1 files changed, 58 insertions, 0 deletions
diff --git a/test/prism/locals_test.rb b/test/prism/locals_test.rb
new file mode 100644
index 0000000000..0eb73f1b9c
--- /dev/null
+++ b/test/prism/locals_test.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+# This test is going to use the RubyVM::InstructionSequence class to compile
+# local tables and compare against them to ensure we have the same locals in the
+# same order. This is important to guarantee that we compile indices correctly
+# on CRuby (in terms of compatibility).
+#
+# There have also been changes made in other versions of Ruby, so we only want
+# to test on the most recent versions.
+return if !defined?(RubyVM::InstructionSequence) || RUBY_VERSION < "3.4.0"
+
+# Omit tests if running on a 32-bit machine because there is a bug with how
+# Ruby is handling large ISeqs on 32-bit machines
+return if RUBY_PLATFORM =~ /i686/
+
+require_relative "test_helper"
+
+module Prism
+  class LocalsTest < TestCase
+    base = File.join(__dir__, "fixtures")
+    Dir["**/*.txt", base: base].each do |relative|
+      # Skip this fixture because it has a different number of locals because
+      # CRuby is eliminating dead code.
+      next if relative == "whitequark/ruby_bug_10653.txt"
+
+      filepath = File.join(base, relative)
+      define_method("test_#{relative}") { assert_locals(filepath) }
+    end
+
+    def setup
+      @previous_default_external = Encoding.default_external
+      ignore_warnings { Encoding.default_external = Encoding::UTF_8 }
+    end
+
+    def teardown
+      ignore_warnings { Encoding.default_external = @previous_default_external }
+    end
+
+    private
+
+    def assert_locals(filepath)
+      source = File.read(filepath)
+
+      expected = Debug.cruby_locals(source)
+      actual = Debug.prism_locals(source)
+
+      assert_equal(expected, actual)
+    end
+
+    def ignore_warnings
+      previous_verbosity = $VERBOSE
+      $VERBOSE = nil
+      yield
+    ensure
+      $VERBOSE = previous_verbosity
+    end
+  end
+end