+>
+    expected = <<~PRETTY
+      #<Topic:0x\\w+
+       id: 1,
+       title: "The First Topic",
+       author_name: "David",
+       author_email_address: "david@loudthinking.com",
+       written_on: 2003-07-16 14:28:11 UTC,
+       bonus_time: 2000-01-01 14:28:00 UTC,
+       last_read: Thu, 15 Apr 2004,
+       content: "Have a nice day",
+       important: nil,
+       approved: false,
+       replies_count: 1,
+       unique_replies_count: 0,
+       parent_id: nil,
+       parent_title: nil,
+       type: nil,
+       group: nil,
+       created_at: [^,]+,
+       updated_at: [^,>]+>
     PRETTY
     assert_match(/\A#{expected}\z/, actual)
   end

activerecord/test/cases/explain_test.rb

@@ -2,7 +2,6 @@
 
 require "cases/helper"
 require "models/car"
-require "active_support/core_ext/string/strip"
 
 if ActiveRecord::Base.connection.supports_explain?
   class ExplainTest < ActiveRecord::TestCase
@@ -53,7 +52,7 @@ def test_exec_explain_with_binds
       queries = sqls.zip(binds)
 
       stub_explain_for_query_plans(["query plan foo\n", "query plan bar\n"]) do
-        expected = <<-SQL.strip_heredoc
+        expected = <<~SQL
           EXPLAIN for: #{sqls[0]} [["wadus", 1]]
           query plan foo
 

activerecord/test/cases/fixtures_test.rb

@@ -86,7 +86,7 @@ def test_bulk_insert_multiple_table_with_a_multi_statement_query
 
       create_fixtures("bulbs", "authors", "computers")
 
-      expected_sql = <<-EOS.strip_heredoc.chop
+      expected_sql = <<~EOS
         INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("bulbs")} .*
         INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("authors")} .*
         INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("computers")} .*

activerecord/test/cases/migration/rename_table_test.rb

@@ -88,7 +88,7 @@ def test_renaming_table_renames_primary_key
           assert connection.table_exists? :felines
           assert_not connection.table_exists? :cats
 
-          primary_key_name = connection.select_values(<<-SQL.strip_heredoc, "SCHEMA")[0]
+          primary_key_name = connection.select_values(<<~SQL, "SCHEMA")[0]
             SELECT c.relname
               FROM pg_class c
               JOIN pg_index i

activesupport/lib/active_support/testing/time_helpers.rb

 # frozen_string_literal: true
 
 require "active_support/core_ext/module/redefine_method"
-require "active_support/core_ext/string/strip" # for strip_heredoc
 require "active_support/core_ext/time/calculations"
 require "concurrent/map"
 
@@ -112,7 +111,7 @@ def travel(duration, &block)
       #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
       def travel_to(date_or_time)
         if block_given? && simple_stubs.stubbing(Time, :now)
-          travel_to_nested_block_call = <<-MSG.strip_heredoc
+          travel_to_nested_block_call = <<~MSG
 
       Calling `travel_to` with a block, when we have previously already made a call to `travel_to`, can lead to confusing time stubbing.
 

activesupport/test/core_ext/string_ext_test.rb

@@ -9,9 +9,9 @@
 require "active_support/inflector"
 require "active_support/core_ext/string"
 require "active_support/time"
-require "active_support/core_ext/string/strip"
 require "active_support/core_ext/string/output_safety"
 require "active_support/core_ext/string/indent"
+require "active_support/core_ext/string/strip"
 require "time_zone_test_helpers"
 require "yaml"
 

activesupport/test/core_ext/time_with_zone_test.rb

@@ -3,7 +3,6 @@
 require "abstract_unit"
 require "active_support/time"
 require "time_zone_test_helpers"
-require "active_support/core_ext/string/strip"
 require "yaml"
 
 class TimeWithZoneTest < ActiveSupport::TestCase
@@ -163,7 +162,7 @@ def test_rfc3339_with_fractional_seconds
   end
 
   def test_to_yaml
-    yaml = <<-EOF.strip_heredoc
+    yaml = <<~EOF
       --- !ruby/object:ActiveSupport::TimeWithZone
       utc: 2000-01-01 00:00:00.000000000 Z
       zone: !ruby/object:ActiveSupport::TimeZone
@@ -175,7 +174,7 @@ def test_to_yaml
   end
 
   def test_ruby_to_yaml
-    yaml = <<-EOF.strip_heredoc
+    yaml = <<~EOF
       ---
       twz: !ruby/object:ActiveSupport::TimeWithZone
         utc: 2000-01-01 00:00:00.000000000 Z
@@ -188,7 +187,7 @@ def test_ruby_to_yaml
   end
 
   def test_yaml_load
-    yaml = <<-EOF.strip_heredoc
+    yaml = <<~EOF
       --- !ruby/object:ActiveSupport::TimeWithZone
       utc: 2000-01-01 00:00:00.000000000 Z
       zone: !ruby/object:ActiveSupport::TimeZone
@@ -200,7 +199,7 @@ def test_yaml_load
   end
 
