Rubocop 1.51.0 or later didn't support Ruby 2.6

bundler/spec/support/path.rb

@@ -292,11 +292,11 @@ def ruby_core_tarball?
     end
 
     def rubocop_gemfile_basename
-      tool_dir.join("rubocop_gems.rb")
+      tool_dir.join(RUBY_VERSION.start_with?("2.6") ? "rubocop26_gems.rb" : "rubocop_gems.rb")
     end
 
     def standard_gemfile_basename
-      tool_dir.join("standard_gems.rb")
+      tool_dir.join(RUBY_VERSION.start_with?("2.6") ? "standard26_gems.rb" : "standard_gems.rb")
     end
 
     def tool_dir

tool/bundler/rubocop26_gems.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "rubocop", "< 1.51.0"
+
+gem "minitest"
+gem "rake"
+gem "rake-compiler"
+gem "rspec"
+gem "test-unit"
+gem "rb_sys"

tool/bundler/rubocop26_gems.rb.lock

@@ -0,0 +1,64 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.2)
+    diff-lcs (1.5.0)
+    json (2.6.3)
+    minitest (5.18.0)
+    parallel (1.23.0)
+    parser (3.2.2.3)
+      ast (~> 2.4.1)
+      racc
+    power_assert (2.0.3)
+    racc (1.7.1)
+    rainbow (3.1.1)
+    rake (13.0.6)
+    rake-compiler (1.2.3)
+      rake
+    rb_sys (0.9.79)
+    regexp_parser (2.8.1)
+    rexml (3.2.5)
+    rspec (3.12.0)
+      rspec-core (~> 3.12.0)
+      rspec-expectations (~> 3.12.0)
+      rspec-mocks (~> 3.12.0)
+    rspec-core (3.12.2)
+      rspec-support (~> 3.12.0)
+    rspec-expectations (3.12.3)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-mocks (3.12.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-support (3.12.0)
+    rubocop (1.50.2)
+      json (~> 2.3)
+      parallel (~> 1.10)
+      parser (>= 3.2.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.28.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.29.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    test-unit (3.6.0)
+      power_assert
+    unicode-display_width (2.4.2)
+
+PLATFORMS
+  arm64-darwin-23
+
+DEPENDENCIES
+  minitest
+  rake
+  rake-compiler
+  rb_sys
+  rspec
+  rubocop (< 1.51.0)
+  test-unit
+
+BUNDLED WITH
+   2.4.13

tool/bundler/standard26_gems.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "standard", "~> 1.0"
+gem "rubocop", "< 1.51.0"
+
+gem "minitest"
+gem "rake"
+gem "rake-compiler"
+gem "rspec"
+gem "test-unit"
+gem "rb_sys"

tool/bundler/standard26_gems.rb.lock

@@ -0,0 +1,81 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.2)
+    diff-lcs (1.5.0)
+    json (2.6.3)
+    language_server-protocol (3.17.0.3)
+    lint_roller (1.0.0)
+    minitest (5.18.0)
+    parallel (1.23.0)
+    parser (3.2.2.3)
+      ast (~> 2.4.1)
+      racc
+    power_assert (2.0.3)
+    racc (1.7.1)
+    rainbow (3.1.1)
+    rake (13.0.6)
+    rake-compiler (1.2.3)
+      rake
+    rb_sys (0.9.79)
+    regexp_parser (2.8.1)
+    rexml (3.2.5)
+    rspec (3.12.0)
+      rspec-core (~> 3.12.0)
+      rspec-expectations (~> 3.12.0)
+      rspec-mocks (~> 3.12.0)
+    rspec-core (3.12.2)
+      rspec-support (~> 3.12.0)
+    rspec-expectations (3.12.3)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-mocks (3.12.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.12.0)
+    rspec-support (3.12.0)
+    rubocop (1.50.2)
+      json (~> 2.3)
+      parallel (~> 1.10)
+      parser (>= 3.2.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.28.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.29.0)
+      parser (>= 3.2.1.0)
+    rubocop-performance (1.16.0)
+      rubocop (>= 1.7.0, < 2.0)
+      rubocop-ast (>= 0.4.0)
+    ruby-progressbar (1.13.0)
+    standard (1.28.5)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.50.2)
+      standard-custom (~> 1.0.0)
+      standard-performance (~> 1.0.1)
+    standard-custom (1.0.1)
+      lint_roller (~> 1.0)
+    standard-performance (1.0.1)
+      lint_roller (~> 1.0)
+      rubocop-performance (~> 1.16.0)
+    test-unit (3.6.0)
+      power_assert
+    unicode-display_width (2.4.2)
+
+PLATFORMS
+  arm64-darwin-23
+
+DEPENDENCIES
+  minitest
+  rake
+  rake-compiler
+  rb_sys
+  rspec
+  rubocop (< 1.51.0)
+  standard (~> 1.0)
+  test-unit
+
+BUNDLED WITH
+   2.4.13