diff-lcs has changed its format in 1.4

.travis.yml

@@ -38,6 +38,8 @@ matrix:
   include:
     - rvm: jruby-1.7
       env: JRUBY_OPTS='--dev --1.8'
+    - rvm: 2.7.1
+      env: DIFF_LCS_VERSION="~> 1.3.0"
   allow_failures:
     - rvm: jruby-head
     - rvm: ruby-head

Gemfile

@@ -21,6 +21,12 @@ else
   gem 'rake', '>= 12.3.3'
 end
 
+if ENV['DIFF_LCS_VERSION']
+  gem 'diff-lcs', ENV['DIFF_LCS_VERSION']
+else
+  gem 'diff-lcs', '~> 1.4', '>= 1.4.3'
+end
+
 if RUBY_VERSION < '2.2.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/)
   gem "childprocess", "< 1.0.0"
 elsif RUBY_VERSION < '2.3.0'

lib/rspec/support/spec.rb

@@ -2,6 +2,7 @@
 require 'rspec/support/spec/in_sub_process'
 
 RSpec::Support.require_rspec_support "spec/deprecation_helpers"
+RSpec::Support.require_rspec_support "spec/diff_helpers"
 RSpec::Support.require_rspec_support "spec/with_isolated_stderr"
 RSpec::Support.require_rspec_support "spec/stderr_splitter"
 RSpec::Support.require_rspec_support "spec/formatting_support"

lib/rspec/support/spec/diff_helpers.rb

@@ -0,0 +1,29 @@
+require 'diff/lcs'
+
+module RSpec
+  module Support
+    module Spec
+      module DiffHelpers
+        # In the updated version of diff-lcs several diff headers change format slightly
+        # compensate for this and change minimum version in RSpec 4
+        if ::Diff::LCS::VERSION.to_f < 1.4
+          def one_line_header(line_number=2)
+            "-1,#{line_number} +1,#{line_number}"
+          end
+
+          def removing_two_line_header
+            "-1,3 +1"
+          end
+        else
+          def one_line_header(_=2)
+            "-1 +1"
+          end
+
+          def removing_two_line_header
+            "-1,3 +1,5"
+          end
+        end
+      end
+    end
+  end
+end