   def test_ruby_yaml_load
-    yaml = <<-EOF.strip_heredoc
+    yaml = <<~EOF
       ---
       twz: !ruby/object:ActiveSupport::TimeWithZone
         utc: 2000-01-01 00:00:00.000000000 Z

railties/lib/rails/generators/actions.rb

 # frozen_string_literal: true
 
+require "active_support/core_ext/string/strip"
+
 module Rails
   module Generators
     module Actions

railties/lib/rails/generators/app_base.rb

@@ -2,7 +2,6 @@
 
 require "fileutils"
 require "digest/md5"
-require "active_support/core_ext/string/strip"
 require "rails/version" unless defined?(Rails::VERSION)
 require "open-uri"
 require "uri"

railties/lib/rails/generators/rails/credentials/credentials_generator.rb

@@ -2,7 +2,6 @@
 
 require "rails/generators/base"
 require "rails/generators/rails/master_key/master_key_generator"
-require "active_support/core_ext/string/strip"
 require "active_support/encrypted_configuration"
 
 module Rails
@@ -43,13 +42,13 @@ def credentials
         end
 
         def credentials_template
-          <<-YAML.strip_heredoc
-          # aws:
-          #   access_key_id: 123
-          #   secret_access_key: 345
+          <<~YAML
+            # aws:
+            #   access_key_id: 123
+            #   secret_access_key: 345
 
-          # Used as the base secret for all MessageVerifiers in Rails, including the one protecting cookies.
-          secret_key_base: #{SecureRandom.hex(64)}
+            # Used as the base secret for all MessageVerifiers in Rails, including the one protecting cookies.
+            secret_key_base: #{SecureRandom.hex(64)}
           YAML
         end
     end

railties/lib/rails/generators/rails/encrypted_file/encrypted_file_generator.rb

@@ -16,10 +16,10 @@ def add_encrypted_file_silently(file_path, key_path, template = encrypted_file_t
 
       private
         def encrypted_file_template
-          <<-YAML.strip_heredoc
-          # aws:
-          #   access_key_id: 123
-          #   secret_access_key: 345
+          <<~YAML
+            # aws:
+            #   access_key_id: 123
+            #   secret_access_key: 345
 
           YAML
         end

railties/lib/rails/generators/rails/plugin/templates/app/controllers/%namespaced_name%/application_controller.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class ApplicationController < ActionController::#{api? ? "API" : "Base"}
     #{ api? ? '# ' : '' }protect_from_forgery with: :exception
   end

railties/lib/rails/generators/rails/plugin/templates/app/helpers/%namespaced_name%/application_helper.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   module ApplicationHelper
   end
 rb

railties/lib/rails/generators/rails/plugin/templates/app/jobs/%namespaced_name%/application_job.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class ApplicationJob < ActiveJob::Base
   end
 rb

railties/lib/rails/generators/rails/plugin/templates/app/mailers/%namespaced_name%/application_mailer.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class ApplicationMailer < ActionMailer::Base
     default from: 'from@example.com'
     layout 'mailer'

railties/lib/rails/generators/rails/plugin/templates/app/models/%namespaced_name%/application_record.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class ApplicationRecord < ActiveRecord::Base
     self.abstract_class = true
   end

railties/lib/rails/generators/rails/plugin/templates/lib/%namespaced_name%/engine.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class Engine < ::Rails::Engine
   #{mountable? ? '  isolate_namespace ' + camelized_modules : ' '}
   #{api? ? "  config.generators.api_only = true" : ' '}

railties/lib/rails/generators/rails/plugin/templates/lib/%namespaced_name%/railtie.rb.tt

-<%= wrap_in_modules <<-rb.strip_heredoc
+<%= wrap_in_modules <<~rb
   class Railtie < ::Rails::Railtie
   end
 rb

railties/lib/rails/secrets.rb

@@ -2,7 +2,6 @@
 
 require "yaml"
 require "active_support/message_encryptor"
-require "active_support/core_ext/string/strip"
 
 module Rails
   # Greatly inspired by Ara T. Howard's magnificent sekrets gem. 😘

railties/test/application/rake_test.rb

@@ -2,7 +2,6 @@
 
 require "isolation/abstract_unit"
 require "env_helpers"
-require "active_support/core_ext/string/strip"
 
 module ApplicationTests
   class RakeTest < ActiveSupport::TestCase
@@ -131,7 +130,7 @@ def test_rails_routes_calls_the_route_inspector
       RUBY
 
       output = rails("routes")
-      assert_equal <<-MESSAGE.strip_heredoc, output
+      assert_equal <<~MESSAGE, output
                               Prefix Verb URI Pattern                                                                       Controller#Action
                                 cart GET  /cart(.:format)                                                                   cart#show
                   rails_service_blob GET  /rails/active_storage/blobs/:signed_id/*filename(.:format)                        active_storage/blobs#show
@@ -173,7 +172,7 @@ def test_rails_routes_with_global_search_key
       RUBY
 
       output = rails("routes", "-g", "show")
-      assert_equal <<-MESSAGE.strip_heredoc, output
+      assert_equal <<~MESSAGE, output
                               Prefix Verb URI Pattern                                                                       Controller#Action
                                 cart GET  /cart(.:format)                                                                   cart#show
                   rails_service_blob GET  /rails/active_storage/blobs/:signed_id/*filename(.:format)                        active_storage/blobs#show
@@ -183,7 +182,7 @@ def test_rails_routes_with_global_search_key
       MESSAGE
 
       output = rails("routes", "-g", "POST")
-      assert_equal <<-MESSAGE.strip_heredoc, output
+      assert_equal <<~MESSAGE, output
                               Prefix Verb URI Pattern                                    Controller#Action
                                      POST /cart(.:format)                                cart#create
                 rails_direct_uploads POST /rails/active_storage/direct_uploads(.:format) active_storage/direct_uploads#create
@@ -242,7 +241,7 @@ def test_rails_routes_displays_message_when_no_routes_are_defined
         end
       RUBY
 
-      assert_equal <<-MESSAGE.strip_heredoc, rails("routes")
+      assert_equal <<~MESSAGE, rails("routes")
                               Prefix Verb URI Pattern                                                                       Controller#Action
                   rails_service_blob GET  /rails/active_storage/blobs/:signed_id/*filename(.:format)                        active_storage/blobs#show
                 rails_blob_variation GET  /rails/active_storage/variants/:signed_blob_id/:variation_key/*filename(.:format) active_storage/variants#show
@@ -262,7 +261,7 @@ def test_rake_routes_with_rake_options
 
       output = Dir.chdir(app_path) { `bin/rake --rakefile Rakefile routes` }
 
-      assert_equal <<-MESSAGE.strip_heredoc, output
+      assert_equal <<~MESSAGE, output
                               Prefix Verb URI Pattern                                                                       Controller#Action
                                 cart GET  /cart(.:format)                                                                   cart#show
                   rails_service_blob GET  /rails/active_storage/blobs/:signed_id/*filename(.:format)                        active_storage/blobs#show

railties/test/application/test_runner_test.rb

 # frozen_string_literal: true
 
 require "isolation/abstract_unit"
-require "active_support/core_ext/string/strip"
 require "env_helpers"
 
 module ApplicationTests
@@ -741,7 +740,7 @@ def run_test_command(arguments = "test/unit/test_test.rb", **opts)
       def create_model_with_fixture
         rails "generate", "model", "user", "name:string"
 
-        app_file "test/fixtures/users.yml", <<-YAML.strip_heredoc
+        app_file "test/fixtures/users.yml", <<~YAML
           vampire:
             id: 1
             name: Koyomi Araragi

railties/test/generators/model_generator_test.rb

@@ -2,7 +2,6 @@
 
 require "generators/generators_test_helper"
 require "rails/generators/rails/model/model_generator"
-require "active_support/core_ext/string/strip"
 
 class ModelGeneratorTest < Rails::Generators::TestCase
   include GeneratorsTestHelper
@@ -379,10 +378,10 @@ def test_add_uuid_to_create_table_migration
   def test_required_belongs_to_adds_required_association
     run_generator ["account", "supplier:references{required}"]
 
-    expected_file = <<-FILE.strip_heredoc
-    class Account < ApplicationRecord
-      belongs_to :supplier, required: true
-    end
+    expected_file = <<~FILE
+      class Account < ApplicationRecord
+        belongs_to :supplier, required: true
+      end
     FILE
     assert_file "app/models/account.rb", expected_file
   end
@@ -390,10 +389,10 @@ class Account < ApplicationRecord
   def test_required_polymorphic_belongs_to_generages_correct_model
     run_generator ["account", "supplier:references{required,polymorphic}"]
 
-    expected_file = <<-FILE.strip_heredoc
-    class Account < ApplicationRecord
-      belongs_to :supplier, polymorphic: true, required: true
-    end
+    expected_file = <<~FILE
+      class Account < ApplicationRecord
+        belongs_to :supplier, polymorphic: true, required: true
+      end
     FILE
     assert_file "app/models/account.rb", expected_file
   end
@@ -401,10 +400,10 @@ class Account < ApplicationRecord
   def test_required_and_polymorphic_are_order_independent
     run_generator ["account", "supplier:references{polymorphic.required}"]
 
-    expected_file = <<-FILE.strip_heredoc
-    class Account < ApplicationRecord
-      belongs_to :supplier, polymorphic: true, required: true
-    end
+    expected_file = <<~FILE
+      class Account < ApplicationRecord
+        belongs_to :supplier, polymorphic: true, required: true
+      end
     FILE
     assert_file "app/models/account.rb", expected_file
   end
@@ -452,11 +451,11 @@ def test_foreign_key_is_skipped_for_polymorphic_references
 
   def test_token_option_adds_has_secure_token
     run_generator ["user", "token:token", "auth_token:token"]
-    expected_file = <<-FILE.strip_heredoc
-    class User < ApplicationRecord
-      has_secure_token
-      has_secure_token :auth_token
-    end
+    expected_file = <<~FILE
+      class User < ApplicationRecord
+        has_secure_token
+        has_secure_token :auth_token
+      end
     FILE
     assert_file "app/models/user.rb", expected_file
   end